ViewDragHelper根据拖拽状态改变子view的背景

这几天的项目开发中，遇到了一个需求：在页面上显示一个悬浮按钮，并且可以在屏幕内拖动，根据悬浮按钮的状态不一样，悬浮按钮的背景也不一样。需求看起来很简单，我选择ViewDragHelper这个辅助类来实现这个功能。有目标，有想法，那我们开始实现吧。

说动手咱就动手，实现拖拽和改变拖动按钮最终的背景很简单，具体实现如下：

public class DragView extends FrameLayout {

private ViewDragHelper mDragger;
private ViewDragHelper.Callback callback;
private View dragView;
private boolean isVerticalMove;
private Point mAutoBackOriginPos = new Point();
private boolean isLeft;

public DragView(Context context) {
this(context, null);
}

public DragView(Context context, AttributeSet attrs) {
super(context, attrs);
callback = new DraggerCallBack();
//第二个参数就是滑动灵敏度的意思 可以随意设置
mDragger = ViewDragHelper.create(this, 1.0f, callback);
}

@Override
protected void onFinishInflate() {
super.onFinishInflate();
dragView = findViewById(R.id.tv_cash_back);
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
//决定是否拦截当前事件
return mDragger.shouldInterceptTouchEvent(ev);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
//处理事件
mDragger.processTouchEvent(event);
return true;
}

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
mAutoBackOriginPos.x = dragView.getLeft();
mAutoBackOriginPos.y = dragView.getTop();

}

/**
* 滚动
*/
@Override
public void computeScroll() {
if (mDragger.continueSettling(true)) {
invalidate();
}
}

class DraggerCallBack extends ViewDragHelper.Callback {

//这个地方实际上函数返回值为true就代表可以滑动 为false 则不能滑动
@Override
public boolean tryCaptureView(View child, int pointerId) {
Lg.d("tryCaptureView");
return true;
}

//这个地方实际上left就代表 你将要移动到的位置的坐标。返回值就是最终确定的移动的位置。
// 我们要让view滑动的范围在我们的layout之内
//实际上就是判断如果这个坐标在layout之内 那我们就返回这个坐标值。
//如果这个坐标在layout的边界处 那我们就只能返回边界的坐标给他。不能让他超出这个范围
//除此之外就是如果你的layout设置了padding的话，也可以让子view的活动范围在padding之内的.
@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {
Lg.d("clampViewPositionHorizontal");
//取得左边界的坐标
final int leftBound = getPaddingLeft();
//取得右边界的坐标
final int rightBound = getWidth() - child.getWidth() - leftBound;
//这个地方的含义就是 如果left的值 在leftbound和rightBound之间 那么就返回left
//如果left的值 比 leftbound还要小 那么就说明 超过了左边界 那我们只能返回给他左边界的值
//如果left的值 比rightbound还要大 那么就说明 超过了右边界，那我们只能返回给他右边界的值
return Math.min(Math.max(left, leftBound), rightBound);
}

//纵向的注释就不写了 自己体会
@Override
public int clampViewPositionVertical(View child, int top, int dy) {
Lg.d("clampViewPositionVertical");
final int topBound = getPaddingTop();
final int bottomBound = getHeight() - child.getHeight() - topBound;
return Math.min(Math.max(top, topBound), bottomBound);
}

//需要子view的点击事件时添加，并且在xml文件中设置click属性为true
@Override
public int getViewHorizontalDragRange(View child) {
Lg.d("getViewHorizontalDragRange");
if (ViewDragHelper.STATE_DRAGGING == mDragger.getViewDragState()) {
dragView.setBackgroundResource(R.drawable.icon_cash_back_draging);
}
return getMeasuredWidth() - child.getMeasuredWidth();
}

//需要子view的点击事件时添加，并且在xml文件中设置click属性为true
@Override
public int getViewVerticalDragRange(View child) {
Lg.d("getViewVerticalDragRange");
return getMeasuredHeight() - child.getMeasuredHeight();
}

@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
Lg.d("onViewReleased");
//手指释放时可以自动回去，实现回弹需要配合computeScroll方法的配合才能生效
//如果移动的位置大于屏幕的一半，那么就回到右侧，否则移动到左侧
if (releasedChild == dragView) {
isLeft = dragView.getLeft() + dragView.getWidth() / 2 - getMeasuredWidth() / 2 < 0;
mDragger.settleCapturedViewAt(isLeft ? 0 : mAutoBackOriginPos.x, isVerticalMove ? dragView.getTop()
: mAutoBackOriginPos.y);
dragView.setBackgroundResource(isLeft ? R.drawable.icon_cash_back_left : R.drawable.icon_cash_back);
invalidate();
}
}
}

}

在onViewReleased接口里面实现拖拽之后的背景更换，为什么选择这个接口？顾名思义，这个接口是在view拖动释放之后调用的接口，并且，还回去刷新UI，不在这里更换背景，在哪里更换呢？

接下来，我们需要实现的另外一个细节，当view拖动的时候，view的背景应该是另一个样子，不是view释放之后的任何一种背景，那么这个怎么去实现呢？

首先我们会想到的是在触摸事件中处理，当MotionEvent为move的时候，就去改变ui，貌似可以，感觉试试吧。

@Override
public boolean onTouchEvent(MotionEvent event) {
if(MotionEvent.ACTION_MOVE==event.getAction()){
dragView.setBackgroundResource(R.drawable.icon_cash_back_draging);
}
//处理事件
mDragger.processTouchEvent(event);
return true;
}

结果：view在屏幕上乱飞。第一猜想破产。

/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0 *
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package android.support.v4.widget;

import android.content.Context;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.VelocityTrackerCompat;
import android.support.v4.view.ViewCompat;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.animation.Interpolator;

import java.util.Arrays;

/**
* ViewDragHelper is a utility class for writing custom ViewGroups. It offers a number
* of useful operations and state tracking for allowing a user to drag and reposition
* views within their parent ViewGroup.
*/
public class ViewDragHelper {
private static final String TAG = "ViewDragHelper";

/**
* A null/invalid pointer ID.
*/
public static final int INVALID_POINTER = -1;

/**
* A view is not currently being dragged or animating as a result of a fling/snap.
*/
public static final int STATE_IDLE = 0;

/**
* A view is currently being dragged. The position is currently changing as a result
* of user input or simulated user input.
*/
public static final int STATE_DRAGGING = 1;

/**
* A view is currently settling into place as a result of a fling or
* predefined non-interactive motion.
*/
public static final int STATE_SETTLING = 2;

/**
* Edge flag indicating that the left edge should be affected.
*/
public static final int EDGE_LEFT = 1 << 0;

/**
* Edge flag indicating that the right edge should be affected.
*/
public static final int EDGE_RIGHT = 1 << 1;

/**
* Edge flag indicating that the top edge should be affected.
*/
public static final int EDGE_TOP = 1 << 2;

/**
* Edge flag indicating that the bottom edge should be affected.
*/
public static final int EDGE_BOTTOM = 1 << 3;

/**
* Edge flag set indicating all edges should be affected.
*/
public static final int EDGE_ALL = EDGE_LEFT | EDGE_TOP | EDGE_RIGHT | EDGE_BOTTOM;

/**
* Indicates that a check should occur along the horizontal axis
*/
public static final int DIRECTION_HORIZONTAL = 1 << 0;

/**
* Indicates that a check should occur along the vertical axis
*/
public static final int DIRECTION_VERTICAL = 1 << 1;

/**
* Indicates that a check should occur along all axes
*/
public static final int DIRECTION_ALL = DIRECTION_HORIZONTAL | DIRECTION_VERTICAL;

private static final int EDGE_SIZE = 20; // dp

private static final int BASE_SETTLE_DURATION = 256; // ms
private static final int MAX_SETTLE_DURATION = 600; // ms

