android viewpager 弹性效果的实现,首页往左拉弹回,尾页往右拉弹回

这个实现,我今天找了蛮久,最后决定用的方法是这个:

http://stackoverflow.com/questions/13759862/android-viewpager-how-to-achieve-the-bound-effect

直接按照上面的方法用这个就ok了,我实验了一下效果还非常不错.网上所说的多加两个空白页的方法纯属娱乐感觉.

BounceBackViewPager

直接在这里贴出吧

public class BounceBackViewPagerextends ViewPager {

/**
* maximum z distance to translate child view
*/
final static int DEFAULT_OVERSCROLL_TRANSLATION = 150;

/**
* duration of overscroll animation in ms
*/
final private static int DEFAULT_OVERSCROLL_ANIMATION_DURATION = 400;

@SuppressWarnings("unused")
private final static String DEBUG_TAG = ViewPager.class.getSimpleName();
private final static int INVALID_POINTER_ID = -1;

/**
*
* @author renard, extended by Piotr Zawadzki
*
*/
private class OverscrollEffect {
private float mOverscroll;
private Animator mAnimator;

/**
* @param deltaDistance [0..1] 0->no overscroll, 1>full overscroll
*/
public void setPull(final float deltaDistance) {
mOverscroll = deltaDistance;
invalidateVisibleChilds(mLastPosition);
}

/**
* called when finger is released. starts to animate back to default position
*/
private void onRelease() {
if (mAnimator != null && mAnimator.isRunning()) {
mAnimator.addListener(new AnimatorListener() {

@Override
public void onAnimationStart(Animator animation) {
}

@Override
public void onAnimationRepeat(Animator animation) {
}

@Override
public void onAnimationEnd(Animator animation) {
startAnimation(0);
}

@Override
public void onAnimationCancel(Animator animation) {
}
});
mAnimator.cancel();
} else {
startAnimation(0);
}
}

private void startAnimation(final float target) {
mAnimator = ObjectAnimator.ofFloat(this, "pull", mOverscroll, target);
mAnimator.setInterpolator(new DecelerateInterpolator());
final float scale = Math.abs(target - mOverscroll);
mAnimator.setDuration((long) (mOverscrollAnimationDuration * scale));
mAnimator.start();
}

private boolean isOverscrolling() {
if (mScrollPosition == 0 && mOverscroll < 0) {
return true;
}
final boolean isLast = (getAdapter().getCount() - 1) == mScrollPosition;
if (isLast && mOverscroll > 0) {
return true;
}
return false;
}

}

final private OverscrollEffect mOverscrollEffect = new OverscrollEffect();
final private Camera mCamera = new Camera();

private OnPageChangeListener mScrollListener;
private float mLastMotionX;
private int mActivePointerId;
private int mScrollPosition;
private float mScrollPositionOffset;
final private int mTouchSlop;

private float mOverscrollTranslation;
private int mOverscrollAnimationDuration;

public BounceBackViewPager(Context context, AttributeSet attrs) {
super(context, attrs);
setStaticTransformationsEnabled(true);
final ViewConfiguration configuration = ViewConfiguration.get(context);
mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration);
super.setOnPageChangeListener(new MyOnPageChangeListener());
init(attrs);
}

private void init(AttributeSet attrs) {
TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.BounceBackViewPager);
mOverscrollTranslation = a.getDimension(R.styleable.BounceBackViewPager_overscroll_translation, DEFAULT_OVERSCROLL_TRANSLATION);
mOverscrollAnimationDuration = a.getInt(R.styleable.BounceBackViewPager_overscroll_animation_duration, DEFAULT_OVERSCROLL_ANIMATION_DURATION);
a.recycle();
}

public int getOverscrollAnimationDuration() {
return mOverscrollAnimationDuration;
}

public void setOverscrollAnimationDuration(int mOverscrollAnimationDuration) {
this.mOverscrollAnimationDuration = mOverscrollAnimationDuration;
}

public float getOverscrollTranslation() {
return mOverscrollTranslation;
}

public void setOverscrollTranslation(int mOverscrollTranslation) {
this.mOverscrollTranslation = mOverscrollTranslation;
}

@Override
public void setOnPageChangeListener(OnPageChangeListener listener) {
mScrollListener = listener;
};

private void invalidateVisibleChilds(final int position) {
for (int i = 0; i < getChildCount(); i++) {
getChildAt(i).invalidate();

}
//this.invalidate();
// final View child = getChildAt(position);
// final View previous = getChildAt(position - 1);
// final View next = getChildAt(position + 1);
// if (child != null) {
// child.invalidate();
// }
// if (previous != null) {
// previous.invalidate();
// }
// if (next != null) {
// next.invalidate();
// }
}

private int mLastPosition = 0;

private class MyOnPageChangeListener implements OnPageChangeListener {

@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
if (mScrollListener != null) {
mScrollListener.onPageScrolled(position, positionOffset, positionOffsetPixels);
}
mScrollPosition = position;
mScrollPositionOffset = positionOffset;
mLastPosition = position;
invalidateVisibleChilds(position);
}

