【转】Android自定义控件（二）——有弹性的ScrollView

原文地址：http://blog.csdn.net/a105865708/article/details/17784041

实现了当手指滑动到ScrollView的顶部、底部时，

可以继续的向上、向下拉伸。当释放手指的时候，向上、下弹回。

效果如图所示：

主要代码：

    public class ElasticScrollView extends ScrollView {  
        private View inner;  
        private float y;  
        private Rect normal = new Rect();  
        private boolean animationFinish = true;  
      
        public ElasticScrollView(Context context) {  
            super(context);  
        }  
      
        public ElasticScrollView(Context context, AttributeSet attrs) {  
            super(context, attrs);  
        }  
      
        @Override  
        protected void onFinishInflate() {  
            if (getChildCount() > 0) {  
                inner = getChildAt(0);  
            }  
        }  
          
        @Override  
        public boolean onInterceptTouchEvent(MotionEvent ev) {  
            return super.onInterceptTouchEvent(ev);  
        }  
      
        @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) {  
            if (animationFinish) {  
                int action = ev.getAction();  
                switch (action) {  
                case MotionEvent.ACTION_DOWN:  
    //              System.out.println("ACTION_DOWN");  
                    y = ev.getY();  
                    super.onTouchEvent(ev);  
                    break;  
                case MotionEvent.ACTION_UP:  
    //              System.out.println("ACTION_UP");  
                    y = 0;  
                    if (isNeedAnimation()) {  
                        animation();  
                    }  
                    super.onTouchEvent(ev);  
                    break;  
                case MotionEvent.ACTION_MOVE:  
    //              System.out.println("ACTION_MOVE");  
                    final float preY = y == 0 ? ev.getY() : y;  
                    float nowY = ev.getY();  
                    int deltaY = (int) (preY - nowY);  
                    // 滚动  
    //              scrollBy(0, deltaY);  
      
                    y = nowY;  
                    // 当滚动到最上或者最下时就不会再滚动，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);  
                    } else {  
                        super.onTouchEvent(ev);  
                    }  
                    break;  
                default:  
                    break;  
                }  
            }  
        }  
      
        // 开启动画移动  
      
        public void animation() {  
            // 开启移动动画  
            TranslateAnimation ta = new TranslateAnimation(0, 0, 0, normal.top - inner.getTop());  
            ta.setDuration(200);  
            ta.setAnimationListener(new AnimationListener() {  
                @Override  
                public void onAnimationStart(Animation animation) {  
                    animationFinish = false;  
      
                }  
      
                @Override  
                public void onAnimationRepeat(Animation animation) {  
      
                }  
      
                @Override  
                public void onAnimationEnd(Animation animation) {  
                    inner.clearAnimation();  
                    // 设置回到正常的布局位置  
                    inner.layout(normal.left, normal.top, normal.right, normal.bottom);  
                    normal.setEmpty();  
                    animationFinish = true;  
                }  
            });  
            inner.startAnimation(ta);  
        }  
      
        // 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;  
        }  
      
    }