android之luncher滑动效果

Java代码：

import android.content.Context;

import android.util.Log;
import android.content.res.TypedArray;

import android.util.AttributeSet;

import android.view.MotionEvent;
import android.view.VelocityTracker;

import android.view.View;
import android.view.ViewGroup;

import android.view.ViewConfiguration;

import android.widget.Scroller;

public class DragableSpace extends ViewGroup {

private Scroller mScroller;

private VelocityTracker mVelocityTracker;

private int mScrollX = 0;

private int mCurrentScreen = 0;

private float mLastMotionX;

private static final String LOG_TAG = "DragableSpace";

private static final int SNAP_VELOCITY = 1000;

private final static int TOUCH_STATE_REST = 0;

private final static int TOUCH_STATE_SCROLLING = 1;

private int mTouchState = TOUCH_STATE_REST;

private int mTouchSlop = 0;

public DragableSpace(Context context) {

super(context);

mScroller = new Scroller(context);

mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();

this.setLayoutParams(new ViewGroup.LayoutParams(

ViewGroup.LayoutParams.WRAP_CONTENT,

ViewGroup.LayoutParams.FILL_PARENT));

}

public DragableSpace(Context context, AttributeSet attrs) {

super(context, attrs);

mScroller = new Scroller(context);

mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();

this.setLayoutParams(new ViewGroup.LayoutParams(

ViewGroup.LayoutParams.WRAP_CONTENT ,

ViewGroup.LayoutParams.FILL_PARENT));

TypedArray a=getContext().obtainStyledAttributes(attrs,R.styleable.DragableSpace);

mCurrentScreen = a.getInteger(R.styleable.DragableSpace_default_screen, 0);

}

@Override

public boolean onInterceptTouchEvent(MotionEvent ev) {

final int action = ev.getAction();

if ((action == MotionEvent.ACTION_MOVE)

&& (mTouchState != TOUCH_STATE_REST)) {

return true;

}

final float x = ev.getX();

switch (action) {

case MotionEvent.ACTION_MOVE:

final int xDiff = (int) Math.abs(x - mLastMotionX);

boolean xMoved = xDiff > mTouchSlop;

if (xMoved) {

// Scroll if the user moved far enough along the X axis

mTouchState = TOUCH_STATE_SCROLLING;

}

break;

case MotionEvent.ACTION_DOWN:

// Remember location of down touch

mLastMotionX = x;

mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;

break;

case MotionEvent.ACTION_CANCEL:

case MotionEvent.ACTION_UP:

// Release the drag

mTouchState = TOUCH_STATE_REST;

break;

}

return mTouchState != TOUCH_STATE_REST;

}

@Override

public boolean onTouchEvent(MotionEvent event) {

if (mVelocityTracker == null) {

mVelocityTracker = VelocityTracker.obtain();

}
mVelocityTracker.addMovement(event);

final int action = event.getAction();

final float x = event.getX();

switch (action) {

case MotionEvent.ACTION_DOWN:

Log.i(LOG_TAG, "event : down");

if (!mScroller.isFinished()) {

mScroller.abortAnimation();

}

// Remember where the motion event started

mLastMotionX = x;

break;

case MotionEvent.ACTION_MOVE:

// Log.i(LOG_TAG,"event : move");

// if (mTouchState == TOUCH_STATE_SCROLLING) {

// Scroll to follow the motion event

final int deltaX = (int) (mLastMotionX - x);

mLastMotionX = x;

//Log.i(LOG_TAG, "event : move, deltaX " + deltaX + ", mScrollX " + mScrollX);

if (deltaX < 0) {

if (mScrollX > 0) {

scrollBy(Math.max(-mScrollX, deltaX), 0);

}

} else if (deltaX > 0) {

final int availableToScroll = getChildAt(getChildCount() - 1)

.getRight()

- mScrollX - getWidth();

if (availableToScroll > 0) {

scrollBy(Math.min(availableToScroll, deltaX), 0);

}

}

// }

break;

case MotionEvent.ACTION_UP:

Log.i(LOG_TAG, "event : up");

