AlertDialog without context in Flutter

Question

I want to show an AlertDialog when a http get fails. The function showDialog (https://api.flutter.dev/flutter/material/showDialog.html) has the parameter "@required BuildContext context", but I want to call the AlertDialog from my async function getNews(), which hasn't a context value.

By analogy with Java, where I use null for dialog without an owner, I tried to put context value to null, but it is not accepted.

This is my code:

  Future<dynamic> getNews() async {
    dynamic retVal;
    try {
      var response = await http.get(url));
      if (response.statusCode == HttpStatus.ok) {
        retVal = jsonDecode(response.body);
      }
    } catch (e) {
      alertDlg(?????????, 'Error', e.toString());
  }
    return
    retVal;
  }

  static Future<void> alertDlg(context, String titolo, String messaggio) async {
    return showDialog<void>(
        context: context,
        barrierDismissible: false, // user must tap button!
        builder: (BuildContext context) {
        return AlertDialog(
              title: Text(titolo),
        ...
    );
  }

Pass your Build context from StatefulWidget where you'll display the http response to your getNews() function . — Mazin Ibrahim
– Mazin Ibrahim, Commented May 23, 2019 at 18:12
can you give an example please. I tried passing context to my new widget. It doesnt give any error but also doesnt show any alert — Aseem
– Aseem, Commented Jan 16, 2020 at 3:53
bypassing null not getting any compile time error but getting same Failed assertion: line 'context != null': is not true. — s.j
– s.j, Commented Oct 5, 2020 at 10:19

Igor Kharakhordin · Accepted Answer · 2020-10-07 08:17:20Z

135

Solution without third-party libraries or storing BuildContext:

final navigatorKey = GlobalKey<NavigatorState>();

void main() => runApp(
  MaterialApp(
    home: HomePage(),
    navigatorKey: navigatorKey, // Setting a global key for navigator
  ),
);

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: SafeArea(
        child: Center(
          child: Text('test')
        )
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: showMyDialog, // Calling the function without providing it BuildContext
      ),
    );
  }
}

void showMyDialog() {
  showDialog(
    context: navigatorKey.currentContext,
    builder: (context) => Center(
      child: Material(
        color: Colors.transparent,
        child: Text('Hello'),
      ),
    )
  );
}

After setting a global key for navigator (navigatorKey parameter of MaterialApp class), its current state becomes accessible from any part of the code. We can pass its context to the showDialog function. Make sure not to use it before the first frame is built, otherwise the state will be null.

Basically, dialogs are just another type of routes like MaterialPageRoute or CupertinoPageRoute - they are all derived from the ModalRoute class and their instances are pushed into NavigatorState. Context is only needed to get the current navigator's state. A new route can be pushed without having a context if we have a global navigator key:

navigatorKey.currentState.push(route)

Unfortunately, _DialogRoute class (...\flutter\lib\src\widgets\routes.dart) used in showDialog function is private and unaccessible, but you make your own dialog route class and push it into the navigator's stack.

UPDATE: Navigator.of method has been updated and it's no longer needed to pass subtree context.

edited Oct 7, 2020 at 8:17

answered May 13, 2020 at 11:45

Igor Kharakhordin

9,9833 gold badges43 silver badges41 bronze badges

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14 Comments

ch271828n Over a year ago

Great hack! The .overlay saved my day! (I found that if directly use navigatorKey.currentState.context, it will not work because the showDialog needs a context below the Navigator context.)

Magnus Over a year ago

How about using navigatorKey.currentContext? It seems to work, but I'm not sure if there are potential problems compared to currentState.overlay.context?

Ivan Yoed Over a year ago

If you're sure your navigatorKey will already have a context by the time you want to show the dialog, force unwrap your currentContext variable like so context: navigatorKey.currentContext!

