Flutter: Consider canceling any active work during "dispose" when internet changes its state

Question

I am getting the following message when internet goes off.

E/flutter (26162): [ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: This widget has been unmounted, so the State no longer has a context (and should be considered defunct).
E/flutter (26162): Consider canceling any active work during "dispose" or using the "mounted" getter to determine if the State is still active.

It is showing the message from this section of my code.

@override
  void initState() {
    super.initState();
    try {
      InternetAddress.lookup('google.com').then((result) {
        if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
          // internet conn available

          Navigator.of(context).pushReplacement(MaterialPageRoute(
            builder: (context) =>
                (Constants.prefsMobile.getString("mobile") == null
                    ? Login()
                    // : SignupPayoutPassword(signupdata: [])),
                    : Home(signindata: signinData)),
          ));
        } else {
          // no conn
          _showdialog();
        }
      }).catchError((error) {
        // no conn
        _showdialog();
      });
    } on SocketException catch (_) {
      // no internet
      _showdialog();
    }

    Connectivity()
        .onConnectivityChanged
        .listen((ConnectivityResult connresult) {
      if (connresult == ConnectivityResult.none) {
      } else if (previous == ConnectivityResult.none) {
        // internet conn
        Navigator.of(context).pop();
        Navigator.of(context).pushReplacement(MaterialPageRoute(
          builder: (context) =>
              (Constants.prefsMobile.getString("mobile") == null
                  ? Login()
                  : Home(signindata: signinData)),
        ));
      }

      previous = connresult;
    });
  }

I have not used any dispose method for this. If any one know please let me know how can I solve this problem. How to dispose. I am getting a crash report after my app close as follows

E/AndroidRuntime( 8064): java.lang.RuntimeException: Unable to destroy activity {com.example.aa_store/com.example.aa_store.MainActivity}: java.lang.IllegalArgumentException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter activity

is this crash message for the above problem? Please help.

user_13558035 · Answer

Please use.

@override
  void dispose() {
    Connectivity().onConnectivityChanged.cancel();
    super.dispose();
  }

Better, define your stream outside the initState:

Stream _connectivityStream = Connectivity().onConnectivityChanged;

and in dispose use _connectivityStream.cancel();.

The error means that you instantiated a stream, which on changes of events, triggers build changes. This stream is setup during initState, meaning when the widget is first created. Connectivity().onConnectivityChanged.listen(....etc).

But you never tell flutter to cancel listening to this stream when the widget is disposed.

This is the role of the dispose method. Similar to how you want logic to be performed when the widget is built, you use initState, you should also tell it when you are no longer interested in these changes in logic.

Failing to do so, will result in the error you are having, aside from memory leaks also.

This is the translation of the error This widget has been unmounted, so the State no longer has a context (and should be considered defunct). which you posted. "Hey, this widget isn't in the tree anymore, its state is not mounted, I can't rebuild it, and you need to pay attention to it.

Please consider using the dispose method for these Flutter elements, not to mention all of them, but from the top of my mind:

AnimationControllers.
Timers.
Streams listeners.

Flutter: Consider canceling any active work during "dispose" when internet changes its state

1 Answers