android listview仿iphone弹簧特效

IOS常见视图有一个弹性回退的动画效果，Android 从2.3开始实现了下冲到底部和上冲到底部时颜色渐变动画效果。View类有两个很重要的方法scrollTo和scrollBy，允许移动视图的可见区域。这就是我们今天实现动画效果的理论基础，我们可以在android数据列表顶部往下拖动列表或底部拖动相应的移动数据列表，当停止拖动时再让它弹回去。下面是代码部分：

package com.linghu;  import android.content.Context; import android.util.AttributeSet; import android.view.MotionEvent; import android.widget.ListView; public class Pull_ListView extends ListView implements Runnable {     private float mLastDownY = 0f;     private int mDistance = 0;     private int mStep = 10;     private boolean mPositive = false;      public Pull_ListView (Context context, AttributeSet attrs) {           super(context, attrs);     }      public Pull_ListView (Context context, AttributeSet attrs, int defStyle) {           super(context, attrs, defStyle);     }      public Pull_ListView (Context context) {           super(context);     }      @Override     public boolean onTouchEvent(MotionEvent event) {          switch (event.getAction()) {               case MotionEvent.ACTION_DOWN:                    if (mLastDownY == 0f && mDistance == 0) {                          mLastDownY = event.getY();                    return true;               }               break;      case MotionEvent.ACTION_CANCEL:            break;    case MotionEvent.ACTION_UP:           if (mDistance != 0) {            mStep = 1;            mPositive = (mDistance >= 0);            this.post(this);            return true;         }         mLastDownY = 0f;         mDistance = 0;         break;      case MotionEvent.ACTION_MOVE:         if (mLastDownY != 0f) {               mDistance = (int) (mLastDownY - event.getY());               if ((mDistance < 0 && getFirstVisiblePosition() == 0 && getChildAt(0).getTop() == 0) || (mDistance > 0 && getLastVisiblePosition() == getCount() - 1)) {                    mDistance /= 2;                    scrollTo(0, mDistance);                    return true;                }         }         mDistance = 0;         break;         }         return super.onTouchEvent(event);     }      @Override     public void run() {           mDistance += mDistance > 0 ? -mStep : mStep;           scrollTo(0, mDistance);           if ((mPositive && mDistance <= 0) || (!mPositive && mDistance >= 0)) {                 scrollTo(0, 0);                 mDistance = 0;                 mLastDownY = 0f;                 return;            }           mStep += 1;           this.postDelayed(this, 10);      } } // end class

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