android自定义ViewPager水平滑动弹性效果
android ViewPager是一个经常要用到的组件，但android系统本身为我们提供的ViewPager是没有任何效果的，只能是一页一页的滑动，这样会让人感觉很死板，在看一些知名大公司的App时，看到了他们的ViewPager在滑动到最开始或者最后的时候是有一个弹性效果的，使用起来感觉非常的好，于是乎就是百度搜了一下，在StackOverflow中看到一篇文章就是讲如何实现这个效果的。
先看下效果图：滑动到最后一页时仍然可以拉动……
代码如下：
package com.example.myviewpager;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Camera;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.ViewConfigurationCompat;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Transformation;
import com.nineoldandroids.animation.Animator;
import com.nineoldandroids.animation.Animator.AnimatorListener;
import com.nineoldandroids.animation.ObjectAnimator;
public class BounceBackViewPager extends ViewPager
{
/**
* maximum z distance to translate child view
*/
final static int DEFAULT_OVERSCROLL_TRANSLATION = 500;
/**
* 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_bounce,
DEFAULT_OVERSCROLL_TRANSLATION);
mOverscrollAnimationDuration = a.getInt(R.styleable.BounceBackViewPager_overscroll_animation_duration_bounce,
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;
}
}
自定义属性如下：
<declare-styleable name="BounceBackViewPager">
<attr name="overscroll_translation_bounce" format="dimension" />
<!-- Duration of animation when user releases the over scroll. Default is 400 ms. -->
<attr name="overscroll_animation_duration_bounce" format="integer" />
</declare-styleable>
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