前言

拖動清除未讀訊息可以說在很多應用中都很常見，也被用戶廣泛接受，本文是一個可以供參考的Demo，希望能有幫助，

提示：以下是本篇文章正文內容，下面案例可供參考

最終效果圖及思路

實作關鍵：氣泡中間的兩條邊，分別是以ab，cd為資料點，G為控制點的貝塞爾曲線，

步驟：繪制圓背景以及文本；連接情況繪制貝塞爾曲線；另外端點繪制一個圓

關鍵代碼

1.定義，初始化等

狀態：靜止、連接、分離、消失
在onSizeChanged中初始化狀態，固定氣泡以及可動氣泡的圓心

代碼如下（示例）：

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);

    init(w, h);
}

private void init(int w, int h) {
    mBubbleState = BUBBLE_STATE_DEFAULT;

    //設定固定氣泡圓心初始坐標
    if (mBubFixedCenter == null) {
        mBubFixedCenter = new PointF(w / 2, h / 2);
    } else {
        mBubFixedCenter.set(w / 2, h / 2);
    }
    //設定可動氣泡圓心初始坐標
    if (mBubMovableCenter == null) {
        mBubMovableCenter = new PointF(w / 2, h / 2);
    } else {
        mBubMovableCenter.set(w / 2, h / 2);
    }
}

2.onDraw中繪制包括三樣繪制

第一樣：靜止，連接，分離狀態都需要繪制圓背景以及文本：

//靜止，連接，分離狀態都需要繪制圓背景以及文本
if (mBubbleState != BUBBLE_STATE_DISMISS) {
    canvas.drawCircle(mBubMovableCenter.x, mBubMovableCenter.y, mBubMovableRadius, mBubblePaint);
    mTextPaint.getTextBounds(mTextStr, 0, mTextStr.length(), mTextRect);
    canvas.drawText(mTextStr, mBubMovableCenter.x - mTextRect.width() / 2, mBubMovableCenter.y + mTextRect.height() / 2, mTextPaint);
}	

第二樣：連接狀態繪制貝塞爾曲線①，

if (mBubbleState == BUBBLE_STATE_CONNECT) {
    //繪制靜止的氣泡
    canvas.drawCircle(mBubFixedCenter.x, mBubFixedCenter.y, mBubFixedRadius, mBubblePaint);
    //計算控制點的坐標
    int iAnchorX = (int) ((mBubMovableCenter.x + mBubFixedCenter.x) / 2);
    int iAnchorY = (int) ((mBubMovableCenter.y + mBubFixedCenter.y) / 2);

    float sinTheta = (mBubMovableCenter.y - mBubFixedCenter.y) / mDist;
    float cosTheta = (mBubMovableCenter.x - mBubFixedCenter.x) / mDist;

    //D
    float iBubFixedStartX = mBubFixedCenter.x - mBubFixedRadius * sinTheta;
    float iBubFixedStartY = mBubFixedCenter.y + mBubFixedRadius * cosTheta;
    //C
    float iBubMovableEndX = mBubMovableCenter.x - mBubMovableRadius * sinTheta;
    float iBubMovableEndY = mBubMovableCenter.y + mBubMovableRadius * cosTheta;

    //A
    float iBubFixedEndX = mBubFixedCenter.x + mBubFixedRadius * sinTheta;
    float iBubFixedEndY = mBubFixedCenter.y - mBubFixedRadius * cosTheta;
    //B
    float iBubMovableStartX = mBubMovableCenter.x + mBubMovableRadius * sinTheta;
    float iBubMovableStartY = mBubMovableCenter.y - mBubMovableRadius * cosTheta;

    mBezierPath.reset();
    mBezierPath.moveTo(iBubFixedStartX, iBubFixedStartY);
    mBezierPath.quadTo(iAnchorX, iAnchorY, iBubMovableEndX, iBubMovableEndY);

    mBezierPath.lineTo(iBubMovableStartX, iBubMovableStartY);
    mBezierPath.quadTo(iAnchorX, iAnchorY, iBubFixedEndX, iBubFixedEndY);
    mBezierPath.close();
    canvas.drawPath(mBezierPath, mBubblePaint);
}