// Current drag state; idle, dragging or settling
private int mDragState;

// Distance to travel before a drag may begin
private int mTouchSlop;

// Last known position/pointer tracking
private int mActivePointerId = INVALID_POINTER;
private float[] mInitialMotionX;
private float[] mInitialMotionY;
private float[] mLastMotionX;
private float[] mLastMotionY;
private int[] mInitialEdgesTouched;
private int[] mEdgeDragsInProgress;
private int[] mEdgeDragsLocked;
private int mPointersDown;

private VelocityTracker mVelocityTracker;
private float mMaxVelocity;
private float mMinVelocity;

private int mEdgeSize;
private int mTrackingEdges;

private ScrollerCompat mScroller;

private final Callback mCallback;

private View mCapturedView;
private boolean mReleaseInProgress;

private final ViewGroup mParentView;

/**
* A Callback is used as a communication channel with the ViewDragHelper back to the
* parent view using it. <code>on*</code>methods are invoked on siginficant events and several
* accessor methods are expected to provide the ViewDragHelper with more information
* about the state of the parent view upon request. The callback also makes decisions
* governing the range and draggability of child views.
*/
public static abstract class Callback {
/**
* Called when the drag state changes. See the <code>STATE_*</code> constants
* for more information.
*
* @param state The new drag state
*
* @see #STATE_IDLE
* @see #STATE_DRAGGING
* @see #STATE_SETTLING
*/
public void onViewDragStateChanged(int state) {}

/**
* Called when the captured view's position changes as the result of a drag or settle.
*
* @param changedView View whose position changed
* @param left New X coordinate of the left edge of the view
* @param top New Y coordinate of the top edge of the view
* @param dx Change in X position from the last call
* @param dy Change in Y position from the last call
*/
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {}

/**
* Called when a child view is captured for dragging or settling. The ID of the pointer
* currently dragging the captured view is supplied. If activePointerId is
* identified as {@link #INVALID_POINTER} the capture is programmatic instead of
* pointer-initiated.
*
* @param capturedChild Child view that was captured
* @param activePointerId Pointer id tracking the child capture
*/
public void onViewCaptured(View capturedChild, int activePointerId) {}

/**
* Called when the child view is no longer being actively dragged.
* The fling velocity is also supplied, if relevant. The velocity values may
* be clamped to system minimums or maximums.
*
* <p>Calling code may decide to fling or otherwise release the view to let it
* settle into place. It should do so using {@link #settleCapturedViewAt(int, int)}
* or {@link #flingCapturedView(int, int, int, int)}. If the Callback invokes
* one of these methods, the ViewDragHelper will enter {@link #STATE_SETTLING}
* and the view capture will not fully end until it comes to a complete stop.
* If neither of these methods is invoked before <code>onViewReleased</code> returns,
* the view will stop in place and the ViewDragHelper will return to
* {@link #STATE_IDLE}.</p>
*
* @param releasedChild The captured child view now being released
* @param xvel X velocity of the pointer as it left the screen in pixels per second.
* @param yvel Y velocity of the pointer as it left the screen in pixels per second.
*/
public void onViewReleased(View releasedChild, float xvel, float yvel) {}

/**
* Called when one of the subscribed edges in the parent view has been touched
* by the user while no child view is currently captured.
*
* @param edgeFlags A combination of edge flags describing the edge(s) currently touched
* @param pointerId ID of the pointer touching the described edge(s)
* @see #EDGE_LEFT
* @see #EDGE_TOP
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void onEdgeTouched(int edgeFlags, int pointerId) {}

/**
* Called when the given edge may become locked. This can happen if an edge drag
* was preliminarily rejected before beginning, but after {@link #onEdgeTouched(int, int)}
* was called. This method should return true to lock this edge or false to leave it
* unlocked. The default behavior is to leave edges unlocked.
*
* @param edgeFlags A combination of edge flags describing the edge(s) locked
* @return true to lock the edge, false to leave it unlocked
*/
public boolean onEdgeLock(int edgeFlags) {
return false;
}

/**
* Called when the user has started a deliberate drag away from one
* of the subscribed edges in the parent view while no child view is currently captured.
*
* @param edgeFlags A combination of edge flags describing the edge(s) dragged
* @param pointerId ID of the pointer touching the described edge(s)
* @see #EDGE_LEFT
* @see #EDGE_TOP
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void onEdgeDragStarted(int edgeFlags, int pointerId) {}

/**
* Called to determine the Z-order of child views.
*
* @param index the ordered position to query for
* @return index of the view that should be ordered at position <code>index</code>
*/
public int getOrderedChildIndex(int index) {
return index;
}

/**
* Return the magnitude of a draggable child view's horizontal range of motion in pixels.
* This method should return 0 for views that cannot move horizontally.
*
* @param child Child view to check
* @return range of horizontal motion in pixels
*/
public int getViewHorizontalDragRange(View child) {
return 0;
}

/**
* Return the magnitude of a draggable child view's vertical range of motion in pixels.
* This method should return 0 for views that cannot move vertically.
*
* @param child Child view to check
* @return range of vertical motion in pixels
*/
public int getViewVerticalDragRange(View child) {
return 0;
}

/**
* Called when the user's input indicates that they want to capture the given child view
* with the pointer indicated by pointerId. The callback should return true if the user
* is permitted to drag the given view with the indicated pointer.
*
* <p>ViewDragHelper may call this method multiple times for the same view even if
* the view is already captured; this indicates that a new pointer is trying to take
* control of the view.</p>
*
* <p>If this method returns true, a call to {@link #onViewCaptured(android.view.View, int)}
* will follow if the capture is successful.</p>
*
* @param child Child the user is attempting to capture
* @param pointerId ID of the pointer attempting the capture
* @return true if capture should be allowed, false otherwise
*/
public abstract boolean tryCaptureView(View child, int pointerId);

/**
* Restrict the motion of the dragged child view along the horizontal axis.
* The default implementation does not allow horizontal motion; the extending
* class must override this method and provide the desired clamping.
*
*
* @param child Child view being dragged
* @param left Attempted motion along the X axis
* @param dx Proposed change in position for left
* @return The new clamped position for left
*/
public int clampViewPositionHorizontal(View child, int left, int dx) {
return 0;
}

/**
* Restrict the motion of the dragged child view along the vertical axis.
* The default implementation does not allow vertical motion; the extending
* class must override this method and provide the desired clamping.
*
*
* @param child Child view being dragged
* @param top Attempted motion along the Y axis
* @param dy Proposed change in position for top
* @return The new clamped position for top
*/
public int clampViewPositionVertical(View child, int top, int dy) {
return 0;
}
}

/**
* Interpolator defining the animation curve for mScroller
*/
private static final Interpolator sInterpolator = new Interpolator() {
public float getInterpolation(float t) {
t -= 1.0f;
return t * t * t * t * t + 1.0f;
}
};

private final Runnable mSetIdleRunnable = new Runnable() {
public void run() {
setDragState(STATE_IDLE);
}
};

/**
* Factory method to create a new ViewDragHelper.
*
* @param forParent Parent view to monitor
* @param cb Callback to provide information and receive events
* @return a new ViewDragHelper instance
*/
public static ViewDragHelper create(ViewGroup forParent, Callback cb) {
return new ViewDragHelper(forParent.getContext(), forParent, cb);
}

