@Override
public boolean moveTaskToBack(boolean nonRoot) {
return super.moveTaskToBack(nonRoot);
}

public class FloatVideoWindowService extends Service {

 @Nullable
 @Override
 public IBinder onBind(Intent intent) {
  return new MyBinder();
 }

 public class MyBinder extends Binder {
  public FloatVideoWindowService getService() {
   return FloatVideoWindowService.this;
  }
 }

 @Override
 public void onCreate() {
  super.onCreate();
 }

 @Override
 public int onStartCommand(Intent intent, int flags, int startId) {
  return super.onStartCommand(intent, flags, startId);
 }

 @Override
 public void onDestroy() {
  super.onDestroy();
 }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:app="http://schemas.android.com/apk/res-auto"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content">

 <FrameLayout
  android:layout_width="80dp"
  android:layout_height="110dp"
  android:background="@color/black_1f2d3d">

  <LinearLayout
   android:id="@+id/small_size_preview"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:background="@color/transparent"
   android:orientation="vertical" />
 </FrameLayout>
</LinearLayout>

public class FloatVideoWindowService extends Service {
 private WindowManager mWindowManager;
 private WindowManager.LayoutParams wmParams;
 private LayoutInflater inflater;

 //constant
 private boolean clickflag;

 //view
 private View mFloatingLayout; //浮动布局
 private LinearLayout smallSizePreviewLayout; //容器父布局

 @Nullable
 @Override
 public IBinder onBind(Intent intent) {
  return new MyBinder();
 }

 public class MyBinder extends Binder {
  public FloatVideoWindowService getService() {
   return FloatVideoWindowService.this;
  }
 }

 @Override
 public void onCreate() {
  super.onCreate();
  initWindow();//设置悬浮窗基本参数（位置、宽高等）
  initFloating();//悬浮框点击事件的处理
 }

 @Override
 public int onStartCommand(Intent intent, int flags, int startId) {
  return super.onStartCommand(intent, flags, startId);
 }

 
 @Override
 public void onDestroy() {
  super.onDestroy();
 }

 /**
  * 设置悬浮框基本参数（位置、宽高等）
  */
 private void initWindow() {
  mWindowManager = (WindowManager) getApplicationContext().getSystemService(Context.WINDOW_SERVICE);
  wmParams = getParams();//设置好悬浮窗的参数
  // 悬浮窗默认显示以左上角为起始坐标
  wmParams.gravity = Gravity.LEFT | Gravity.TOP;
  //悬浮窗的开始位置，因为设置的是从左上角开始，所以屏幕左上角是x=0;y=0
  wmParams.x = 70;
  wmParams.y = 210;
  //得到容器，通过这个inflater来获得悬浮窗控件
  inflater = LayoutInflater.from(getApplicationContext());
  // 获取浮动窗口视图所在布局
  mFloatingLayout = inflater.inflate(R.layout.alert_float_video_layout, null);
  // 添加悬浮窗的视图
  mWindowManager.addView(mFloatingLayout, wmParams);
 }

 
 private WindowManager.LayoutParams getParams() {
  wmParams = new WindowManager.LayoutParams();
  //设置window type 下面变量2002是在屏幕区域显示，2003则可以显示在状态栏之上
  wmParams.type = WindowManager.LayoutParams.TYPE_TOAST;
  //设置可以显示在状态栏上
  wmParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL |
    WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN | WindowManager.LayoutParams.FLAG_LAYOUT_INSET_DECOR |
    WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH;

  //设置悬浮窗口长宽数据
  wmParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
  wmParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
  return wmParams;
 }

　　
 private void initFloating() {
  smallSizePreviewLayout = mFloatingLayout.findViewById(R.id.small_size_preview);

  //悬浮框点击事件
  smallSizePreviewLayout.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
    　//在这里实现点击重新回到Activity
   }
  });

  //悬浮框触摸事件，设置悬浮框可拖动
  smallSizePreviewLayout.setOnTouchListener(new FloatingListener());
 }

 //开始触控的坐标，移动时的坐标（相对于屏幕左上角的坐标）
 private int mTouchStartX, mTouchStartY, mTouchCurrentX, mTouchCurrentY;
 //开始时的坐标和结束时的坐标（相对于自身控件的坐标）
 private int mStartX, mStartY, mStopX, mStopY;
　　 //判断悬浮窗口是否移动，这里做个标记，防止移动后松手触发了点击事件
 private boolean isMove;

 private class FloatingListener implements View.OnTouchListener {

  @Override
  public boolean onTouch(View v, MotionEvent event) {
   int action = event.getAction();
   switch (action) {
    case MotionEvent.ACTION_DOWN:
     isMove = false;
     mTouchStartX = (int) event.getRawX();
     mTouchStartY = (int) event.getRawY();
     mStartX = (int) event.getX();
     mStartY = (int) event.getY();
     break;
    case MotionEvent.ACTION_MOVE:
     mTouchCurrentX = (int) event.getRawX();
     mTouchCurrentY = (int) event.getRawY();
     wmParams.x += mTouchCurrentX - mTouchStartX;
     wmParams.y += mTouchCurrentY - mTouchStartY;
     mWindowManager.updateViewLayout(mFloatingLayout, wmParams);

     mTouchStartX = mTouchCurrentX;
     mTouchStartY = mTouchCurrentY;
     break;
    case MotionEvent.ACTION_UP:
     mStopX = (int) event.getX();
     mStopY = (int) event.getY();
     if (Math.abs(mStartX - mStopX) >= 1 || Math.abs(mStartY - mStopY) >= 1) {
      isMove = true;
     }
     break;
   }

   //如果是移动事件不触发OnClick事件，防止移动的时候一放手形成点击事件
   return isMove;
  }
 }
}

/**
  * 初始化预览窗口
  */
 private void initSurface() {
  if (smallRender == null) {
   smallRender = new AVChatSurfaceViewRenderer(getApplicationContext());
  }

  addIntoSmallSizePreviewLayout(smallRender);
 }

 /**
  * 添加surfaceview到smallSizePreviewLayout
  */
 private void addIntoSmallSizePreviewLayout(SurfaceView surfaceView) {
  if (surfaceView.getParent() != null) {
   ((ViewGroup) surfaceView.getParent()).removeView(surfaceView);
  }

  smallSizePreviewLayout.addView(surfaceView);
  surfaceView.setZOrderMediaOverlay(true);
 }

@Override
 public void onDestroy() {
  super.onDestroy();
  if (mFloatingLayout != null) {
   // 移除悬浮窗口
   mWindowManager.removeView(mFloatingLayout);
  }

  //清除视频画布
  AVChatManager.getInstance().setupRemoteVideoRender(account, null, false, 0);
 }

intent = new Intent(this, FloatVideoWindowService.class);//开启服务显示悬浮框
bindService(intent, mVideoServiceConnection, Context.BIND_AUTO_CREATE);

ServiceConnection mVideoServiceConnection = new ServiceConnection() {

  @Override
  public void onServiceConnected(ComponentName name, IBinder service) {
   // 获取服务的操作对象
   FloatVideoWindowService.MyBinder binder = (FloatVideoWindowService.MyBinder) service;
   binder.getService();
  }

  @Override
  public void onServiceDisconnected(ComponentName name) {
  }
 };

public void startVideoService() {
   moveTaskToBack(true);//最小化Activity
   intent = new Intent(this, FloatVideoWindowService.class);//开启服务显示悬浮框
   bindService(intent, mVideoServiceConnection, Context.BIND_AUTO_CREATE);
 }

@Override
 protected void onRestart() {
  super.onRestart();
  unbindService(mVideoServiceConnection);//不显示悬浮框

  //从悬浮窗进来后重新设置画布(判断是不是接通了)
  if (isCallEstablished) {
   //如果接通，先清除所有画布
   avChatUI.clearAllSurfaceView(avChatUI.getAccount());
   //延迟重新加载远端和本地的视频画布
   mHandler.postDelayed(new Runnable() {
    @Override
    public void run() {
     avChatUI.initAllSurfaceView(avChatUI.getAccount());
     
    }
   }, 800);
  } else {
   //如果没接通，直接初始化所有画布
   avChatUI.initLargeSurfaceView(IMCache.getAccount());
  }
 }