No internet Connection Alert Dialog box. NetworkCallback was already unregistered error

I am trying to create a no internet connection alert dialog box on my app, it works but app crashes afterwards.

> java.lang.IllegalArgumentException: NetworkCallback was already unregistered

public class MainActivity extends AppCompatActivity {
    
        private ConnectivityManager mCManager;
        private ConnectivityManager.NetworkCallback mCallback;
        private AlertDialog mDialog;
    
    
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            mCManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkRequest request = new NetworkRequest.Builder().build();
            mCallback = new ConnectivityManager.NetworkCallback() {
                @Override
                public void onLost(Network network) {
    
                    AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this, R.style.Theme_AppCompat_Dialog_Alert)
                            .setTitle("Oops!... No Internet Connection")
                            .setMessage("Check your WIFI or your Mobile Data")
                            .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                                @Override
                                public void onClick(DialogInterface dialog, int which) {
                                    
                                    finishAndRemoveTask();
                                }
                            });
    
                    mDialog = builder.show();
                }
    
                @Override
                public void onAvailable(Network network) {
    
                    if (mDialog != null) {
                        mDialog.dismiss();
                    }
                }
            };
           
            mCManager.registerNetworkCallback(request, mCallback);
        }
        @Override
        public void onStop() {
    
            mCManager.unregisterNetworkCallback(mCallback);
            super.onStop();
        }
    
    }

I declared this in my application manifest as shown below.

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

Your problem is that you're adding it in onCreate, but removing it in onStop. Adding/removing listeners should be done in the matching methods:

• onCreate/onDestroy
• onStart/onStop
• onResume/onPause

Since you only want to show when the user has the app open, you probably want to register in onStart and unregister in onStop. Just make sure to check if you want to display it initially in onStart as well.

Just add a try catch like thisto ignore the exception:

try {
    mCManager.unregisterNetworkCallback(mCallback);
} catch(Exception e) {
    // ignore
}