Android编程ViewPager回弹效果实例分析

package com.freesonfish.viewpager_2; import android.content.Context; import android.graphics.Rect; import android.support.v4.view.ViewPager; import android.util.AttributeSet; import android.view.KeyEvent; import android.view.MotionEvent; import android.view.animation.TranslateAnimation; public class MyViewPager extends ViewPager {   private Rect mRect = new Rect();//用来记录初始位置   private int pagerCount = 3;   private int currentItem = 0;   private boolean handleDefault = true;   private float preX = 0f;   private static final float RATIO = 0.5f;//摩擦系数   private static final float SCROLL_WIDTH = 30f;   public MyViewPager(Context context) {     super(context);   }   public MyViewPager(Context context, AttributeSet attrs) {     super(context, attrs);   }   //设置总共有多少页,请记得调用它   public void setpagerCount(int pagerCount) {     this.pagerCount = pagerCount;   }   //这是当前是第几页，请在onPageSelect方法中调用它。   public void setCurrentIndex(int currentItem) {     this.currentItem = currentItem;   }   @Override   public boolean dispatchKeyEvent(KeyEvent event) {     return super.dispatchKeyEvent(event);   }   @Override   public boolean onInterceptTouchEvent(MotionEvent arg0) {     if (arg0.getAction() == MotionEvent.ACTION_DOWN) {       preX = arg0.getX();//记录起点     }     return super.onInterceptTouchEvent(arg0);   }   @Override   public boolean onTouchEvent(MotionEvent arg0) {     switch (arg0.getAction()) {     case MotionEvent.ACTION_UP:       onTouchActionUp();       break;     case MotionEvent.ACTION_MOVE:       //当时滑到第一项或者是最后一项的时候。       if ((currentItem == 0 || currentItem == pagerCount - 1)) {         float nowX = arg0.getX();         float offset = nowX - preX;         preX = nowX;         if (currentItem == 0) {           if (offset > SCROLL_WIDTH) {//手指滑动的距离大于设定值             whetherConditionIsRight(offset);           } else if (!handleDefault) {//这种情况是已经出现缓冲区域了，手指慢慢恢复的情况             if (getLeft() + (int) (offset * RATIO) >= mRect.left) {              layout(getLeft() + (int) (offset * RATIO), getTop(), getRight() + (int) (offset * RATIO), getBottom());             }           }         } else {           if (offset < -SCROLL_WIDTH) {             whetherConditionIsRight(offset);           } else if (!handleDefault) {             if (getRight() + (int) (offset * RATIO) <= mRect.right) {               layout(getLeft() + (int) (offset * RATIO), getTop(), getRight() + (int) (offset * RATIO), getBottom());             }           }         }       } else {         handleDefault = true;       }       if (!handleDefault) {         return true;       }       break;     default:       break;     }     return super.onTouchEvent(arg0);   }   private void whetherConditionIsRight(float offset) {     if (mRect.isEmpty()) {       mRect.set(getLeft(), getTop(), getRight(), getBottom());     }     handleDefault = false;     layout(getLeft() + (int) (offset * RATIO), getTop(), getRight() + (int) (offset * RATIO), getBottom());   }   private void onTouchActionUp() {     if (!mRect.isEmpty()) {       recoveryPosition();     }   }   private void recoveryPosition() {     TranslateAnimation ta = null;     ta = new TranslateAnimation(getLeft(), mRect.left, 0, 0);     ta.setDuration(300);     startAnimation(ta);     layout(mRect.left, mRect.top, mRect.right, mRect.bottom);     mRect.setEmpty();     handleDefault = true;   } }