Android实现回弹效果
鸿鹄志远 人气:0在ios手机上经常看到页面上下滑动回弹效果,安卓中没有原生控件支持,这里自己就去自定义一个scrollview实现回弹效果
1. 新建MyScrollView并继承ScrollView,可以通过事件分发机制拦截并处理滑动事件
2. 重写事件分发拦截事件onInterceptTouchEvent方法,计算是否需要拦截事件
//拦截:实现父视图对子视图的拦截 //是否拦截成功,取决于方法的返回值。返回值true:拦截成功。反之,拦截失败 private int lastY;//上一次y轴方向操作的坐标位置 private Rect normal = new Rect();//用于记录临界状态的左、上、右、下 private boolean isFinishAnimation = true;//是否动画结束 private int lastX, downX, downY; @Override public boolean onInterceptTouchEvent(MotionEvent ev) { boolean isIntercept = false; int eventX = (int) ev.getX(); int eventY = (int) ev.getY(); switch (ev.getAction()) { case MotionEvent.ACTION_DOWN: lastX = downX = eventX; lastY = downY = eventY; break; case MotionEvent.ACTION_MOVE: //获取水平和垂直方向的移动距离 int absX = Math.abs(eventX - downX); int absY = Math.abs(eventY - downY); if(absY > absX && absY >= dp2px(10)){ isIntercept = true;//执行拦截 } lastX = eventX; lastY = eventY; break; } return isIntercept; }
3. 得到scrollview的子view,便于操作
//获取子视图 @Override protected void onFinishInflate() { super.onFinishInflate(); if (getChildCount() > 0) { childView = getChildAt(0); } }
4. 计算是否需要平移动画
private boolean isNeedMove() { int childMeasuredHeight = childView.getMeasuredHeight();//获取子视图的高度 int scrollViewMeasuredHeight = this.getMeasuredHeight();//获取布局的高度 Log.e("TAG", "childMeasuredHeight = " + childMeasuredHeight); Log.e("TAG", "scrollViewMeasuredHeight = " + scrollViewMeasuredHeight); int dy = childMeasuredHeight - scrollViewMeasuredHeight;//dy >= 0 int scrollY = this.getScrollY();//获取用户在y轴方向上的偏移量 (上 + 下 -) if (scrollY <= 0 || scrollY >= dy) { return true;//按照我们自定义的MyScrollView的方式处理 } //其他处在临界范围内的,返回false。即表示,仍按照ScrollView的方式处理 return false; }
5. 判断是否需要平移动画
//判断是否需要执行平移动画 private boolean isNeedAnimation() { return !normal.isEmpty(); }
6. 既然我们做了事件拦截,那么就要重写ontouchevent来执行响应事件
@Override public boolean onTouchEvent(MotionEvent ev) { if (childView == null || !isFinishAnimation) { return super.onTouchEvent(ev); } int eventY = (int) ev.getY();//获取当前的y轴坐标 switch (ev.getAction()) { case MotionEvent.ACTION_DOWN: lastY = eventY; break; case MotionEvent.ACTION_MOVE: int dy = eventY - lastY;//微小的移动量 if (isNeedMove()) { if (normal.isEmpty()) { //记录了childView的临界状态的左、上、右、下 normal.set(childView.getLeft(), childView.getTop(), childView.getRight(), childView.getBottom()); } //重新布局 childView.layout(childView.getLeft(), childView.getTop() + dy / 2, childView.getRight(), childView.getBottom() + dy / 2); } lastY = eventY;//重新赋值 break; case MotionEvent.ACTION_UP: if (isNeedAnimation()) { //使用平移动画 int translateY = childView.getBottom() - normal.bottom; TranslateAnimation translateAnimation = new TranslateAnimation(0, 0, 0, -translateY); translateAnimation.setDuration(200); // translateAnimation.setFillAfter(true);//停留在最终位置上 translateAnimation.setAnimationListener(new Animation.AnimationListener() { @Override public void onAnimationStart(Animation animation) { isFinishAnimation = false; } @Override public void onAnimationEnd(Animation animation) { isFinishAnimation = true; childView.clearAnimation();//清除动画 //重新布局 childView.layout(normal.left, normal.top, normal.right, normal.bottom); //清除normal的数据 normal.setEmpty(); } @Override public void onAnimationRepeat(Animation animation) { } }); //启动动画 childView.startAnimation(translateAnimation); } break; } return super.onTouchEvent(ev); }
这样整个view的核心部分已经完成了,把view嵌套到定义好了的scrollview就可以实现页面的滑动回弹效果了。
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