/**
* Factory method to create a new ViewDragHelper.
*
* @param forParent Parent view to monitor
* @param sensitivity Multiplier for how sensitive the helper should be about detecting
*                    the start of a drag. Larger values are more sensitive. 1.0f is normal.
* @param cb Callback to provide information and receive events
* @return a new ViewDragHelper instance
*/
public static ViewDragHelper create(ViewGroup forParent, float sensitivity, Callback cb) {
final ViewDragHelper helper = create(forParent, cb);
helper.mTouchSlop = (int) (helper.mTouchSlop * (1 / sensitivity));
return helper;
}

/**
* Apps should use ViewDragHelper.create() to get a new instance.
* This will allow VDH to use internal compatibility implementations for different
* platform versions.
*
* @param context Context to initialize config-dependent params from
* @param forParent Parent view to monitor
*/
private ViewDragHelper(Context context, ViewGroup forParent, Callback cb) {
if (forParent == null) {
throw new IllegalArgumentException("Parent view may not be null");
}
if (cb == null) {
throw new IllegalArgumentException("Callback may not be null");
}

mParentView = forParent;
mCallback = cb;

final ViewConfiguration vc = ViewConfiguration.get(context);
final float density = context.getResources().getDisplayMetrics().density;
mEdgeSize = (int) (EDGE_SIZE * density + 0.5f);

mTouchSlop = vc.getScaledTouchSlop();
mMaxVelocity = vc.getScaledMaximumFlingVelocity();
mMinVelocity = vc.getScaledMinimumFlingVelocity();
mScroller = ScrollerCompat.create(context, sInterpolator);
}

/**
* Set the minimum velocity that will be detected as having a magnitude greater than zero
* in pixels per second. Callback methods accepting a velocity will be clamped appropriately.
*
* @param minVel Minimum velocity to detect
*/
public void setMinVelocity(float minVel) {
mMinVelocity = minVel;
}

/**
* Return the currently configured minimum velocity. Any flings with a magnitude less
* than this value in pixels per second. Callback methods accepting a velocity will receive
* zero as a velocity value if the real detected velocity was below this threshold.
*
* @return the minimum velocity that will be detected
*/
public float getMinVelocity() {
return mMinVelocity;
}

/**
* Retrieve the current drag state of this helper. This will return one of
* {@link #STATE_IDLE}, {@link #STATE_DRAGGING} or {@link #STATE_SETTLING}.
* @return The current drag state
*/
public int getViewDragState() {
return mDragState;
}

/**
* Enable edge tracking for the selected edges of the parent view.
* The callback's {@link Callback#onEdgeTouched(int, int)} and
* {@link Callback#onEdgeDragStarted(int, int)} methods will only be invoked
* for edges for which edge tracking has been enabled.
*
* @param edgeFlags Combination of edge flags describing the edges to watch
* @see #EDGE_LEFT
* @see #EDGE_TOP
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void setEdgeTrackingEnabled(int edgeFlags) {
mTrackingEdges = edgeFlags;
}

/**
* Return the size of an edge. This is the range in pixels along the edges of this view
* that will actively detect edge touches or drags if edge tracking is enabled.
*
* @return The size of an edge in pixels
* @see #setEdgeTrackingEnabled(int)
*/
public int getEdgeSize() {
return mEdgeSize;
}

/**
* Capture a specific child view for dragging within the parent. The callback will be notified
* but {@link Callback#tryCaptureView(android.view.View, int)} will not be asked permission to
* capture this view.
*
* @param childView Child view to capture
* @param activePointerId ID of the pointer that is dragging the captured child view
*/
public void captureChildView(View childView, int activePointerId) {
if (childView.getParent() != mParentView) {
throw new IllegalArgumentException("captureChildView: parameter must be a descendant " +
"of the ViewDragHelper's tracked parent view (" + mParentView + ")");
}

mCapturedView = childView;
mActivePointerId = activePointerId;
mCallback.onViewCaptured(childView, activePointerId);
setDragState(STATE_DRAGGING);
}

/**
* @return The currently captured view, or null if no view has been captured.
*/
public View getCapturedView() {
return mCapturedView;
}

/**
* @return The ID of the pointer currently dragging the captured view,
*         or {@link #INVALID_POINTER}.
*/
public int getActivePointerId() {
return mActivePointerId;
}

/**
* @return The minimum distance in pixels that the user must travel to initiate a drag
*/
public int getTouchSlop() {
return mTouchSlop;
}

/**
* The result of a call to this method is equivalent to
* {@link #processTouchEvent(android.view.MotionEvent)} receiving an ACTION_CANCEL event.
*/
public void cancel() {
mActivePointerId = INVALID_POINTER;
clearMotionHistory();

if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}

/**
* {@link #cancel()}, but also abort all motion in progress and snap to the end of any
* animation.
*/
public void abort() {
cancel();
if (mDragState == STATE_SETTLING) {
final int oldX = mScroller.getCurrX();
final int oldY = mScroller.getCurrY();
mScroller.abortAnimation();
final int newX = mScroller.getCurrX();
final int newY = mScroller.getCurrY();
mCallback.onViewPositionChanged(mCapturedView, newX, newY, newX - oldX, newY - oldY);
}
setDragState(STATE_IDLE);
}

/**
* Animate the view <code>child</code> to the given (left, top) position.
* If this method returns true, the caller should invoke {@link #continueSettling(boolean)}
* on each subsequent frame to continue the motion until it returns false. If this method
* returns false there is no further work to do to complete the movement.
*
* <p>This operation does not count as a capture event, though {@link #getCapturedView()}
* will still report the sliding view while the slide is in progress.</p>
*
* @param child Child view to capture and animate
* @param finalLeft Final left position of child
* @param finalTop Final top position of child
* @return true if animation should continue through {@link #continueSettling(boolean)} calls
*/
public boolean smoothSlideViewTo(View child, int finalLeft, int finalTop) {
mCapturedView = child;
mActivePointerId = INVALID_POINTER;

boolean continueSliding = forceSettleCapturedViewAt(finalLeft, finalTop, 0, 0);
if (!continueSliding && mDragState == STATE_IDLE && mCapturedView != null) {
// If we're in an IDLE state to begin with and aren't moving anywhere, we
// end up having a non-null capturedView with an IDLE dragState
mCapturedView = null;
}

return continueSliding;
}

/**
* Settle the captured view at the given (left, top) position.
* The appropriate velocity from prior motion will be taken into account.
* If this method returns true, the caller should invoke {@link #continueSettling(boolean)}
* on each subsequent frame to continue the motion until it returns false. If this method
* returns false there is no further work to do to complete the movement.
*
* @param finalLeft Settled left edge position for the captured view
* @param finalTop Settled top edge position for the captured view
* @return true if animation should continue through {@link #continueSettling(boolean)} calls
*/
public boolean settleCapturedViewAt(int finalLeft, int finalTop) {
if (!mReleaseInProgress) {
throw new IllegalStateException("Cannot settleCapturedViewAt outside of a call to " +
"Callback#onViewReleased");
}

return forceSettleCapturedViewAt(finalLeft, finalTop,
(int) VelocityTrackerCompat.getXVelocity(mVelocityTracker, mActivePointerId),
(int) VelocityTrackerCompat.getYVelocity(mVelocityTracker, mActivePointerId));
}

