Open flutter dialog after navigation

Another way of doing it is using Timer.run(...)

@override
void initState() {
  super.initState();

  // simply use this
  Timer.run(() {
    showDialog(
      context: context,
      builder: (_) => AlertDialog(title: Text("Dialog title")),
    );
  });
}

You can call the dialog from inside 'initState()' dalaying its appearance after the first frame has been drawn.

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_) async {
      await showDialog<String>(
        context: context,
        builder: (BuildContext context) => new AlertDialog(
              title: new Text("title"),
              content: new Text("Message"),
              actions: <Widget>[
                new FlatButton(
                  child: new Text("OK"),
                  onPressed: () {
                    Navigator.of(context).pop();
                  },
                ),
              ],
            ),
      );
    });
  }

The context variable is always available inside the State class. It points to the RenderObject of this widget. The problem is that in initState() the context is not yet created so you have to defer its usage after the first frame has been laid out. Then it is available.

If anyone after a solution to display dialog based on the widget value update.

For example, let users know the screen they are trying to view, has been deleted.

if (xxx.timestamps.deleted == null) {
  return DetailView(xxx: xxx);
} else {
  return FutureBuilder(
    future: Future.delayed(
      Duration.zero,
      () => showDialog(
          context: context,
          builder: (_) => ActionDialog(
              title: Text('xxx Deleted'),
              content: Text('xxx deleted'),
              confirmActions: [DialogConfirm.Ok])).then(
        (value) => Navigator.pop(context),
      ),
    ),
    builder: (context, _) => DetailView(xxx: xxx),
  );
}

kudos to https://stackoverflow.com/a/64017240/2641128