1.准备工作

   //检测并请求窗口弹窗权限，切记在清单注册
   <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

//检测窗口权限是否开启
  private boolean isPermissionOpen() {
        boolean isPermission = false;
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M) {
            isPermission = Settings.canDrawOverlays(this);
        }
        if (!isPermission)
            requestOverlayPermission();
        return isPermission;
    }

//如未开启，申请打开窗口权限
   private void requestOverlayPermission() {
        if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.M) {
            return;
        }
        Intent myIntent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION);
        myIntent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
        myIntent.setData(Uri.parse("package:" + getPackageName()));
        startActivityForResult(myIntent, REQUEST_SETTING_WINDOW);
    }

2.实现悬浮（必须有view）

    private void showFloatingWindow(View view) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (Settings.canDrawOverlays(this)) {
                // 获取WindowManager服务
                ViewGroup.LayoutParams params = view.getLayoutParams();
                params.height = ViewGroup.LayoutParams.MATCH_PARENT;
                params.width = ViewGroup.LayoutParams.MATCH_PARENT;
                view.setLayoutParams(params);
                windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);

//                roteImageView((ImageView) displayView.findViewById(R.id.image_change));
                // 设置LayoutParam
                WindowManager.LayoutParams layoutParams = new WindowManager.LayoutParams();
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                    layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
                } else {
                    layoutParams.type = WindowManager.LayoutParams.TYPE_PHONE;
                }
                layoutParams.format = PixelFormat.RGBA_8888;
                layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | FLAG_NOT_TOUCHABLE;
                // 将悬浮窗控件添加到WindowManager
                windowManager.addView(displayView, layoutParams);

                DisplayMetrics dm = new DisplayMetrics();
                windowManager.getDefaultDisplay().getMetrics(dm);
                int width = dm.widthPixels;
                int height = dm.heightPixels;

                Intent main = new Intent(Intent.ACTION_MAIN);
                main.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                main.addCategory(Intent.CATEGORY_HOME);
                startActivity(main);
            }
        }
    }

完结~