模仿QQ拖動清除消息提示

原文地址：http://blog.csdn.net/yebo0505/article/details/42779441
首先感謝這兩篇文章提供的思路和代碼

http://blog.csdn.net/chenupt/article/details/41478303

http://blog.csdn.net/singwhatiwanna/article/details/42614953

實現原理：
點擊屏幕，遍歷所有的view,匹配點擊的屏幕座標，是否在某個紅點提示的view範圍內，是的話，計算紅點提示的view,在自定義的佈局上對應的座標位置，計算出來的這個座標，當做其中的一個圓的圓心，在拖動的過程中，得到的另外的座標，當做是另外一個圓的圓心，在拖動的過程中，半徑變化，但兩個圓始終保持半徑一樣，利用貝塞爾曲線，畫出拖動的效果。
重要的代碼，都有註釋，代碼也比較少，代碼如下：

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/**   * @Title: DragTipsLayout.java * @Package com.eeb.dragredview * @Description: TODO(模仿QQ拖動消息提示) * @author luquan [email protected]   * @date 2015-1-4 上午11:57:48 * @version V1.0   */ package com.eeb.dragtipslayout;   import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.Path; import android.graphics.Rect; import android.graphics.RectF; import android.util.AttributeSet; import android.view.MotionEvent; import android.view.View; import android.view.ViewGroup; import android.widget.LinearLayout;   public class DragTipsLayout extends LinearLayout {     // 默認定點圓半徑     public static final float DEFAULT_RADIUS = 10;     private int[] mLocationInScreen = new int[2];       private Paint paint;     private Path path;     private boolean dragging;     // 手勢滑動是的動態座標     float touchX = 0;     float touchY = 0;       // 錨點座標，兩個圓圓心(手勢滑動座標和要拖動的bageview的中心)的中間點     float anchorX = 0;     float anchorY = 0;       // 定點圓半徑     float radius = DEFAULT_RADIUS;       // 要拖動的View的中心座標     private float mCenterX;     private float mCenterY;     private View targetView;       public DragTipsLayout(Context context) {         super(context);         init();     }       public DragTipsLayout(Context context, AttributeSet attrs) {         super(context, attrs);         init();     }       @Override     protected void onLayout(boolean changed, int l, int t, int r, int b) {         super.onLayout(changed, l, t, r, b);         this.getLocationOnScreen(mLocationInScreen);//DragTisLayout 在屏幕上的位置     }       @Override     protected void dispatchDraw(Canvas canvas) {         // TODO Auto-generated method stub         super.dispatchDraw(canvas);         if (dragging) {             // 畫拖動的效果，這裏計算的是在拖動的過程中，半徑變化，但兩個圓始終保持半徑一樣，如果半徑一大一小不同，需要另外計算             float distance = (float) Math.sqrt(Math.pow(touchY - mCenterY, 2)                     + Math.pow(touchX - mCenterX, 2));             radius = -distance / 20 + DEFAULT_RADIUS;             paint.setColor(Color.RED);             if (radius > 5) {                 float offsetX = (float) (radius * Math.sin(Math                         .atan((touchY - mCenterY) / (touchX - mCenterX))));                 float offsetY = (float) (radius * Math.cos(Math                         .atan((touchY - mCenterY) / (touchX - mCenterX))));                   float x1 = mCenterX - offsetX;                 float y1 = mCenterY + offsetY;                   float x2 = touchX - offsetX;                 float y2 = touchY + offsetY;                   float x3 = touchX + offsetX;                 float y3 = touchY - offsetY;                   float x4 = mCenterX + offsetX;                 float y4 = mCenterY - offsetY;                   path.reset();                 path.moveTo(x1, y1);                 path.quadTo(anchorX, anchorY, x2, y2);                 path.lineTo(x3, y3);                 path.quadTo(anchorX, anchorY, x4, y4);                 path.lineTo(x1, y1);                   canvas.drawCircle(mCenterX, mCenterY, radius, paint);                 canvas.drawPath(path, paint);             }                          if (targetView != null) {                 //計算字體所佔的位置大小，獲取拖動的badge大小，以確定在拖動過程中，字體居中，畫出拖動的view跟badgeview一樣                 String num = ((BadgeView) targetView).getText().toString();                 Rect rect = new Rect();                 paint.getTextBounds(num, 0, num.length(), rect);                 RectF rectF = new RectF(touchX-targetView.getWidth()/2,touchY-targetView.getHeight()/2,touchX+targetView.getWidth()/2,touchY+targetView.getHeight()/2);                 canvas.drawOval(rectF, paint);                 paint.setColor(Color.WHITE);                 canvas.drawText(num,touchX-rect.centerX(), touchY-rect.centerY(), paint);             }         }     }       private void init() {         setWillNotDraw(false);         path = new Path();         paint = new Paint();         paint.setAntiAlias(true);         paint.setStyle(Paint.Style.FILL_AND_STROKE);         paint.setStrokeWidth(1);         paint.setColor(Color.RED);     }       @Override     public boolean dispatchTouchEvent(MotionEvent event) {         switch (event.getAction()) {         case MotionEvent.ACTION_DOWN:             findTouchTarget(this, event.getRawX(), event.getRawY());             touchX = event.getX();             touchY = event.getY();             anchorX = touchX;             anchorY = touchY;             break;         case MotionEvent.ACTION_MOVE:             touchX = event.getX();             touchY = event.getY();             anchorX = (mCenterX + touchX) / 2;             anchorY = (mCenterY + touchY) / 2;             break;         case MotionEvent.ACTION_UP:             if (radius > 5 && targetView != null)                 targetView.setVisibility(View.VISIBLE);             dragging = false;             break;         }         invalidate();         //如果沒有拖動， 事件分發不做處理，正常使用點擊，長按事件，如果return true,可以理解爲事件不傳遞到子類，各個子view的點擊，滑動無效         if(dragging)             return true;         else             return super.dispatchTouchEvent(event);                  }       //遍歷DragTipsLayout下所有的view     private void findTouchTarget(ViewGroup viewGrop, float x, float y) {         for (int i = 0; i < viewGrop.getChildCount(); i++) {             View temp = viewGrop.getChildAt(i);             if (temp instanceof ViewGroup) {                 ViewGroup tempViewGrop = (ViewGroup) temp;                 findTouchTarget(tempViewGrop, x, y);//遞歸查找             } else if (temp instanceof BadgeView                     &&isTouchBadgeView(temp, x, y)){//判斷是否是BadgeView並且點擊屏幕的座標在BadgeView的區域範圍內                     dragging = true;             }         }     }       private boolean isTouchBadgeView(View view, float x, float y) {                  int[] location = new int[2];         view.getLocationOnScreen(location);         int left = location[0];         int top = location[1];         int right = left + view.getMeasuredWidth();         int bottom = top + view.getMeasuredHeight();         if (view.getVisibility() == View.VISIBLE && y >= top && y <= bottom                 && x >= left && x <= right) {             //依據遍歷找到的BadgeView,計算對應在DragTipsLayout上的座標點             mCenterX = (left + right) / 2 - - mLocationInScreen[0];             mCenterY = (top+bottom)/2 - mLocationInScreen[1];             targetView = view;                          view.setVisibility(View.INVISIBLE);             return true;         }         return false;     }   }