<p>QQ的未读消息，算是一个比较好玩的效果，趁着最近时间比较多，参考了网上的一些资料之后，本次实现一个仿照QQ未读消息的拖拽小红点，最终完成效果如下：</p>    <p style="text-align: center;"><img src="https://simg.open-open.com/show/62cf2d2268ea545be22f939dc3438c5e.gif"></p>    <p>首先我们从最基本的原理开始分析，看一张图：</p>    <p style="text-align: center;"><img src="https://simg.open-open.com/show/995a33da094ceb187d10de92428afbe9.png"></p>    <p>这个图该怎么绘制呢？实际上我们这里是先绘制两个圆，然后将两个圆的切点通过贝塞尔曲线连接起来就达到这个效果了。至于贝塞尔曲线的概念，这里就不多做解释了，百度一下就知道了。</p>    <p style="text-align: center;"><img src="https://simg.open-open.com/show/08f0a6b841028c4aabfab2a1819b85d4.png"></p>    <p>切点怎么算呢，这里我们稍微复习一些初中的数学知识。看了这个图之后，求出四个切点应该是轻而易举了。</p>    <p style="text-align: center;"><img src="https://simg.open-open.com/show/dacd20cf3fb83ebc15772bd90d243503.png"></p>    <p>现在思路已经很清晰了，按照我们的思路，开撸。</p>    <p>首先是我们计算切点以及各坐标点的工具类</p>    <pre>  <code class="language-java">public class GeometryUtils {      /**       * As meaning of method name.       * 获得两点之间的距离       * @param p0       * @param p1       * @return       */      public static float getDistanceBetween2Points(PointF p0, PointF p1) {          float distance = (float) Math.sqrt(Math.pow(p0.y - p1.y, 2) + Math.pow(p0.x - p1.x, 2));          return distance;      }        /**       * Get middle point between p1 and p2.       * 获得两点连线的中点       * @param p1       * @param p2       * @return       */      public static PointF getMiddlePoint(PointF p1, PointF p2) {          return new PointF((p1.x + p2.x) / 2.0f, (p1.y + p2.y) / 2.0f);      }        /**       * Get point between p1 and p2 by percent.       * 根据百分比获取两点之间的某个点坐标       * @param p1       * @param p2       * @param percent       * @return       */      public static PointF getPointByPercent(PointF p1, PointF p2, float percent) {          return new PointF(evaluateValue(percent, p1.x , p2.x), evaluateValue(percent, p1.y , p2.y));      }        /**       * 根据分度值，计算从start到end中，fraction位置的值。fraction范围为0 -> 1       * @param fraction       * @param start       * @param end       * @return       */      public static float evaluateValue(float fraction, Number start, Number end){          return start.floatValue() + (end.floatValue() - start.floatValue()) * fraction;      }        /**       * Get the point of intersection between circle and line.       * 获取 通过指定圆心，斜率为lineK的直线与圆的交点。       *       * @param pMiddle The circle center point.       * @param radius The circle radius.       * @param lineK The slope of line which cross the pMiddle.       * @return       */      public static PointF[] getIntersectionPoints(PointF pMiddle, float radius, Double lineK) {          PointF[] points = new PointF[2];            float radian, xOffset = 0, yOffset = 0;          if(lineK != null){              radian= (float) Math.atan(lineK);              xOffset = (float) (Math.sin(radian) * radius);              yOffset = (float) (Math.cos(radian) * radius);          }else {              xOffset = radius;              yOffset = 0;          }          points[0] = new PointF(pMiddle.x + xOffset, pMiddle.y - yOffset);          points[1] = new PointF(pMiddle.x - xOffset, pMiddle.y + yOffset);            return points;      }  }</code></pre>    <p>然后下面看下我们的核心绘制代码，代码注释比较全，此处就不多做解释了。</p>    <pre>  <code class="language-java">/**       * 绘制贝塞尔曲线部分以及固定圆       *       * @param canvas       */      private void drawGooPath(Canvas canvas) {          Path path = new Path();          //1. 根据当前两圆圆心的距离计算出固定圆的半径          float distance = (float) GeometryUtils.getDistanceBetween2Points(mDragCenter, mStickCenter);          stickCircleTempRadius = getCurrentRadius(distance);            //2. 计算出经过两圆圆心连线的垂线的dragLineK（对边比临边）。求出四个交点坐标          float xDiff = mStickCenter.x - mDragCenter.x;          Double dragLineK = null;          if (xDiff != 0) {              dragLineK = (double) ((mStickCenter.y - mDragCenter.y) / xDiff);          }            //分别获得经过两圆圆心连线的垂线与圆的交点（两条垂线平行，所以dragLineK相等）。          