【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;
         }  

     }