/**
* Settle the captured view at the given (left, top) position.
*
* @param finalLeft Target left position for the captured view
* @param finalTop Target top position for the captured view
* @param xvel Horizontal velocity
* @param yvel Vertical velocity
* @return true if animation should continue through {@link #continueSettling(boolean)} calls
*/
private boolean forceSettleCapturedViewAt(int finalLeft, int finalTop, int xvel, int yvel) {
final int startLeft = mCapturedView.getLeft();
final int startTop = mCapturedView.getTop();
final int dx = finalLeft - startLeft;
final int dy = finalTop - startTop;

if (dx == 0 && dy == 0) {
// Nothing to do. Send callbacks, be done.
mScroller.abortAnimation();
setDragState(STATE_IDLE);
return false;
}

final int duration = computeSettleDuration(mCapturedView, dx, dy, xvel, yvel);
mScroller.startScroll(startLeft, startTop, dx, dy, duration);

setDragState(STATE_SETTLING);
return true;
}

private int computeSettleDuration(View child, int dx, int dy, int xvel, int yvel) {
xvel = clampMag(xvel, (int) mMinVelocity, (int) mMaxVelocity);
yvel = clampMag(yvel, (int) mMinVelocity, (int) mMaxVelocity);
final int absDx = Math.abs(dx);
final int absDy = Math.abs(dy);
final int absXVel = Math.abs(xvel);
final int absYVel = Math.abs(yvel);
final int addedVel = absXVel + absYVel;
final int addedDistance = absDx + absDy;

final float xweight = xvel != 0 ? (float) absXVel / addedVel :
(float) absDx / addedDistance;
final float yweight = yvel != 0 ? (float) absYVel / addedVel :
(float) absDy / addedDistance;

int xduration = computeAxisDuration(dx, xvel, mCallback.getViewHorizontalDragRange(child));
int yduration = computeAxisDuration(dy, yvel, mCallback.getViewVerticalDragRange(child));

return (int) (xduration * xweight + yduration * yweight);
}

private int computeAxisDuration(int delta, int velocity, int motionRange) {
if (delta == 0) {
return 0;
}

final int width = mParentView.getWidth();
final int halfWidth = width / 2;
final float distanceRatio = Math.min(1f, (float) Math.abs(delta) / width);
final float distance = halfWidth + halfWidth *
distanceInfluenceForSnapDuration(distanceRatio);

int duration;
velocity = Math.abs(velocity);
if (velocity > 0) {
duration = 4 * Math.round(1000 * Math.abs(distance / velocity));
} else {
final float range = (float) Math.abs(delta) / motionRange;
duration = (int) ((range + 1) * BASE_SETTLE_DURATION);
}
return Math.min(duration, MAX_SETTLE_DURATION);
}

/**
* Clamp the magnitude of value for absMin and absMax.
* If the value is below the minimum, it will be clamped to zero.
* If the value is above the maximum, it will be clamped to the maximum.
*
* @param value Value to clamp
* @param absMin Absolute value of the minimum significant value to return
* @param absMax Absolute value of the maximum value to return
* @return The clamped value with the same sign as <code>value</code>
*/
private int clampMag(int value, int absMin, int absMax) {
final int absValue = Math.abs(value);
if (absValue < absMin) return 0;
if (absValue > absMax) return value > 0 ? absMax : -absMax;
return value;
}

/**
* Clamp the magnitude of value for absMin and absMax.
* If the value is below the minimum, it will be clamped to zero.
* If the value is above the maximum, it will be clamped to the maximum.
*
* @param value Value to clamp
* @param absMin Absolute value of the minimum significant value to return
* @param absMax Absolute value of the maximum value to return
* @return The clamped value with the same sign as <code>value</code>
*/
private float clampMag(float value, float absMin, float absMax) {
final float absValue = Math.abs(value);
if (absValue < absMin) return 0;
if (absValue > absMax) return value > 0 ? absMax : -absMax;
return value;
}

private float distanceInfluenceForSnapDuration(float f) {
f -= 0.5f; // center the values about 0.
f *= 0.3f * Math.PI / 2.0f;
return (float) Math.sin(f);
}

/**
* Settle the captured view based on standard free-moving fling behavior.
* The caller should invoke {@link #continueSettling(boolean)} on each subsequent frame
* to continue the motion until it returns false.
*
* @param minLeft Minimum X position for the view's left edge
* @param minTop Minimum Y position for the view's top edge
* @param maxLeft Maximum X position for the view's left edge
* @param maxTop Maximum Y position for the view's top edge
*/
public void flingCapturedView(int minLeft, int minTop, int maxLeft, int maxTop) {
if (!mReleaseInProgress) {
throw new IllegalStateException("Cannot flingCapturedView outside of a call to " +
"Callback#onViewReleased");
}

mScroller.fling(mCapturedView.getLeft(), mCapturedView.getTop(),
(int) VelocityTrackerCompat.getXVelocity(mVelocityTracker, mActivePointerId),
(int) VelocityTrackerCompat.getYVelocity(mVelocityTracker, mActivePointerId),
minLeft, maxLeft, minTop, maxTop);

setDragState(STATE_SETTLING);
}

/**
* Move the captured settling view by the appropriate amount for the current time.
* If <code>continueSettling</code> returns true, the caller should call it again
* on the next frame to continue.
*
* @param deferCallbacks true if state callbacks should be deferred via posted message.
*                       Set this to true if you are calling this method from
*                       {@link android.view.View#computeScroll()} or similar methods
*                       invoked as part of layout or drawing.
* @return true if settle is still in progress
*/
public boolean continueSettling(boolean deferCallbacks) {
if (mDragState == STATE_SETTLING) {
boolean keepGoing = mScroller.computeScrollOffset();
final int x = mScroller.getCurrX();
final int y = mScroller.getCurrY();
final int dx = x - mCapturedView.getLeft();
final int dy = y - mCapturedView.getTop();

if (dx != 0) {
ViewCompat.offsetLeftAndRight(mCapturedView, dx);
}
if (dy != 0) {
ViewCompat.offsetTopAndBottom(mCapturedView, dy);
}

if (dx != 0 || dy != 0) {
mCallback.onViewPositionChanged(mCapturedView, x, y, dx, dy);
}

if (keepGoing && x == mScroller.getFinalX() && y == mScroller.getFinalY()) {
// Close enough. The interpolator/scroller might think we're still moving
// but the user sure doesn't.
mScroller.abortAnimation();
keepGoing = false;
}

if (!keepGoing) {
if (deferCallbacks) {
mParentView.post(mSetIdleRunnable);
} else {
setDragState(STATE_IDLE);
}
}
}

return mDragState == STATE_SETTLING;
}

/**
* Like all callback events this must happen on the UI thread, but release
* involves some extra semantics. During a release (mReleaseInProgress)
* is the only time it is valid to call {@link #settleCapturedViewAt(int, int)}
* or {@link #flingCapturedView(int, int, int, int)}.
*/
private void dispatchViewReleased(float xvel, float yvel) {
mReleaseInProgress = true;
mCallback.onViewReleased(mCapturedView, xvel, yvel);
mReleaseInProgress = false;

if (mDragState == STATE_DRAGGING) {
// onViewReleased didn't call a method that would have changed this. Go idle.
setDragState(STATE_IDLE);
}
}

private void clearMotionHistory() {
if (mInitialMotionX == null) {
return;
}
Arrays.fill(mInitialMotionX, 0);
Arrays.fill(mInitialMotionY, 0);
Arrays.fill(mLastMotionX, 0);
Arrays.fill(mLastMotionY, 0);
Arrays.fill(mInitialEdgesTouched, 0);
Arrays.fill(mEdgeDragsInProgress, 0);
Arrays.fill(mEdgeDragsLocked, 0);
mPointersDown = 0;
}

private void clearMotionHistory(int pointerId) {
if (mInitialMotionX == null) {
return;
}
mInitialMotionX[pointerId] = 0;
mInitialMotionY[pointerId] = 0;
mLastMotionX[pointerId] = 0;
mLastMotionY[pointerId] = 0;
mInitialEdgesTouched[pointerId] = 0;
mEdgeDragsInProgress[pointerId] = 0;
mEdgeDragsLocked[pointerId] = 0;
mPointersDown &= ~(1 << pointerId);
}

