android 自定义ListView仿IOS"阻尼"效果

    今天又在IOS上看到列表的"阻尼"效果，就是列表拉到表头或者表尾时，还能够继续往上或往下拉，松开手后，整个列表会弹回去，来看效果图：
   
  
   
    整个实现重点在overScrollBy这个方法上，当你滚动listview时会触发此事件，它会根据表头或表尾的坐标，及你所给的maxOverScrollY最大滚动纵坐标值来计算listview的表头或表尾的坐标。
  
    默认的ListView的overScrollBy方法中maxOverScrollY=0；因此你只能看到在表头或表尾有一条带颜色的线闪灯，听说，这是为了不IOS的专利....

    下面来看实现方式：

   activity_main.xml：

<com.example.tt.BaseListView
        android:id="@+id/mylistview"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
    </com.example.tt.BaseListView>

    MainActivity.java：

public class MainActivity extends Activity {

	private BaseListView listview;

	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		requestWindowFeature(Window.FEATURE_NO_TITLE);
		setContentView(R.layout.activity_main);
		listview = (BaseListView) findViewById(R.id.mylistview);
		ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_expandable_list_item_1, new String[] { "A", "A", "A", "A", "A", "A", "A", "A", "A"});
		listview.setAdapter(adapter);
	}

}

     这个是重点
     BaseListView.java

public class BaseListView extends ListView
{
	private static final int MAX_Y_OVERSCROLL_DISTANCE = 200;

	private Context mContext;
	private int mMaxYOverscrollDistance;

	public BaseListView(Context context)
	{
		super(context);
		mContext = context;
		initBounceListView();
	}

	public BaseListView(Context context, AttributeSet attrs)
	{
		super(context, attrs);
		mContext = context;
		initBounceListView();
	}

	public BaseListView(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)
	{
		return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, mMaxYOverscrollDistance, isTouchEvent);
	}
	
}

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