PointF[] dragPoints = GeometryUtils.getIntersectionPoints(mDragCenter, dragCircleRadius, dragLineK);          PointF[] stickPoints = GeometryUtils.getIntersectionPoints(mStickCenter, stickCircleTempRadius, dragLineK);            //3. 以两圆连线的0.618处作为 贝塞尔曲线 的控制点。（选一个中间点附近的控制点）          PointF pointByPercent = GeometryUtils.getPointByPercent(mDragCenter, mStickCenter, 0.618f);            // 绘制两圆连接闭合          path.moveTo((float) stickPoints[0].x, (float) stickPoints[0].y);          path.quadTo((float) pointByPercent.x, (float) pointByPercent.y,                  (float) dragPoints[0].x, (float) dragPoints[0].y);          path.lineTo((float) dragPoints[1].x, (float) dragPoints[1].y);          path.quadTo((float) pointByPercent.x, (float) pointByPercent.y,                  (float) stickPoints[1].x, (float) stickPoints[1].y);          canvas.drawPath(path, mPaintRed);          // 画固定圆          canvas.drawCircle(mStickCenter.x, mStickCenter.y, stickCircleTempRadius, mPaintRed);      }</code></pre>    <p>此时我们已经实现了绘制的核心代码，然后我们加上touch事件的监听，达到动态的更新dragPoint的中心点位置以及stickPoint半径的效果。当手抬起的时候，添加一个属性动画，达到回弹的效果。</p>    <pre>  <code class="language-java">@Override      public boolean onTouchEvent(MotionEvent event) {          switch (MotionEventCompat.getActionMasked(event)) {              case MotionEvent.ACTION_DOWN: {                  isOutOfRange = false;                  updateDragPointCenter(event.getRawX(), event.getRawY());                  break;              }              case MotionEvent.ACTION_MOVE: {                  //如果两圆间距大于最大距离mMaxDistance，执行拖拽结束动画                  PointF p0 = new PointF(mDragCenter.x, mDragCenter.y);                  PointF p1 = new PointF(mStickCenter.x, mStickCenter.y);                  if (GeometryUtils.getDistanceBetween2Points(p0, p1) > mMaxDistance) {                      isOutOfRange = true;                      updateDragPointCenter(event.getRawX(), event.getRawY());                      return false;                  }                  updateDragPointCenter(event.getRawX(), event.getRawY());                  break;              }              case MotionEvent.ACTION_UP: {                  handleActionUp();                  break;              }              default: {                  isOutOfRange = false;                  break;              }          }          return true;      }        /**       * 手势抬起动作       */      private void handleActionUp() {          if (isOutOfRange) {              // 当拖动dragPoint范围已经超出mMaxDistance，然后又将dragPoint拖回mResetDistance范围内时              if (GeometryUtils.getDistanceBetween2Points(mDragCenter, mStickCenter) < mResetDistance) {                  //reset                  return;              }              // dispappear          } else {              //手指抬起时，弹回动画              mAnim = ValueAnimator.ofFloat(1.0f);              mAnim.setInterpolator(new OvershootInterpolator(5.0f));                final PointF startPoint = new PointF(mDragCenter.x, mDragCenter.y);              final PointF endPoint = new PointF(mStickCenter.x, mStickCenter.y);              mAnim.addUpdateListener(new AnimatorUpdateListener() {                  @Override                  public void onAnimationUpdate(ValueAnimator animation) {                      float fraction = animation.getAnimatedFraction();                      PointF pointByPercent = GeometryUtils.getPointByPercent(startPoint, endPoint, fraction);                      updateDragPointCenter((float) pointByPercent.x, (float) pointByPercent.y);                  }              });              mAnim.addListener(new AnimatorListenerAdapter() {                  @Override                  public void onAnimationEnd(Animator animation) {                      //reset                  }              });                if (GeometryUtils.getDistanceBetween2Points(startPoint, endPoint) < 10) {                  mAnim.setDuration(100);              } else {                  mAnim.setDuration(300);              }              mAnim.start();          }      }</code></pre>    <p>此时我们拖拽的核心代码基本都已经完成，实际效果如下：</p>    <p style="text-align: center;"><img src="https://simg.open-open.com/show/a5a00af9c8408b87316fc5f1a41d9a07.gif"></p>    <p>现在小红点的绘制基本告一段落，我们不得不去思考真正的难点。