权限-悬浮窗

                // 找到布局文件
                View popup = LayoutInflater.from(getApplicationContext()).inflate(R.layout.popup, null);
                WindowManager mWindowManager = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
                // WindowManager.LayoutParams的参数
                WindowManager.LayoutParams mViewParams = new WindowManager.LayoutParams();
                mViewParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
                mViewParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
                mViewParams.gravity = Gravity.CENTER;
                DisplayMetrics dm = new DisplayMetrics();
                mWindowManager.getDefaultDisplay().getMetrics(dm);
                mViewParams.x = -(int) dm.widthPixels / 2;
                mViewParams.y = -(int) dm.heightPixels / 2;
                // 8.0系统加强后台管理，禁止在其他应用和窗口弹提醒弹窗，如果要弹，必须使用TYPE_APPLICATION_OVERLAY
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                    mViewParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
                } else {
                    mViewParams.type = WindowManager.LayoutParams.TYPE_SYSTEM_ERROR;
                }
                mViewParams.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                        | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                        | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
                        | WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
                        | WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON;
                mViewParams.format = PixelFormat.RGBA_8888;
                mViewParams.alpha = 0.5f;
                mWindowManager.addView(popup, mViewParams);