private void ensureMotionHistorySizeForId(int pointerId) {
if (mInitialMotionX == null || mInitialMotionX.length <= pointerId) {
float[] imx = new float[pointerId + 1];
float[] imy = new float[pointerId + 1];
float[] lmx = new float[pointerId + 1];
float[] lmy = new float[pointerId + 1];
int[] iit = new int[pointerId + 1];
int[] edip = new int[pointerId + 1];
int[] edl = new int[pointerId + 1];

if (mInitialMotionX != null) {
System.arraycopy(mInitialMotionX, 0, imx, 0, mInitialMotionX.length);
System.arraycopy(mInitialMotionY, 0, imy, 0, mInitialMotionY.length);
System.arraycopy(mLastMotionX, 0, lmx, 0, mLastMotionX.length);
System.arraycopy(mLastMotionY, 0, lmy, 0, mLastMotionY.length);
System.arraycopy(mInitialEdgesTouched, 0, iit, 0, mInitialEdgesTouched.length);
System.arraycopy(mEdgeDragsInProgress, 0, edip, 0, mEdgeDragsInProgress.length);
System.arraycopy(mEdgeDragsLocked, 0, edl, 0, mEdgeDragsLocked.length);
}

mInitialMotionX = imx;
mInitialMotionY = imy;
mLastMotionX = lmx;
mLastMotionY = lmy;
mInitialEdgesTouched = iit;
mEdgeDragsInProgress = edip;
mEdgeDragsLocked = edl;
}
}

private void saveInitialMotion(float x, float y, int pointerId) {
ensureMotionHistorySizeForId(pointerId);
mInitialMotionX[pointerId] = mLastMotionX[pointerId] = x;
mInitialMotionY[pointerId] = mLastMotionY[pointerId] = y;
mInitialEdgesTouched[pointerId] = getEdgesTouched((int) x, (int) y);
mPointersDown |= 1 << pointerId;
}

private void saveLastMotion(MotionEvent ev) {
final int pointerCount = MotionEventCompat.getPointerCount(ev);
for (int i = 0; i < pointerCount; i++) {
final int pointerId = MotionEventCompat.getPointerId(ev, i);
final float x = MotionEventCompat.getX(ev, i);
final float y = MotionEventCompat.getY(ev, i);
mLastMotionX[pointerId] = x;
mLastMotionY[pointerId] = y;
}
}

/**
* Check if the given pointer ID represents a pointer that is currently down (to the best
* of the ViewDragHelper's knowledge).
*
* <p>The state used to report this information is populated by the methods
* {@link #shouldInterceptTouchEvent(android.view.MotionEvent)} or
* {@link #processTouchEvent(android.view.MotionEvent)}. If one of these methods has not
* been called for all relevant MotionEvents to track, the information reported
* by this method may be stale or incorrect.</p>
*
* @param pointerId pointer ID to check; corresponds to IDs provided by MotionEvent
* @return true if the pointer with the given ID is still down
*/
public boolean isPointerDown(int pointerId) {
return (mPointersDown & 1 << pointerId) != 0;
}

void setDragState(int state) {
mParentView.removeCallbacks(mSetIdleRunnable);
if (mDragState != state) {
mDragState = state;
mCallback.onViewDragStateChanged(state);
if (mDragState == STATE_IDLE) {
mCapturedView = null;
}
}
}

/**
* Attempt to capture the view with the given pointer ID. The callback will be involved.
* This will put us into the "dragging" state. If we've already captured this view with
* this pointer this method will immediately return true without consulting the callback.
*
* @param toCapture View to capture
* @param pointerId Pointer to capture with
* @return true if capture was successful
*/
boolean tryCaptureViewForDrag(View toCapture, int pointerId) {
if (toCapture == mCapturedView && mActivePointerId == pointerId) {
// Already done!
return true;
}
if (toCapture != null && mCallback.tryCaptureView(toCapture, pointerId)) {
mActivePointerId = pointerId;
captureChildView(toCapture, pointerId);
return true;
}
return false;
}

/**
* Tests scrollability within child views of v given a delta of dx.
*
* @param v View to test for horizontal scrollability
* @param checkV Whether the view v passed should itself be checked for scrollability (true),
*               or just its children (false).
* @param dx Delta scrolled in pixels along the X axis
* @param dy Delta scrolled in pixels along the Y axis
* @param x X coordinate of the active touch point
* @param y Y coordinate of the active touch point
* @return true if child views of v can be scrolled by delta of dx.
*/
protected boolean canScroll(View v, boolean checkV, int dx, int dy, int x, int y) {
if (v instanceof ViewGroup) {
final ViewGroup group = (ViewGroup) v;
final int scrollX = v.getScrollX();
final int scrollY = v.getScrollY();
final int count = group.getChildCount();
// Count backwards - let topmost views consume scroll distance first.
for (int i = count - 1; i >= 0; i--) {
// TODO: Add versioned support here for transformed views.
// This will not work for transformed views in Honeycomb+
final View child = group.getChildAt(i);
if (x + scrollX >= child.getLeft() && x + scrollX < child.getRight() &&
y + scrollY >= child.getTop() && y + scrollY < child.getBottom() &&
canScroll(child, true, dx, dy, x + scrollX - child.getLeft(),
y + scrollY - child.getTop())) {
return true;
}
}
}

return checkV && (ViewCompat.canScrollHorizontally(v, -dx) ||
ViewCompat.canScrollVertically(v, -dy));
}

/**
* Check if this event as provided to the parent view's onInterceptTouchEvent should
* cause the parent to intercept the touch event stream.
*
* @param ev MotionEvent provided to onInterceptTouchEvent
* @return true if the parent view should return true from onInterceptTouchEvent
*/
public boolean shouldInterceptTouchEvent(MotionEvent ev) {
final int action = MotionEventCompat.getActionMasked(ev);
final int actionIndex = MotionEventCompat.getActionIndex(ev);

if (action == MotionEvent.ACTION_DOWN) {
// Reset things for a new event stream, just in case we didn't get
// the whole previous stream.
cancel();
}

if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);

switch (action) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
final int pointerId = MotionEventCompat.getPointerId(ev, 0);
saveInitialMotion(x, y, pointerId);

final View toCapture = findTopChildUnder((int) x, (int) y);

// Catch a settling view if possible.
if (toCapture == mCapturedView && mDragState == STATE_SETTLING) {
tryCaptureViewForDrag(toCapture, pointerId);
}

final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
break;
}

case MotionEventCompat.ACTION_POINTER_DOWN: {
final int pointerId = MotionEventCompat.getPointerId(ev, actionIndex);
final float x = MotionEventCompat.getX(ev, actionIndex);
final float y = MotionEventCompat.getY(ev, actionIndex);

saveInitialMotion(x, y, pointerId);

// A ViewDragHelper can only manipulate one view at a time.
if (mDragState == STATE_IDLE) {
final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
} else if (mDragState == STATE_SETTLING) {
// Catch a settling view if possible.
final View toCapture = findTopChildUnder((int) x, (int) y);
if (toCapture == mCapturedView) {
tryCaptureViewForDrag(toCapture, pointerId);
}
}
break;
}

case MotionEvent.ACTION_MOVE: {
if (mInitialMotionX == null || mInitialMotionY == null) break;

// First to cross a touch slop over a draggable view wins. Also report edge drags.
final int pointerCount = MotionEventCompat.getPointerCount(ev);
for (int i = 0; i < pointerCount; i++) {
final int pointerId = MotionEventCompat.getPointerId(ev, i);

