Flutter - Issue with callback function

Question

I've searched everywhere and can't find a simple solution. I'm new to coding and new to Flutter/Dart.

I suspect this is a very basic problem. I need to pass a callback via an intermediary widget to the final widget.

Overview of the issue:

RootPage > TabNavigator > SearchPage > ProfilePage(with logout button on ProfilePage). Does not work.

In RootPage the offending code is:

  @override
  Widget build(BuildContext context) {
    switch (authStatus) {
      case AuthStatus.notDetermined:
        return _buildWaitingScreen();
      case AuthStatus.notSignedIn:
        return LoginPage(
          onSignedIn: _signedIn,
        );
      case AuthStatus.signedIn:
        return TabNavigation(
          ProfilePage(onSignedOut: _signedOut,)
        );
    }
    return null;
  }

RootPage > SearchPage (logout button on this SearchPage). Does work with this code:

@override
  Widget build(BuildContext context) {
    switch (authStatus) {
      case AuthStatus.notDetermined:
        return _buildWaitingScreen();
      case AuthStatus.notSignedIn:
        return LoginPage(
          onSignedIn: _signedIn,
        );
      case AuthStatus.signedIn:
        return SearchPage(
          onSignedOut: _signedOut,
        );
    }
    return null;
  }

Code snippet:

class ProfilePage extends StatelessWidget {
  ProfilePage({this.onSignedOut});
  final VoidCallback onSignedOut;

 @override
    Widget build(BuildContext context) {
        return new Scaffold(
          appBar: new AppBar(
            title: new Text('Manage Profile'),
            actions: <Widget> [
              new FlatButton(
                child: new Text('Logout', style: new TextStyle(fontSize: 17.0, color: Colors.white)),
                onPressed: () => _signOut(context)
.....
....


class _RootPageState extends State<RootPage> {
  AuthStatus authStatus = AuthStatus.notDetermined;

@override
  Widget build(BuildContext context) {
    switch (authStatus) {
      case AuthStatus.notDetermined:
        return _buildWaitingScreen();
      case AuthStatus.notSignedIn:
        return LoginPage(
          onSignedIn: _signedIn,
        );
      case AuthStatus.signedIn:
        return TabNavigation(
          ProfilePage(onSignedOut: _signedOut), 
        );
    }
    return null;
  }

Homepage of my app is RootPage, which manages the user's login status. Once logged in, the RootPage returns TabNavigation, which is a utility that manages the bottomNavigationbar, and returns SearchPage by default (i.e. setState returns currentPage = SearchPage).

I now wish to have the logout button on ProfilePage.

I don't know how to get the onPressed callback function to pass it's output back to RootPage.

Difficult to explain without pasting in the full code, but I hope you get the concept.

Are you getting any error in the console?

Dinesh Balasubramanian
– Dinesh Balasubramanian

2018-08-23 04:44:58 +00:00
Commented Aug 23, 2018 at 4:44 — Dinesh Balasubramanian
– Dinesh Balasubramanian, Commented Aug 23, 2018 at 4:44
No, no errors in the console

Sam A
– Sam A

2018-08-23 08:02:07 +00:00
Commented Aug 23, 2018 at 8:02 — Sam A
– Sam A, Commented Aug 23, 2018 at 8:02

Ravi Varu · Accepted Answer · 2018-08-23 09:20:57Z

You can use an InheritedWidget at root level i.e. at _RootPageState class. Now you can pass any information(data) down at any point in hierarchy. In your case passed onPressed will get use at ProfilePage.

class LogoutAction extends InheritedWidget {
  const LogoutAction({
    Key key,
    @required this.logoutButtonClick,
    @required Widget child,
  }) : assert(logoutButtonClick != null),
       assert(child != null),
       super(key: key, child: child);

  final VoidCallback logoutButtonClick;

  static LogoutAction of(BuildContext context) {
    return context.inheritFromWidgetOfExactType(LogoutAction);
  }

  @override
  bool updateShouldNotify(LogoutAction old) => logoutButtonClick != old.logoutButtonClick;
}

now this LogoutAction widget can be used at

class _RootPageState extends State<RootPage> {
  AuthStatus authStatus = AuthStatus.notDetermined;

  _logoutClick() {
    //your code
  }

  @override
  Widget build(BuildContext context) {
    return LogoutAction(
      logoutButtonClick: _logoutClick,
      child: //todo: child widget that will use ProfilePage
    );
  }
}

and your logout button will look like:

FlatButton(
  onPressed: LogoutAction.of(context).logoutButtonClick
)

Dinesh Balasubramanian · Accepted Answer · 2018-08-23 04:57:44Z

0

As it is working in SearchPage, then it should be straightforward. Refer the below code,

class SearchPage extends StatefulWidget {
  final VoidCallback onSignedOut;

  SearchPage(this.onSignedOut); //getting from RootPage (might be via TabNavigator)

  @override
  State<StatefulWidget> createState() {
    return new _SearchPage();
  }

}

class _SearchPage extends State<SearchPage> {
  @override
  Widget build(BuildContext context) {
    var route = MaterialPageRoute(
        builder: (context) => ProfilePage(this.widget.onSignedOut)); // sending the callback to ProfilePage
    Navigator.push(context, route);
  }
}

class ProfilePage extends StatelessWidget {
  ProfilePage(this.onSignedOut);
  final VoidCallback onSignedOut;

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: new AppBar(
        title: new Text('Manage Profile'),
    actions: <Widget> [
    new FlatButton(
    child: new Text('Logout', style: new TextStyle(fontSize: 17.0, color: Colors.white)),
    onPressed: () => onSignedOut() //invoking the callback which will execute in RootPage
    //....
  }
}

Note: In your ProfilePage, onPressed method name looks wrong _signOut(context). If you are using some private method which calls onSignedOut that is fine. If not, you have to use onSignedOut()

answered Aug 23, 2018 at 4:57

Dinesh Balasubramanian

21.8k9 gold badges69 silver badges61 bronze badges

1 Comment

Sam A Over a year ago

Thanks for the response. This doesn't solve my problem. I've rewritten the question with additional detail and code snippets.

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