无法使用意图启动服务，无法添加窗口--内标识null无效，您的活动是否正在运行？

if (!isFinishing() && !isDestroyed()) {
    // 启动服务或添加窗口的操作
}

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
    if (!Settings.canDrawOverlays(this)) {
        Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
                Uri.parse("package:" + getPackageName()));
        startActivityForResult(intent, REQUEST_CODE);
    }
}

Intent serviceIntent = new Intent(this, MyService.class);
startService(serviceIntent);

WindowManager windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
View view = new View(this);
WindowManager.LayoutParams params = new WindowManager.LayoutParams(
        WindowManager.LayoutParams.WRAP_CONTENT,
        WindowManager.LayoutParams.WRAP_CONTENT,
        WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY,
        WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
        PixelFormat.TRANSLUCENT);

windowManager.addView(view, params);

public class MyService extends Service {
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // 执行后台任务
        return START_NOT_STICKY;
    }

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

Intent serviceIntent = new Intent(this, MyService.class);
startService(serviceIntent);