那就是如何将我们前面的这个GooView应用到实际呢？看实际效果我们的小红点是放在listView里面的，如果是这样的话，就代表我们的GooView的拖拽范围是肯定无法超过父控件item的区域的。</p>    <p>那么我们要如何实现小红点可以随便的在整个屏幕拖拽呢？我们这里稍微整理一下思路。</p>    <p>1.先在listView的item布局中先放入一个小红点。</p>    <p>2.当我们touch到这个小红点的时候，隐藏这个小红点，然后根据我们布局中小红点的位置初始化一个GooView并且添加到WindowManager中吗，达到GooView可以全屏拖动的效果。</p>    <p>3.在添加GooView到WindowManager中的时候，记录初始小红点stickPoint的位置，然后根据stickPoint和dragPointde位置是否超出我们的消失界限来判断接下来的逻辑。</p>    <p>4.根据GooView的最终状态，显示回弹或者消失动画。</p>    <p>思路有了，那么就上代码，根据第一步，我们完成listView的item布局。</p>    <pre>  <code class="language-java"><?xml version="1.0" encoding="utf-8"?>  <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"                  android:layout_width="match_parent"                  android:layout_height="80dp"                  android:minHeight="80dp">        <ImageView          android:id="@+id/iv_head"          android:layout_width="50dp"          android:layout_height="50dp"          android:layout_centerVertical="true"          android:layout_marginLeft="20dp"          android:src="@mipmap/head"/>        <TextView          android:id="@+id/tv_content"          android:layout_width="wrap_content"          android:layout_height="50dp"          android:layout_centerVertical="true"          android:gravity="center"          android:layout_marginLeft="20dp"          android:layout_toRightOf="@+id/iv_head"          android:text="content - "          android:textSize="25sp"/>        <LinearLayout          android:id="@+id/ll_point"          android:layout_width="80dp"          android:layout_height="80dp"          android:layout_alignParentEnd="true"          android:layout_alignParentRight="true"          android:layout_alignParentTop="true"          android:gravity="center">            <TextView              android:id="@+id/point"              android:layout_width="wrap_content"              android:layout_height="18dp"              android:background="@drawable/red_bg"              android:gravity="center"              android:singleLine="true"              android:textColor="@android:color/white"              android:textSize="12sp"/>      </LinearLayout>  </RelativeLayout></code></pre>    <p>效果如下，要注意的是，对比QQ的真实体验，小红点周边范围点击的时候，都是可以直接拖拽小红点的。考虑到红点的点击范围比较小，所以给红点增加了一个宽高80dp的父layout，然后我们将touch小红点事件更改为touch小红点父layout，这样只要我们点击了小红点的父layout范围，都会添加GooView到WindowManager中。</p>    <p style="text-align: center;"><img src="https://simg.open-open.com/show/4265ba6e766218440d6c82d0b99c24f2.png"></p>    <p>接下来第二步，我们完成添加GooView到WindowManager中的代码。</p>    <p>由于我们的GooView初始添加是从listViewItem中红点的touch事件开始的，所以我们先完成listView adapter的实现。</p>    <pre>  <code class="language-java">public class GooViewAapter extends BaseAdapter {      private Context mContext;      //记录已经remove的position      private HashSet<Integer> mRemoved = new HashSet<Integer>();      private List<String> list = new ArrayList<String>();        public GooViewAapter(Context mContext, List<String> list) {          super();          this.mContext = mContext;          this.list = list;      }        @Override      public int getCount() {          return list.size();      }        @Override      public Object getItem(int position) {          return list.get(position);      }        @Override      public long getItemId(int position) {          return position;      }        @Override      public View getView(final int position, View convertView, ViewGroup parent) {          if (convertView == null) {              convertView = View.inflate(mContext, R.layout.list_item_goo, null);          }          ViewHolder holder = ViewHolder.getHolder(convertView);          holder.mContent.setText(list.get(position));          //item固定小红点layout          LinearLayout pointLayout = holder.mPointLayout;          //item固定小红点          final TextView point = holder.mPoint;            boolean visiable = !mRemoved.contains(position);          pointLayout.setVisibility(visiable ? View.VISIBLE : View.GONE);          if (visiable) {              point.setText(String.valueOf(position));              pointLayout.setTag(position);              GooViewListener mGooListener = new GooViewListener(mContext, pointLayout) {                  @Override                  public void onDisappear(PointF mDragCenter) {                      super.onDisappear(mDragCenter);                      mRemoved.add(position);                      notifyDataSetChanged();                      Utils.showToast(mContext, "position " + position + " disappear.");                  }                    @Override                  public void onReset(boolean isOutOfRange) {                      super.onReset(isOutOfRange);                      notifyDataSetChanged();//刷新ListView                      Utils.showToast(mContext, "position " + position + " reset.");                  }              };              //在point父布局内的触碰事件都进行监听              pointLayout.setOnTouchListener(mGooListener);          }          return convertView;      }        static class ViewHolder {            public ImageView mImage;          public TextView mPoint;          public LinearLayout mPointLayout;          public TextView mContent;            public ViewHolder(View convertView) {              mImage = (ImageView) convertView.findViewById(R.id.iv_head);              mPoint = (TextView) convertView.findViewById(R.id.point);              mPointLayout = (LinearLayout) convertView.findViewById(R.id.ll_point);              mContent = (TextView) convertView.findViewById(R.id.tv_content);          }            public static ViewHolder getHolder(View convertView) {              ViewHolder holder = (ViewHolder) convertView.getTag();              if (holder == null) {                  holder = new ViewHolder(convertView);                  convertView.setTag(holder);              }              return holder;          }      }  }</code></pre>    <p>由于listview需要知道GooView的状态，所以我们在GooView中增加一个接口，用于listView回调处理后续的逻辑。</p>    <pre>  <code class="language-java">interface OnDisappearListener {          /**           * GooView Disapper           *           * @param mDragCenter           */          void onDisappear(PointF mDragCenter);            /**           * GooView onReset           *           * @param isOutOfRange           */          void onReset(boolean isOutOfRange);        }</code></pre>    <p>新建一个实现了OnTouchListener以及OnDisappearListener 方法的的类，最后将这个实现类设置给item中的红点Layout。</p>    <pre>  <code class="language-java">public class GooViewListener implements OnTouchListener, OnDisappearListener {        private WindowManager mWm;      private WindowManager.LayoutParams mParams;      private GooView mGooView;      private View pointLayout;      private int number;      private final Context mContext;        private Handler mHandler;        public GooViewListener(Context mContext, View pointLayout) {          this.mContext = mContext;          this.pointLayout = pointLayout;          this.number = (Integer) pointLayout.getTag();            mGooView = new GooView(mContext);            mWm = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);          mParams = new WindowManager.LayoutParams();          mParams.format = PixelFormat.TRANSLUCENT;//使窗口支持透明度          mHandler = new Handler(mContext.getMainLooper());      }        @Override      public boolean onTouch(View v, MotionEvent event) {          int action = MotionEventCompat.getActionMasked(event);          // 当按下时，将自定义View添加到WindowManager中          if (action == MotionEvent.ACTION_DOWN) {              ViewParent parent = v.getParent();              // 请求其父级View不拦截Touch事件              parent.requestDisallowInterceptTouchEvent(true);                int[] points = new int[2];              //获取pointLayout在屏幕中的位置（layout的左上角坐标）              pointLayout.getLocationInWindow(points);              //获取初始小红点中心坐标              int x = points[0] + pointLayout.getWidth() / 2;              int y = points[1] + pointLayout.getHeight() / 2;              // 初始化当前点击的item的信息，数字及坐标              mGooView.setStatusBarHeight(Utils.getStatusBarHeight(v));              mGooView.setNumber(number);              mGooView.initCenter(x, y);              //设置当前GooView消失监听              mGooView.setOnDisappearListener(this);              // 添加当前GooView到WindowManager              mWm.addView(mGooView, mParams);              pointLayout.setVisibility(View.INVISIBLE);          }          // 将所有touch事件转交给GooView处理          mGooView.onTouchEvent(event);          return true;      }        @Override      public void onDisappear(PointF mDragCenter) {          //disappear 下一步完成      }        @Override      public void onReset(boolean isOutOfRange) {          // 当dragPoint弹回时，去除该View，等下次ACTION_DOWN的时候再添加          if (mWm != null && mGooView.getParent() != null) {              mWm.removeView(mGooView);          }      }  }</code></pre>    <p>这样下来，我们基本上完成了大部分功能，现在还差最后一步，就是GooView超出范围消失后的处理，这里我们用一个帧动画来完成爆炸效果。</p>    <pre>  <code class="language-java">public class BubbleLayout extends FrameLayout {      Context context;        public BubbleLayout(Context context) {          super(context);          this.context = context;      }        private int mCenterX, mCenterY;        public void setCenter(int x, int y) {          mCenterX = x;          mCenterY = y;          requestLayout();      }        @Override      protected void onLayout(boolean changed, int left, int top, int right,                              int bottom) {          View child = getChildAt(0);          // 设置View到指定位置          if (child != null && child.getVisibility() != GONE) {              final int width = child.getMeasuredWidth();              final int height = child.getMeasuredHeight();              child.layout((int) (mCenterX - width / 2.0f), (int) (mCenterY - height / 2.0f)                      , (int) (mCenterX + width / 2.0f), (int) (mCenterY + height / 2.0f));          }      }  }    @Override      public void onDisappear(PointF mDragCenter) {          if (mWm != null && mGooView.getParent() != null) {              mWm.removeView(mGooView);                //播放气泡爆炸动画              ImageView imageView = new ImageView(mContext);              imageView.setImageResource(R.drawable.anim_bubble_pop);              AnimationDrawable mAnimDrawable = (AnimationDrawable) imageView                      .getDrawable();                final BubbleLayout bubbleLayout = new BubbleLayout(mContext);              bubbleLayout.setCenter((int) mDragCenter.x, (int) mDragCenter.y - Utils.getStatusBarHeight(mGooView));                bubbleLayout.addView(imageView, new FrameLayout.LayoutParams(                      android.widget.FrameLayout.LayoutParams.WRAP_CONTENT,                      android.widget.FrameLayout.LayoutParams.WRAP_CONTENT));                mWm.addView(bubbleLayout, mParams);                mAnimDrawable.start();                // 播放结束后，删除该bubbleLayout              mHandler.postDelayed(new Runnable() {                  @Override                  public void run() {                      mWm.removeView(bubbleLayout);                  }              }, 501);          }      }</code></pre>    <p> </p>    <p> </p>    <p>项目主页：<a href="http://www.open-open.com/lib/view/home/1492743800659">http://www.open-open.com/lib/view/home/1492743800659</a></p>    <p> </p>