// If pointer is invalid then skip the ACTION_MOVE.
if (!isValidPointerForActionMove(pointerId)) continue;

final float x = MotionEventCompat.getX(ev, i);
final float y = MotionEventCompat.getY(ev, i);
final float dx = x - mInitialMotionX[pointerId];
final float dy = y - mInitialMotionY[pointerId];

final View toCapture = findTopChildUnder((int) x, (int) y);
final boolean pastSlop = toCapture != null && checkTouchSlop(toCapture, dx, dy);
if (pastSlop) {
// check the callback's
// getView[Horizontal|Vertical]DragRange methods to know
// if you can move at all along an axis, then see if it
// would clamp to the same value. If you can't move at
// all in every dimension with a nonzero range, bail.
final int oldLeft = toCapture.getLeft();
final int targetLeft = oldLeft + (int) dx;
final int newLeft = mCallback.clampViewPositionHorizontal(toCapture,
targetLeft, (int) dx);
final int oldTop = toCapture.getTop();
final int targetTop = oldTop + (int) dy;
final int newTop = mCallback.clampViewPositionVertical(toCapture, targetTop,
(int) dy);
final int horizontalDragRange = mCallback.getViewHorizontalDragRange(
toCapture);
final int verticalDragRange = mCallback.getViewVerticalDragRange(toCapture);
if ((horizontalDragRange == 0 || horizontalDragRange > 0
&& newLeft == oldLeft) && (verticalDragRange == 0
|| verticalDragRange > 0 && newTop == oldTop)) {
break;
}
}
reportNewEdgeDrags(dx, dy, pointerId);
if (mDragState == STATE_DRAGGING) {
// Callback might have started an edge drag
break;
}

if (pastSlop && tryCaptureViewForDrag(toCapture, pointerId)) {
break;
}
}
saveLastMotion(ev);
break;
}

case MotionEventCompat.ACTION_POINTER_UP: {
final int pointerId = MotionEventCompat.getPointerId(ev, actionIndex);
clearMotionHistory(pointerId);
break;
}

case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL: {
cancel();
break;
}
}

return mDragState == STATE_DRAGGING;
}

/**
* Process a touch event received by the parent view. This method will dispatch callback events
* as needed before returning. The parent view's onTouchEvent implementation should call this.
*
* @param ev The touch event received by the parent view
*/
public void processTouchEvent(MotionEvent ev) {
final int action = MotionEventCompat.getActionMasked(ev);
final int actionIndex = MotionEventCompat.getActionIndex(ev);

if (action == MotionEvent.ACTION_DOWN) {
// Reset things for a new event stream, just in case we didn't get
// the whole previous stream.
cancel();
}

if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);

switch (action) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
final int pointerId = MotionEventCompat.getPointerId(ev, 0);
final View toCapture = findTopChildUnder((int) x, (int) y);

saveInitialMotion(x, y, pointerId);

// Since the parent is already directly processing this touch event,
// there is no reason to delay for a slop before dragging.
// Start immediately if possible.
tryCaptureViewForDrag(toCapture, pointerId);

final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
break;
}

case MotionEventCompat.ACTION_POINTER_DOWN: {
final int pointerId = MotionEventCompat.getPointerId(ev, actionIndex);
final float x = MotionEventCompat.getX(ev, actionIndex);
final float y = MotionEventCompat.getY(ev, actionIndex);

saveInitialMotion(x, y, pointerId);

// A ViewDragHelper can only manipulate one view at a time.
if (mDragState == STATE_IDLE) {
// If we're idle we can do anything! Treat it like a normal down event.

final View toCapture = findTopChildUnder((int) x, (int) y);
tryCaptureViewForDrag(toCapture, pointerId);

final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
} else if (isCapturedViewUnder((int) x, (int) y)) {
// We're still tracking a captured view. If the same view is under this
// point, we'll swap to controlling it with this pointer instead.
// (This will still work if we're "catching" a settling view.)

tryCaptureViewForDrag(mCapturedView, pointerId);
}
break;
}

case MotionEvent.ACTION_MOVE: {
if (mDragState == STATE_DRAGGING) {
// If pointer is invalid then skip the ACTION_MOVE.
if (!isValidPointerForActionMove(mActivePointerId)) break;

final int index = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
final float x = MotionEventCompat.getX(ev, index);
final float y = MotionEventCompat.getY(ev, index);
final int idx = (int) (x - mLastMotionX[mActivePointerId]);
final int idy = (int) (y - mLastMotionY[mActivePointerId]);

dragTo(mCapturedView.getLeft() + idx, mCapturedView.getTop() + idy, idx, idy);

saveLastMotion(ev);
} else {
// Check to see if any pointer is now over a draggable view.
final int pointerCount = MotionEventCompat.getPointerCount(ev);
for (int i = 0; i < pointerCount; i++) {
final int pointerId = MotionEventCompat.getPointerId(ev, i);

// If pointer is invalid then skip the ACTION_MOVE.
if (!isValidPointerForActionMove(pointerId)) continue;

final float x = MotionEventCompat.getX(ev, i);
final float y = MotionEventCompat.getY(ev, i);
final float dx = x - mInitialMotionX[pointerId];
final float dy = y - mInitialMotionY[pointerId];

reportNewEdgeDrags(dx, dy, pointerId);
if (mDragState == STATE_DRAGGING) {
// Callback might have started an edge drag.
break;
}

final View toCapture = findTopChildUnder((int) x, (int) y);
if (checkTouchSlop(toCapture, dx, dy) &&
tryCaptureViewForDrag(toCapture, pointerId)) {
break;
}
}
saveLastMotion(ev);
}
break;
}

case MotionEventCompat.ACTION_POINTER_UP: {
final int pointerId = MotionEventCompat.getPointerId(ev, actionIndex);
if (mDragState == STATE_DRAGGING && pointerId == mActivePointerId) {
// Try to find another pointer that's still holding on to the captured view.
int newActivePointer = INVALID_POINTER;
final int pointerCount = MotionEventCompat.getPointerCount(ev);
for (int i = 0; i < pointerCount; i++) {
final int id = MotionEventCompat.getPointerId(ev, i);
if (id == mActivePointerId) {
// This one's going away, skip.
continue;
}

final float x = MotionEventCompat.getX(ev, i);
final float y = MotionEventCompat.getY(ev, i);
if (findTopChildUnder((int) x, (int) y) == mCapturedView &&
tryCaptureViewForDrag(mCapturedView, id)) {
newActivePointer = mActivePointerId;
break;
}
}

if (newActivePointer == INVALID_POINTER) {
// We didn't find another pointer still touching the view, release it.
releaseViewForPointerUp();
}
}
clearMotionHistory(pointerId);
break;
}

case MotionEvent.ACTION_UP: {
if (mDragState == STATE_DRAGGING) {
releaseViewForPointerUp();
}
cancel();
break;
}

case MotionEvent.ACTION_CANCEL: {
if (mDragState == STATE_DRAGGING) {
dispatchViewReleased(0, 0);
}
cancel();
break;
}
}
}

private void reportNewEdgeDrags(float dx, float dy, int pointerId) {
int dragsStarted = 0;
if (checkNewEdgeDrag(dx, dy, pointerId, EDGE_LEFT)) {
dragsStarted |= EDGE_LEFT;
}
if (checkNewEdgeDrag(dy, dx, pointerId, EDGE_TOP)) {
dragsStarted |= EDGE_TOP;
}
if (checkNewEdgeDrag(dx, dy, pointerId, EDGE_RIGHT)) {
dragsStarted |= EDGE_RIGHT;
}
if (checkNewEdgeDrag(dy, dx, pointerId, EDGE_BOTTOM)) {
dragsStarted |= EDGE_BOTTOM;
}

