Android进阶篇自定义ScrollView反弹效果

public class autoScrollView extends ScrollView {  
    private View inner;  
    private float y;  
    private Rect normal = new Rect();  
      
    public autoScrollView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }

    public autoScrollView(Context context, AttributeSet attrs) {  
        super(context, attrs);  
    }  
    
    public autoScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub
    }

    
    @Override  
    protected void onFinishInflate() {  
        if (getChildCount() > 0) {  
            inner = getChildAt(0);  
        }  
    }  
    
    @Override  
    public boolean onTouchEvent(MotionEvent ev) {  
        if (inner == null) {  
            return super.onTouchEvent(ev);  
        } else {  
            commOnTouchEvent(ev);  
        }  
  
        return super.onTouchEvent(ev);  
    }  
  
    public void commOnTouchEvent(MotionEvent ev) {  
        int action = ev.getAction();  
        switch (action) {  
        case MotionEvent.ACTION_DOWN:  
            y = ev.getY();  
            break;  
        case MotionEvent.ACTION_UP:  
            if (isNeedAnimation()) {  
                animation();  
            }  
            break;  
        case MotionEvent.ACTION_MOVE:  
            final float preX = y;  
            float nowY = ev.getY();  
            int deltaY = (int) (preX - nowY);  
            // 滚动   
            scrollBy(0, deltaY); 
  
            y = nowY;  
            // 当滚动到最左或者最右时就不会再滚动，这时移动布局   
            if (isNeedMove()) {  
                if (normal.isEmpty()) {  
                    // 保存正常的布局位置   
                    normal.set(inner.getLeft(), inner.getTop(), inner.getRight(), inner.getBottom());  
                }  
                // 移动布局   
                inner.layout(inner.getLeft(), inner.getTop()-deltaY/2, inner.getRight(), inner.getBottom()-deltaY/2);
            }  
            break;  
  
        default:  
            break;  
        }  
    }  
  
    // 开启动画移动   
    public void animation() {  
        // 开启移动动画   
        TranslateAnimation ta = new TranslateAnimation(0, 0, inner.getTop(), normal.top);  
        ta.setDuration(200);  
        inner.startAnimation(ta);  
        // 设置回到正常的布局位置   
        inner.layout(normal.left, normal.top, normal.right, normal.bottom);  
        normal.setEmpty();  
    }  
    
    // 是否需要开启动画   
    public boolean isNeedAnimation() {  
        return !normal.isEmpty();  
    }  
    
    // 是否需要移动布局   
    public boolean isNeedMove() {  
        int offset = inner.getMeasuredHeight() - getHeight();  
        int scrollY = getScrollY();  
        if (scrollY == 0 || scrollY == offset) {  
            return true;  
        }  
        return false;  
    }  
}