Android高仿QQ小红点功能

@Override
public boolean onTouchEvent(MotionEvent event) {
  //获得根View
  View rootView = getRootView();
  //获得触摸位置在全屏所在位置
  float mRawX = event.getRawX();
  float mRawY = event.getRawY();
  switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
      //请求父View不拦截
      getParent().requestDisallowInterceptTouchEvent(true);
      //获得当前View在屏幕上的位置
      int[] cLocation = new int[2];
      getLocationOnScreen(cLocation);
      if (rootView instanceof ViewGroup) {
        //初始化拖拽时显示的View
        dragView = new DragView(getContext());
        //设置固定圆的圆心坐标
        dragView.setStickyPoint(cLocation[0] + mWidth / 2, cLocation[1] + mHeight / 2, mRawX, mRawY);
        //获得缓存的bitmap，滑动时直接通过drawBitmap绘制出来
        setDrawingCacheEnabled(true);
        Bitmap bitmap = getDrawingCache();
        if (bitmap != null) {
          dragView.setCacheBitmap(bitmap);
          //将DragView添加到RootView中，这样就可以全屏滑动了
          ((ViewGroup) rootView).addView(dragView);
          setVisibility(INVISIBLE);
        }
      }
      break;
    case MotionEvent.ACTION_MOVE:
      //请求父View不拦截
      getParent().requestDisallowInterceptTouchEvent(true);
      if (dragView != null) {
        //更新DragView的位置
        dragView.setDragViewLocation(mRawX, mRawY);
      }
      break;
    case MotionEvent.ACTION_UP:
      getParent().requestDisallowInterceptTouchEvent(false);
      if (dragView != null) {
        //手抬起时来判断各种情况
        dragView.setDragUp();
      }
      break;
  }
  return true;
}

 private int mState;//当前红点的状态
 private static final int STATE_INIT = 0;//默认静止状态
 private static final int STATE_DRAG = 1;//拖拽状态
 private static final int STATE_MOVE = 2;//移动状态
 private static final int STATE_DISMISS = 3;//消失状态

/**
 * 设置固定圆的圆心和半径
 * @param stickyX 固定圆的X坐标
 * @param stickyY 固定圆的Y坐标
 */
 public void setStickyPoint(float stickyX, float stickyY, float touchX, float touchY) {
   //分别设置固定圆和拖拽圆的坐标
   stickyPointF.set(stickyX, stickyY);
   dragPointF.set(touchX, touchY);
   //通过两个圆点算出圆心距，也是拖拽的距离
   dragDistance = MathUtil.getTwoPointDistance(dragPointF, stickyPointF);
   if (dragDistance <= maxDistance) {
     //如果拖拽距离小于规定最大距离，则固定的圆应该越来越小，这样看着才符合实际
     stickRadius = (int) (defaultRadius - dragDistance / 10) < 10 ? 10 : (int) (defaultRadius - dragDistance / 10);
     mState = STATE_DRAG;
   } else {
     mState = STATE_INIT;
   }
 }

 /**
 * 设置拖拽的坐标位置
 *
 * @param touchX 拖拽时的X坐标
 * @param touchY 拖拽时的Y坐标
 */
 public void setDragViewLocation(float touchX, float touchY) {
   dragPointF.set(touchX, touchY);
   //随时更改圆心距
   dragDistance = MathUtil.getTwoPointDistance(dragPointF, stickyPointF);
   if (mState == STATE_DRAG) {
    if (isInsideRange()) {
       stickRadius = (int) (defaultRadius - dragDistance / 10) < 10 ? 10 : (int) (defaultRadius - dragDistance / 10);
     } else {
       mState = STATE_MOVE;
       if (onDragListener != null) {
         onDragListener.onMove();
       }
     }
   }
   invalidate();
 }

public void setDragUp() {
  if (mState == STATE_DRAG && isInsideRange()) {
    //拖拽状态且在范围之内
    startResetAnimator();
   } else if (mState == STATE_MOVE) {
     if (isInsideRange()) {
      //在范围之内 需要RESET
      startResetAnimator();
    } else {
      //在范围之外 消失动画
      mState = STATE_DISMISS;
      startExplodeAnim();
    }
  }
}

@Override
 protected void onDraw(Canvas canvas) {
   if (isInsideRange() && mState == STATE_DRAG) {
     mPaint.setColor(Color.RED);
     //绘制固定的小圆
     canvas.drawCircle(stickyPointF.x, stickyPointF.y, stickRadius, mPaint);
     //首先获得两圆心之间的斜率
     Float linK = MathUtil.getLineSlope(dragPointF, stickyPointF);
     //然后通过两个圆心和半径、斜率来获得外切线的切点
     PointF[] stickyPoints = MathUtil.getIntersectionPoints(stickyPointF, stickRadius, linK);
     dragRadius = (int) Math.min(mWidth, mHeight) / 2;
     PointF[] dragPoints = MathUtil.getIntersectionPoints(dragPointF, dragRadius, linK);
     mPaint.setColor(Color.RED);
     //二阶贝塞尔曲线的控制点取得两圆心的中点
     controlPoint = MathUtil.getMiddlePoint(dragPointF, stickyPointF);
     //绘制贝塞尔曲线
     mPath.reset();
     mPath.moveTo(stickyPoints[0].x, stickyPoints[0].y);
     mPath.quadTo(controlPoint.x, controlPoint.y, dragPoints[0].x, dragPoints[0].y);
     mPath.lineTo(dragPoints[1].x, dragPoints[1].y);
     mPath.quadTo(controlPoint.x, controlPoint.y, stickyPoints[1].x, stickyPoints[1].y);
     mPath.lineTo(stickyPoints[0].x, stickyPoints[0].y);
     canvas.drawPath(mPath, mPaint);
   }
   if (mCacheBitmap != null && mState != STATE_DISMISS) {
     //绘制缓存的Bitmap
     canvas.drawBitmap(mCacheBitmap, dragPointF.x - mWidth / 2,
            dragPointF.y - mHeight / 2, mPaint);
   }
   if (mState == STATE_DISMISS && explodeIndex < explode_res.length) {
     //绘制小红点消失时的爆炸动画
     canvas.drawBitmap(bitmaps[explodeIndex], dragPointF.x - mWidth / 2, dragPointF.y - mHeight / 2, mPaint);
   }
 }