if (dragsStarted != 0) {
mEdgeDragsInProgress[pointerId] |= dragsStarted;
mCallback.onEdgeDragStarted(dragsStarted, pointerId);
}
}

private boolean checkNewEdgeDrag(float delta, float odelta, int pointerId, int edge) {
final float absDelta = Math.abs(delta);
final float absODelta = Math.abs(odelta);

if ((mInitialEdgesTouched[pointerId] & edge) != edge  || (mTrackingEdges & edge) == 0 ||
(mEdgeDragsLocked[pointerId] & edge) == edge ||
(mEdgeDragsInProgress[pointerId] & edge) == edge ||
(absDelta <= mTouchSlop && absODelta <= mTouchSlop)) {
return false;
}
if (absDelta < absODelta * 0.5f && mCallback.onEdgeLock(edge)) {
mEdgeDragsLocked[pointerId] |= edge;
return false;
}
return (mEdgeDragsInProgress[pointerId] & edge) == 0 && absDelta > mTouchSlop;
}

/**
* Check if we've crossed a reasonable touch slop for the given child view.
* If the child cannot be dragged along the horizontal or vertical axis, motion
* along that axis will not count toward the slop check.
*
* @param child Child to check
* @param dx Motion since initial position along X axis
* @param dy Motion since initial position along Y axis
* @return true if the touch slop has been crossed
*/
private boolean checkTouchSlop(View child, float dx, float dy) {
if (child == null) {
return false;
}
final boolean checkHorizontal = mCallback.getViewHorizontalDragRange(child) > 0;
final boolean checkVertical = mCallback.getViewVerticalDragRange(child) > 0;

if (checkHorizontal && checkVertical) {
return dx * dx + dy * dy > mTouchSlop * mTouchSlop;
} else if (checkHorizontal) {
return Math.abs(dx) > mTouchSlop;
} else if (checkVertical) {
return Math.abs(dy) > mTouchSlop;
}
return false;
}

/**
* Check if any pointer tracked in the current gesture has crossed
* the required slop threshold.
*
* <p>This depends on internal state populated by
* {@link #shouldInterceptTouchEvent(android.view.MotionEvent)} or
* {@link #processTouchEvent(android.view.MotionEvent)}. You should only rely on
* the results of this method after all currently available touch data
* has been provided to one of these two methods.</p>
*
* @param directions Combination of direction flags, see {@link #DIRECTION_HORIZONTAL},
*                   {@link #DIRECTION_VERTICAL}, {@link #DIRECTION_ALL}
* @return true if the slop threshold has been crossed, false otherwise
*/
public boolean checkTouchSlop(int directions) {
final int count = mInitialMotionX.length;
for (int i = 0; i < count; i++) {
if (checkTouchSlop(directions, i)) {
return true;
}
}
return false;
}

/**
* Check if the specified pointer tracked in the current gesture has crossed
* the required slop threshold.
*
* <p>This depends on internal state populated by
* {@link #shouldInterceptTouchEvent(android.view.MotionEvent)} or
* {@link #processTouchEvent(android.view.MotionEvent)}. You should only rely on
* the results of this method after all currently available touch data
* has been provided to one of these two methods.</p>
*
* @param directions Combination of direction flags, see {@link #DIRECTION_HORIZONTAL},
*                   {@link #DIRECTION_VERTICAL}, {@link #DIRECTION_ALL}
* @param pointerId ID of the pointer to slop check as specified by MotionEvent
* @return true if the slop threshold has been crossed, false otherwise
*/
public boolean checkTouchSlop(int directions, int pointerId) {
if (!isPointerDown(pointerId)) {
return false;
}

final boolean checkHorizontal = (directions & DIRECTION_HORIZONTAL) == DIRECTION_HORIZONTAL;
final boolean checkVertical = (directions & DIRECTION_VERTICAL) == DIRECTION_VERTICAL;

final float dx = mLastMotionX[pointerId] - mInitialMotionX[pointerId];
final float dy = mLastMotionY[pointerId] - mInitialMotionY[pointerId];

if (checkHorizontal && checkVertical) {
return dx * dx + dy * dy > mTouchSlop * mTouchSlop;
} else if (checkHorizontal) {
return Math.abs(dx) > mTouchSlop;
} else if (checkVertical) {
return Math.abs(dy) > mTouchSlop;
}
return false;
}

/**
* Check if any of the edges specified were initially touched in the currently active gesture.
* If there is no currently active gesture this method will return false.
*
* @param edges Edges to check for an initial edge touch. See {@link #EDGE_LEFT},
*              {@link #EDGE_TOP}, {@link #EDGE_RIGHT}, {@link #EDGE_BOTTOM} and
*              {@link #EDGE_ALL}
* @return true if any of the edges specified were initially touched in the current gesture
*/
public boolean isEdgeTouched(int edges) {
final int count = mInitialEdgesTouched.length;
for (int i = 0; i < count; i++) {
if (isEdgeTouched(edges, i)) {
return true;
}
}
return false;
}

/**
* Check if any of the edges specified were initially touched by the pointer with
* the specified ID. If there is no currently active gesture or if there is no pointer with
* the given ID currently down this method will return false.
*
* @param edges Edges to check for an initial edge touch. See {@link #EDGE_LEFT},
*              {@link #EDGE_TOP}, {@link #EDGE_RIGHT}, {@link #EDGE_BOTTOM} and
*              {@link #EDGE_ALL}
* @return true if any of the edges specified were initially touched in the current gesture
*/
public boolean isEdgeTouched(int edges, int pointerId) {
return isPointerDown(pointerId) && (mInitialEdgesTouched[pointerId] & edges) != 0;
}

private void releaseViewForPointerUp() {
mVelocityTracker.computeCurrentVelocity(1000, mMaxVelocity);
final float xvel = clampMag(
VelocityTrackerCompat.getXVelocity(mVelocityTracker, mActivePointerId),
mMinVelocity, mMaxVelocity);
final float yvel = clampMag(
VelocityTrackerCompat.getYVelocity(mVelocityTracker, mActivePointerId),
mMinVelocity, mMaxVelocity);
dispatchViewReleased(xvel, yvel);
}

private void dragTo(int left, int top, int dx, int dy) {
int clampedX = left;
int clampedY = top;
final int oldLeft = mCapturedView.getLeft();
final int oldTop = mCapturedView.getTop();
if (dx != 0) {
clampedX = mCallback.clampViewPositionHorizontal(mCapturedView, left, dx);
ViewCompat.offsetLeftAndRight(mCapturedView, clampedX - oldLeft);
}
if (dy != 0) {
clampedY = mCallback.clampViewPositionVertical(mCapturedView, top, dy);
ViewCompat.offsetTopAndBottom(mCapturedView, clampedY - oldTop);
}

if (dx != 0 || dy != 0) {
final int clampedDx = clampedX - oldLeft;
final int clampedDy = clampedY - oldTop;
mCallback.onViewPositionChanged(mCapturedView, clampedX, clampedY,
clampedDx, clampedDy);
}
}

/**
* Determine if the currently captured view is under the given point in the
* parent view's coordinate system. If there is no captured view this method
* will return false.
*
* @param x X position to test in the parent's coordinate system
* @param y Y position to test in the parent's coordinate system
* @return true if the captured view is under the given point, false otherwise
*/
public boolean isCapturedViewUnder(int x, int y) {
return isViewUnder(mCapturedView, x, y);
}