第三樣：消失狀態執行爆炸影片

// 認為是消失狀態，執行爆炸影片
if (mBubbleState == BUBBLE_STATE_DISMISS && mCurDrawableIndex < mBurstBitmapsArray.length) {
    mBurstRect.set(
            (int) (mBubMovableCenter.x - mBubMovableRadius),
            (int) (mBubMovableCenter.y - mBubMovableRadius),
            (int) (mBubMovableCenter.x + mBubMovableRadius),
            (int) (mBubMovableCenter.y + mBubMovableRadius));
    canvas.drawBitmap(mBurstBitmapsArray[mCurDrawableIndex], null, mBurstRect, mBubblePaint);
}

3.onTouchEvent中

按下：區分靜止狀態和連接狀態

case MotionEvent.ACTION_DOWN:
   if (mBubbleState != BUBBLE_STATE_DISMISS) {
        mDist = (float) Math.hypot(event.getX() - mBubFixedCenter.x, event.getY() - mBubFixedCenter.y);
        if (mDist < mBubbleRadius + MOVE_OFFSET) {
            //加上MOVE_OFFSET是為了方便拖拽
            mBubbleState = BUBBLE_STATE_CONNECT;
        } else {
            mBubbleState = BUBBLE_STATE_DEFAULT;
        }
    }
    break;

移動：判斷是否到了分離狀態

case MotionEvent.ACTION_MOVE:
    if (mBubbleState != BUBBLE_STATE_DEFAULT) {
        mDist = (float) Math.hypot(event.getX() - mBubFixedCenter.x, event.getY() - mBubFixedCenter.y);
        mBubMovableCenter.x = event.getX();
        mBubMovableCenter.y = event.getY();
        if (mBubbleState == BUBBLE_STATE_CONNECT) {
            if (mDist < mMaxDist - MOVE_OFFSET) {
                mBubFixedRadius = mBubbleRadius - mDist / 8;
            } else {
                mBubbleState = BUBBLE_STATE_APART;
            }
        }
        invalidate();
    }
    break;

彈起：判斷是否已經到了分離狀態，分離狀態爆炸，未分離反彈

case MotionEvent.ACTION_UP:
    if (mBubbleState == BUBBLE_STATE_CONNECT) {
        // 橡皮筋影片
        startBubbleRestAnim();
    } else if (mBubbleState == BUBBLE_STATE_APART) {
        if (mDist < 2 * mBubbleRadius){
            //反彈影片
            startBubbleRestAnim();
        }else{
            // 爆炸影片
            startBubbleBurstAnim();
        }
    }
    break;

4.反彈和爆炸影片

/**
 * 連接狀態下松開手指，執行類似橡皮筋影片
 */
private void startBubbleRestAnim() {
    ValueAnimator anim = ValueAnimator.ofObject(new PointFEvaluator(),
            new PointF(mBubMovableCenter.x, mBubMovableCenter.y),
            new PointF(mBubFixedCenter.x, mBubFixedCenter.y));
    anim.setDuration(200);
    anim.setInterpolator(new OvershootInterpolator(5f));
    anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            mBubMovableCenter = (PointF) animation.getAnimatedValue();
            invalidate();
        }
    });
    anim.addListener(new AnimatorListenerAdapter() {
        @Override
        public void onAnimationEnd(Animator animation) {
            super.onAnimationEnd(animation);
            mBubbleState = BUBBLE_STATE_DEFAULT;
        }
    });
    anim.start();
}

/**
  * 爆炸影片
  */
 private void startBubbleBurstAnim() {
     //將氣泡改成消失狀態
     mBubbleState = BUBBLE_STATE_DISMISS;
     ValueAnimator animator = ValueAnimator.ofInt(0, mBurstBitmapsArray.length);
     animator.setInterpolator(new LinearInterpolator());
     animator.setDuration(500);
     animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
         @Override
         public void onAnimationUpdate(ValueAnimator animation) {
             mCurDrawableIndex = (int) animation.getAnimatedValue();
             invalidate();
         }
     });
     animator.start();
 }

總結

注：①貝塞爾曲線參考博文

本文完，有需要參考的同學→文中Demo下載地址

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