// if (mTouchState == TOUCH_STATE_SCROLLING) {

final VelocityTracker velocityTracker = mVelocityTracker;

velocityTracker.computeCurrentVelocity(1000);

int velocityX = (int) velocityTracker.getXVelocity();

if (velocityX > SNAP_VELOCITY && mCurrentScreen > 0) {

// Fling hard enough to move left

snapToScreen(mCurrentScreen - 1);

} else if (velocityX < -SNAP_VELOCITY

&& mCurrentScreen < getChildCount() - 1) {

// Fling hard enough to move right

snapToScreen(mCurrentScreen + 1);

} else {

snapToDestination();

}

if (mVelocityTracker != null) {

mVelocityTracker.recycle();

mVelocityTracker = null;

}

// }

mTouchState = TOUCH_STATE_REST;

break;

case MotionEvent.ACTION_CANCEL:

Log.i(LOG_TAG, "event : cancel");

mTouchState = TOUCH_STATE_REST;

}
mScrollX = this.getScrollX();

return true;

}

private void snapToDestination() {

final int screenWidth = getWidth();

final int whichScreen = (mScrollX + (screenWidth / 2)) / screenWidth;

Log.i(LOG_TAG, "from des");

snapToScreen(whichScreen);

}

public void snapToScreen(int whichScreen) {

Log.i(LOG_TAG, "snap To Screen " + whichScreen);

mCurrentScreen = whichScreen;

final int newX = whichScreen * getWidth();

final int delta = newX - mScrollX;

mScroller.startScroll(mScrollX, 0, delta, 0, Math.abs(delta) * 2);

invalidate();

}

public void setToScreen(int whichScreen) {

Log.i(LOG_TAG, "set To Screen " + whichScreen);

mCurrentScreen = whichScreen;

final int newX = whichScreen * getWidth();

mScroller.startScroll(newX, 0, 0, 0, 10);

invalidate();

}

@Override

protected void onLayout(boolean changed, int l, int t, int r, int b) {

int childLeft = 0;

final int count = getChildCount();

for (int i = 0; i < count; i++) {

final View child = getChildAt(i);

if (child.getVisibility() != View.GONE) {

final int childWidth = child.getMeasuredWidth();

child.layout(childLeft, 0, childLeft + childWidth, child

.getMeasuredHeight());

childLeft += childWidth;

}

}

}

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

super.onMeasure(widthMeasureSpec, heightMeasureSpec);

final int width = MeasureSpec.getSize(widthMeasureSpec);

final int widthMode = MeasureSpec.getMode(widthMeasureSpec);

if (widthMode != MeasureSpec.EXACTLY) {

throw new IllegalStateException("error mode.");

}

final int heightMode = MeasureSpec.getMode(heightMeasureSpec);

if (heightMode != MeasureSpec.EXACTLY) {

throw new IllegalStateException("error mode.");

}

// The children are given the same width and height as the workspace

final int count = getChildCount();

for (int i = 0; i < count; i++) {

getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);

}
Log.i(LOG_TAG, "moving to screen "+mCurrentScreen);

scrollTo(mCurrentScreen * width, 0);

}

@Override

public void computeScroll() {

if (mScroller.computeScrollOffset()) {

mScrollX = mScroller.getCurrX();

scrollTo(mScrollX, 0);

postInvalidate();

}
}
}

Java代码：

<?xml version="1.0" encoding="utf-8"?>

<com.matthieu.launcher.DragableSpace xmlns:app="http://schemas.android.com/apk/res/com.matthieu.launcher"

xmlns:android="http://schemas.android.com/apk/res/android"

android:id="@+id/space"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

app:default_screen="1"

>

<include android:id="@+id/left" layout="@layout/left_screen" />

<include android:id="@+id/center" layout="@layout/initial_screen" />

<include android:id="@+id/right" layout="@layout/right_screen" />

</com.matthieu.launcher.DragableSpace>

values/attrs.xml

<?xml version="1.0" encoding="utf-8"?> <resources>     <declare-styleable name="DragableSpace">         <attr name="default_screen" format="integer"/>     </declare-styleable> </resources>

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