getLastKnownLocation 在 android 11 及更高版本的设备中返回 null

Question

位置未捕获在 Android 11 及更高版本的后台运行的应用程序，但它在 android 10 以下运行。我也包含了后台权限，但无法正常工作。 当应用程序在后台运行时，getLastKnownLocation retrun null，但应用程序打开重新运行位置此问题仅发生在 android 11 及以上设备这里是我的代码

     private void fn_getlocation() {

     locationManager = (LocationManager) getApplicationContext().getSystemService(LOCATION_SERVICE);

      isNetworkEnable = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);


        location = null;
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                return;
            }

    locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 1000, 0, this);

        if (locationManager != null) {
            location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
            if (location != null) {
               
                latitude = location.getLatitude();
                longitude = location.getLongitude();

                fn_update(location);
            }
        }


    }
    manifest file;    
     <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
     <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION" />