Clifton Labrum Over a year ago

Is there something you can do to ensure that currentContext is not null early in the initialization of your app? I get nervous every time I put a ! in my code. 😅

queen3 Over a year ago

I get error "No Material widget found. ListTile widgets require a Material widget ancestor." when I try to create a dialog with that currentContext.

|

NecroMancer · Accepted Answer · 2022-12-12 13:51:06Z

11

The dialog only needs the context to access it through an inherited navigateState. You can make your own modified dialog, or use my lib to do this.

https://pub.dev/packages/get

With it you can open dialog from anywhere in your code without context by doing this:

Get.dialog(SimpleDialog());

edited Dec 12, 2022 at 13:51

NecroMancer

63611 silver badges18 bronze badges

answered Mar 31, 2020 at 17:10

jonatas Borges

2,26716 silver badges17 bronze badges

11 Comments

jonatas Borges Over a year ago

That's not possible. You probably forgot to add "Get" to your MaterialApp. Change it to GetMaterialApp and everything will work.

s.j Over a year ago

like this GetMaterialApp.dialog(SimpleDialog());

s.j Over a year ago

i tried this GetMaterialApp(title: UtilString.submit); getting compile time error.

cs guy Over a year ago

dont force a 3rd party lib if it is not needed. see the answer with final navigatorKey = GlobalKey<NavigatorState>();

jonatas Borges Over a year ago

The correct answer (now deleted) said "There is no way to do this in Flutter". I'm not pushing GetX anywhere, I just mentioned that it's possible to do this, just like GetX does. The most voted answer came long after my answer, just compare the dates.

|

ZeRj · Accepted Answer · 2019-05-23 18:31:04Z

1

Catch the exception where you make the getNews call if you use await, else use the catchError property of the Future.

answered May 23, 2019 at 18:31

ZeRj

1,7381 gold badge14 silver badges24 bronze badges

Comments

Kirill Karmazin · Accepted Answer · 2020-02-27 14:42:18Z

1

So you need a BuildContext to create a dialog but you don't have access to it. That's a common problem, you can refer to this StackOverflow question for one of the approaches to solve it (create a static dialog and show it from wherever you need).

Another approach you may consider is to pass the context when creating an async method or object as an argument. Make sure you null it when you're done.

Or you can make a flag (boolean) which becomes 'true' under a certain condition, and in one of the build() methods you always check that flag, and if it's 'true' - do your thing (show a dialog for instance).

answered Feb 27, 2020 at 14:42

Kirill Karmazin

6,8412 gold badges59 silver badges44 bronze badges

Comments

Blastfurnace · Accepted Answer · 2023-05-03 23:57:36Z

Install GetX with: flutter pub add get
create a dialog with Get.dialog
add these line

Get.dialog(
      Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Padding(
            padding: const EdgeInsets.symmetric(horizontal: 40),
            child: Container(
              decoration: const BoxDecoration(
                color: Colors.white,
                borderRadius: BorderRadius.all(
                  Radius.circular(20),
                ),
              ),
              child: Padding(
                padding: const EdgeInsets.all(20.0),
                child: Material(
                  child: Column(
                    children: [
                      const Text("Dialog with GetX without context")
                      Row(
                        children: [
                          const SizedBox(width: 10),
                          Expanded(
                            child: ElevatedButton(
                              style: ElevatedButton.styleFrom(
                                minimumSize: const Size(0, 45),
                                primary: Colors.green,
                                onPrimary: const Color(0xFFFFFFFF),
                                shape: RoundedRectangleBorder(
                                  borderRadius: BorderRadius.circular(8),
                                ),
                              ),
                              onPressed: () {
                                Navigator.pop(Get.overlayContext!, true);
                              },
                              child: const Text(
                                'Cerrar',
                              ),
                            ),
                          ),
                        ],
                      ),
                    ],
                  ),
                ),
              ),
            ),
          ),
        ],
      ),
    );

done!

user3107831 · Accepted Answer · 2022-12-28 13:01:30Z

-5

Easiest way to show alert anywhere: Use this package link and enter these lines wherever you want to show alert:

QuickAlert.show( context: context, type: QuickAlertType.error, text: 'Error Message');

edited Dec 28, 2022 at 13:01

answered Dec 28, 2022 at 12:51

user3107831

853 bronze badges

3 Comments

Stephan Over a year ago

But your solution with QuickAlert needs a BuildContext context. The question was about "AlertDialog without context".

user3107831 Over a year ago

I request you to please read the question carefully not just the heading. Secondly I didn't provide the context from the Build method of the class. I just provided the type of alert and the text.

user3107831 Over a year ago

void showAlert(type, text) { QuickAlert.show( context: context, type: type, text: text, ); }

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