Android的ListView弹动效果

import android.content.Context;  
import android.util.AttributeSet;  
import android.util.DisplayMetrics;  
import android.widget.ListView;  
/** 
 * 弹性ListView。 
 * @author E 
 */  
public class FlexiListView extends ListView{  
    //初始可拉动Y轴方向距离  
    private static final int MAX_Y_OVERSCROLL_DISTANCE = 100;  
    //上下文环境  
    private Context mContext;  
    //实际可上下拉动Y轴上的距离  
    private int mMaxYOverscrollDistance;  
      
    public FlexiListView(Context context){  
        super(context);  
        mContext = context;  
        initBounceListView();  
    }  
      
    public FlexiListView(Context context, AttributeSet attrs) {  
        super(context, attrs);  
        mContext = context;  
        initBounceListView();  
    }  
      
    public FlexiListView(Context context, AttributeSet attrs, int defStyle) {  
        super(context, attrs, defStyle);  
        mContext = context;  
        initBounceListView();  
    }  
      
    private void initBounceListView(){  
        final DisplayMetrics metrics = mContext.getResources().getDisplayMetrics();  
            final float density = metrics.density;  
        mMaxYOverscrollDistance = (int) (density * MAX_Y_OVERSCROLL_DISTANCE);  
    }  
      
    @Override  
    protected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, int scrollRangeX,   
            int scrollRangeY, int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {   
        //实现的本质就是在这里动态改变了maxOverScrollY的值  
        return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, mMaxYOverscrollDistance, isTouchEvent);    
    }  
      
}