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Improve error message for type error in maybePop()/pop() #16987

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#186571
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Improve error message for type error in maybePop()/pop()#16987
#186571
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puneetkukreja98
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P2Important issues not at the top of the work lista: error messageError messages from the Flutter frameworkc: crashStack traces logged to the consolef: routesNavigator, Router, and related APIs.found in release: 3.7Found to occur in 3.7found in release: 3.8Found to occur in 3.8frameworkflutter/packages/flutter repository. See also f: labels.has reproducible stepsThe issue has been confirmed reproducible and is ready to work onteam-frameworkOwned by Framework teamtriaged-frameworkTriaged by Framework team

Description

@artAst
artAst
opened on Apr 26, 2018

Steps to Reproduce

Create a new project and have this pop-up box:

return showDialog<Null>(
    context: context,
    barrierDismissible: false, // user must tap button!
    child: new AlertDialog(
      title: new Text(title),
      content: new SingleChildScrollView(
        child: new ListBody(
          children: <Widget>[
            new Text(msg)
          ],
        ),
      ),
      actions: <Widget>[
        new FlatButton(
          child: new Text('NO'),
          onPressed: () {
            //Navigator.pop(context, "CANCEL");
            Navigator.maybePop(context, "CANCEL");
          },
        ),
        new FlatButton(
          child: new Text('YES'),
          onPressed: () {
            //Navigator.pop(context, "OK");
            Navigator.maybePop(context, "CANCEL");
          },
        ),
      ],
    ),
  ).then((val){
    return val;
  });

Once the cancel or OK button is clicked, it generates an error

Logs

E/flutter ( 4523): [ERROR:topaz/lib/tonic/logging/dart_error.cc(16)] Unhandled exception:
E/flutter ( 4523): type 'String' is not a subtype of type 'Null' of 'result' where
E/flutter ( 4523):   String is from dart:core
E/flutter ( 4523):   Null is from dart:core
E/flutter ( 4523): 
E/flutter ( 4523): #0      _ModalRoute&TransitionRoute&LocalHistoryRoute.didPop (package:flutter/src/widgets/routes.dart)
E/flutter ( 4523): #1      NavigatorState.pop (package:flutter/src/widgets/navigator.dart:1683:15)
E/flutter ( 4523): #2      NavigatorState.maybePop (package:flutter/src/widgets/navigator.dart:1648:9)
E/flutter ( 4523): <asynchronous suspension>
E/flutter ( 4523): #3      Navigator.maybePop (package:flutter/src/widgets/navigator.dart:1024:34)
E/flutter ( 4523): #4      showMainFrameDialogWithCancel.<anonymous closure> (package:myapp/src/util/ScreenUtils.dart:1334:23)
E/flutter ( 4523): #5      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:490:14)
E/flutter ( 4523): #6      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:545:30)
E/flutter ( 4523): #7      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:102:24)
E/flutter ( 4523): #8      TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:161:9)
E/flutter ( 4523): #9      TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:94:7)
E/flutter ( 4523): #10     PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:315:9)
E/flutter ( 4523): #11     PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:73:12)
E/flutter ( 4523): #12     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:11)
E/flutter ( 4523): #13     _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:143:19)
E/flutter ( 4523): #14     _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:121:22)
E/flutter ( 4523): #15     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:101:7)
E/flutter ( 4523): #16     _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:64:7)
E/flutter ( 4523): #17     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:48:7)
E/flutter ( 4523): #18     _invoke1 (dart:ui/hooks.dart:134:13)
E/flutter ( 4523): #19     _dispatchPointerDataPacket (dart:ui/hooks.dart:91:5)

Flutter Doctor

[✓] Flutter (Channel dev, v0.3.0, on Mac OS X 10.13.4 17E199, locale en-PH)
    • Flutter version 0.3.0 at /Users/macbook/Documents/flutter
    • Framework revision c73b8a7cf6 (13 days ago), 2018-04-12 16:17:26 -0700
    • Engine revision 8a6e64a8ef
    • Dart version 2.0.0-dev.47.0.flutter-4126459025

[!] Android toolchain - develop for Android devices (Android SDK 26.0.3)
    • Android SDK at /Users/macbook/Library/Android/sdk
    • Android NDK at /Users/macbook/Library/Android/sdk/ndk-bundle
    • Platform android-27, build-tools 26.0.3
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)
    ! Some Android licenses not accepted.  To resolve this, run: flutter doctor --android-licenses

[✓] iOS toolchain - develop for iOS devices (Xcode 9.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 9.3, Build version 9E145
    • ios-deploy 1.9.2
    • CocoaPods version 1.3.1

[✓] Android Studio (version 2.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] IntelliJ IDEA Community Edition (version 2017.2.5)
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • Flutter plugin version 19.1
    • Dart plugin version 172.4343.25

[!] VS Code (version 1.17.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Dart Code extension not installed; install from
      https://marketplace.visualstudio.com/items?itemName=Dart-Code.dart-code

[✓] Connected devices (1 available)
    • Android SDK built for x86 • emulator-5554 • android-x86 • Android 7.0 (API 24) (emulator)

Activity

  1. zoechi commented on Apr 26, 2018

    @zoechi
    zoechi
    on Apr 26, 2018
    Contributor

    with recent flutter update

    Your Flutter version is already 2 weeks old. Have you tried with a more recent one?

  2. artAst commented on Apr 26, 2018

    @artAst
    artAst
    on Apr 26, 2018
    Author

    I updated Flutter:

    [✓] Flutter (Channel dev, v0.3.5, on Mac OS X 10.13.4 17E199, locale en-PH)
    • Flutter version 0.3.5 at /Users/macbook/Documents/flutter
    • Framework revision 7ffcd3d22d (5 days ago), 2018-04-24 14:03:41 -0700
    • Engine revision ec611470b5
    • Dart version 2.0.0-dev.48.0.flutter-fe606f890b

[✓] Android toolchain - develop for Android devices (Android SDK 28.0.0-rc1)
    • Android SDK at /Users/macbook/Library/Android/sdk
    • