public static boolean isStarted;
    private WindowManager windowManager;
    private WindowManager.LayoutParams layoutParams;
    private View displayView;

    private Handler mHandler = new Handler();
    private Button accOn;
    private Button accOff;

    @Override
    public void onCreate() {
super.onCreate();
        windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
        layoutParams = new WindowManager.LayoutParams();
        layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
        layoutParams.format = PixelFormat.RGBA_8888;
        layoutParams.gravity = Gravity.CENTER | Gravity.TOP;
//        layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
        layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL;
        layoutParams.width = 250;
        layoutParams.height = 50;
        layoutParams.x = 500;
        layoutParams.y = 0;
    }

@Override
    public IBinder onBind(Intent intent) {
return null;
    }

@Override
    public int onStartCommand(Intent intent, int flags, int startId) {
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {//兼容android8.0以上需要启动前台服务
            NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
            NotificationChannel mChannel = new NotificationChannel("CHANNEL_ID_STRING", "检查连接状态", NotificationManager.IMPORTANCE_HIGH);
            notificationManager.createNotificationChannel(mChannel);
            Notification notification = new Notification.Builder(getApplicationContext(), "CHANNEL_ID_STRING").build();
            startForeground(1, notification);
        }
isStarted = true;
        showFloatingWindow();
        return super.onStartCommand(intent, flags, startId);
    }

private String address;
    private void showFloatingWindow() {
if (Settings.canDrawOverlays(this)) {
            LayoutInflater layoutInflater = LayoutInflater.from(this);
            displayView = layoutInflater.inflate(R.layout.window, null);
            accOn = displayView.findViewById(R.id.acc_on);
            accOn.setOnClickListener(new View.OnClickListener() {
@Override
                public void onClick(View view) {

                }
            });
            accOff = displayView.findViewById(R.id.acc_off);
            accOff.setOnClickListener(new View.OnClickListener() {
@Override
                public void onClick(View view) {
                    
                }
            });
            windowManager.addView(displayView, layoutParams);
        }
    }

android-windowManager使用实例