/**
* Determine if the supplied view is under the given point in the
* parent view's coordinate system.
*
* @param view Child view of the parent to hit test
* @param x X position to test in the parent's coordinate system
* @param y Y position to test in the parent's coordinate system
* @return true if the supplied view is under the given point, false otherwise
*/
public boolean isViewUnder(View view, int x, int y) {
if (view == null) {
return false;
}
return x >= view.getLeft() &&
x < view.getRight() &&
y >= view.getTop() &&
y < view.getBottom();
}

/**
* Find the topmost child under the given point within the parent view's coordinate system.
* The child order is determined using {@link Callback#getOrderedChildIndex(int)}.
*
* @param x X position to test in the parent's coordinate system
* @param y Y position to test in the parent's coordinate system
* @return The topmost child view under (x, y) or null if none found.
*/
public View findTopChildUnder(int x, int y) {
final int childCount = mParentView.getChildCount();
for (int i = childCount - 1; i >= 0; i--) {
final View child = mParentView.getChildAt(mCallback.getOrderedChildIndex(i));
if (x >= child.getLeft() && x < child.getRight() &&
y >= child.getTop() && y < child.getBottom()) {
return child;
}
}
return null;
}

private int getEdgesTouched(int x, int y) {
int result = 0;

if (x < mParentView.getLeft() + mEdgeSize) result |= EDGE_LEFT;
if (y < mParentView.getTop() + mEdgeSize) result |= EDGE_TOP;
if (x > mParentView.getRight() - mEdgeSize) result |= EDGE_RIGHT;
if (y > mParentView.getBottom() - mEdgeSize) result |= EDGE_BOTTOM;

return result;
}

private boolean isValidPointerForActionMove(int pointerId) {
if (!isPointerDown(pointerId)) {
Log.e(TAG, "Ignoring pointerId=" + pointerId + " because ACTION_DOWN was not received "
+ "for this pointer before ACTION_MOVE. It likely happened because "
+ " ViewDragHelper did not receive all the events in the event stream.");
return false;
}
return true;
}
}

仔细查看ViewDragHelper的源码，在Callback这个回调接口类里面有一个回调方法：onViewDragStateChanged(int state)，看起来很有道理的样子，我们试试吧。

state有三种状态：

STATE_IDLE：view不拖拽状态；

STATE_DRAGGING：view拖拽中；

STATE_SETTLING：view设置中。

当然，这几种状态必然也会引起UI的绘制，正好，我们就需要具备这个条件的方法。试试效果如何吧。

当我们兴致勃勃的在不同状态中写好逻辑时，我们发现每次拖拽view之后，view都会回到初始的位置，背景是改变了，但是不是我先期望的结果。第二猜想破产。

这可如何是好？我们看看有没有其他办法吧。

第一时间，我想到的是“生命周期”，每错，就像activity一样，callback的回调也应该是有顺序的：

12-15 14:41:18.828  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:18.828  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:18.845  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:18.845  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:18.862  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:18.862  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:18.878  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:18.878  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:18.895  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:18.895  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:18.912  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:18.912  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:18.928  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:18.929  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:18.929  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:18.929  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:18.929  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:18.929  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:18.929  19489-19489/com.baimi.wallet D/bmzg﹕ tryCaptureView
12-15 14:41:18.929  19489-19489/com.baimi.wallet D/bmzg﹕ onViewCaptured
12-15 14:41:18.929  19489-19489/com.baimi.wallet D/bmzg﹕ onViewDragStateChanged
12-15 14:41:18.945  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:18.945  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:18.945  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:18.962  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:18.962  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:18.962  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:18.978  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:18.979  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:18.979  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:18.996  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:18.996  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:18.996  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.012  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.012  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.012  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.029  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.029  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.029  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.046  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.047  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.047  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.062  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.063  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.063  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.079  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.079  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.079  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.096  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.096  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.096  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.113  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.113  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.113  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.129  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.130  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.130  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.146  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.146  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.146  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.162  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.163  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.163  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.179  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.179  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.179  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.197  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.197  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.197  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.212  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.213  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.213  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.229  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.229  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.229  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.246  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.246  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.246  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.262  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.263  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.263  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.279  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.279  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.279  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.296  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.297  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.297  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.313  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.313  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.313  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.330  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.330  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.330  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.346  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.346  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.346  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.363  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.363  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.363  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.379  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.380  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.380  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.396  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.397  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.397  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.413  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.413  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.413  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.429  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.429  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.429  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.446  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.446  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.446  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.463  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.464  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.464  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.479  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.480  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.480  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.496  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.496  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:19.496  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.513  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.513  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.529  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:19.530  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.539  19489-19489/com.baimi.wallet D/bmzg﹕ onViewReleased
12-15 14:41:19.539  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:19.541  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:19.541  19489-19489/com.baimi.wallet D/bmzg﹕ onViewDragStateChanged
12-15 14:41:19.548  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.563  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.579  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.596  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.613  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.630  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.646  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.663  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.680  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.696  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.713  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.730  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.746  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.763  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.780  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.797  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.830  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.863  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.913  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:19.930  19489-19489/com.baimi.wallet D/bmzg﹕ onViewDragStateChanged
12-15 14:41:27.944  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:27.944  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:27.961  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:27.961  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:27.977  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:27.978  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:27.994  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:27.994  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ tryCaptureView
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ onViewCaptured
12-15 14:41:28.011  19489-19489/com.baimi.wallet D/bmzg﹕ onViewDragStateChanged
12-15 14:41:28.028  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.028  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.044  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.045  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.045  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.061  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.061  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.078  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.078  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.078  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.094  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.094  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.117  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.117  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.117  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.134  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.134  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.134  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.150  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.151  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.151  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.167  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.167  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.167  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.184  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.184  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.184  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.200  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.200  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.200  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.217  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.217  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.217  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.234  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.234  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.234  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.251  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.251  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.251  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.267  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionHorizontal
12-15 14:41:28.267  19489-19489/com.baimi.wallet D/bmzg﹕ clampViewPositionVertical
12-15 14:41:28.268  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.275  19489-19489/com.baimi.wallet D/bmzg﹕ onViewReleased
12-15 14:41:28.275  19489-19489/com.baimi.wallet D/bmzg﹕ getViewHorizontalDragRange
12-15 14:41:28.276  19489-19489/com.baimi.wallet D/bmzg﹕ getViewVerticalDragRange
12-15 14:41:28.276  19489-19489/com.baimi.wallet D/bmzg﹕ onViewDragStateChanged
12-15 14:41:28.285  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.301  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.317  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.334  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.350  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.367  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.384  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.401  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.417  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.435  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.450  19489-19489/com.baimi.wallet D/bmzg﹕ onViewPositionChanged
12-15 14:41:28.468  19489-19489/com.baimi.wallet D/bmzg﹕ onViewDragStateChanged

这是一次从右边拖拽到左边的接口回调顺序，我的想法是，在第一个回调的方法内去改变view的背景，然后去刷新UI，想法貌似不错，我们试试吧。在getViewHorizontalDragRange方法内加入一下代码：

if (isChangeView && ViewDragHelper.STATE_DRAGGING == mDragger.getViewDragState()) {
dragView.setBackgroundResource(R.drawable.icon_cash_back_draging);
isChangeView = false;
invalidate();
}

我们的想法貌似要破产了，还是不行，第三猜想破产，那我们应该怎么办呢？

其实，view会跳回到初始化的位置，是因为view在设置layout的时候，使用了默认的位置，也就是初始化的位置，解决方案可参考：ViewDragHelper自定义view保存view的位置，希望本篇博客对各位博友有所帮助。

参考文献：Android ViewDragHelper完全解析 自定义ViewGroup神器