@Override
public void onPageSelected(int position) {

if (mScrollListener != null) {
mScrollListener.onPageSelected(position);
}
}

@Override
public void onPageScrollStateChanged(final int state) {

if (mScrollListener != null) {
mScrollListener.onPageScrollStateChanged(state);
}
if (state == SCROLL_STATE_IDLE) {
mScrollPositionOffset = 0;
}
}
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
try {
final int action = ev.getAction() & MotionEventCompat.ACTION_MASK;
switch (action) {
case MotionEvent.ACTION_DOWN: {
mLastMotionX = ev.getX();
mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
break;
}
case MotionEventCompat.ACTION_POINTER_DOWN: {
final int index = MotionEventCompat.getActionIndex(ev);
final float x = MotionEventCompat.getX(ev, index);
mLastMotionX = x;
mActivePointerId = MotionEventCompat.getPointerId(ev, index);
break;
}
}
return super.onInterceptTouchEvent(ev);
} catch (IllegalArgumentException e) {
e.printStackTrace();
return false;
} catch (ArrayIndexOutOfBoundsException e) {
e.printStackTrace();
return false;
}
}

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
try {
return super.dispatchTouchEvent(ev);
} catch (IllegalArgumentException e) {
e.printStackTrace();
return false;
} catch (ArrayIndexOutOfBoundsException e) {
e.printStackTrace();
return false;
}
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
boolean callSuper = false;

final int action = ev.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN: {
callSuper = true;
mLastMotionX = ev.getX();
mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
break;
}
case MotionEventCompat.ACTION_POINTER_DOWN: {
callSuper = true;
final int index = MotionEventCompat.getActionIndex(ev);
final float x = MotionEventCompat.getX(ev, index);
mLastMotionX = x;
mActivePointerId = MotionEventCompat.getPointerId(ev, index);
break;
}
case MotionEvent.ACTION_MOVE: {
if (mActivePointerId != INVALID_POINTER_ID) {
// Scroll to follow the motion event
final int activePointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
final float x = MotionEventCompat.getX(ev, activePointerIndex);
final float deltaX = mLastMotionX - x;
final float oldScrollX = getScrollX();
final int width = getWidth();
final int widthWithMargin = width + getPageMargin();
final int lastItemIndex = getAdapter().getCount() - 1;
final int currentItemIndex = getCurrentItem();
final float leftBound = Math.max(0, (currentItemIndex - 1) * widthWithMargin);
final float rightBound = Math.min(currentItemIndex + 1, lastItemIndex) * widthWithMargin;
final float scrollX = oldScrollX + deltaX;
if (mScrollPositionOffset == 0) {
if (scrollX < leftBound) {
if (leftBound == 0) {
final float over = deltaX + mTouchSlop;
mOverscrollEffect.setPull(over / width);
}
} else if (scrollX > rightBound) {
if (rightBound == lastItemIndex * widthWithMargin) {
final float over = scrollX - rightBound - mTouchSlop;
mOverscrollEffect.setPull(over / width);
}
}
} else {
mLastMotionX = x;
}
} else {
mOverscrollEffect.onRelease();
}
break;
}
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL: {
callSuper = true;
mActivePointerId = INVALID_POINTER_ID;
mOverscrollEffect.onRelease();
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex);
if (pointerId == mActivePointerId) {
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly.
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastMotionX = ev.getX(newPointerIndex);
mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex);
callSuper = true;
}
break;
}
}

if (mOverscrollEffect.isOverscrolling() && !callSuper) {
return true;
} else {
return super.onTouchEvent(ev);
}
}

@Override
protected boolean getChildStaticTransformation(View child, Transformation t) {
if (child.getWidth() == 0) {
return false;
}
final int position = child.getLeft() / child.getWidth();
final boolean isFirstOrLast = position == 0 || (position == getAdapter().getCount() - 1);
if (mOverscrollEffect.isOverscrolling() && isFirstOrLast) {
final float dx = getWidth() / 2;
final int dy = getHeight() / 2;
t.getMatrix().reset();
final float translateX =(float) mOverscrollTranslation * (mOverscrollEffect.mOverscroll > 0 ? Math.min(mOverscrollEffect.mOverscroll, 1) : Math.max(mOverscrollEffect.mOverscroll, -1));
mCamera.save();
mCamera.translate(-translateX, 0, 0);
mCamera.getMatrix(t.getMatrix());
mCamera.restore();
t.getMatrix().preTranslate(-dx, -dy);
t.getMatrix().postTranslate(dx, dy);

if (getChildCount() == 1) {
this.invalidate();
} else {
child.invalidate();
}
return true;
}
return false;
}

and add a resources file somewhere in the values folder:

<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="BounceBackViewPager">
<!--
determines the maximum amount of translation along the z-axis during the overscroll.
Default is 150.
-->
<attr name="overscroll_translation" format="dimension" />

<!-- Duration of animation when user releases the over scroll. Default is 400 ms. -->
<attr name="overscroll_animation_duration" format="integer" />
</declare-styleable>