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，还可以继续往上或往下拉，松开手后，整个列表会弹回去，来看效果图：
   
   <IMG style="CURSOR: pointer" alt="android 自定义ListView仿IOS" src="https://simg.open-open.com/show/cc1d7e45ae70929f7fe6f41f6384d792.png" width=480 height=800 阻尼?效果?="">
   
    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；所以你只能看到在表头或表尾有一条带颜色的线
闪灯，据说，这是为了避免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);   }    }

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);   }     }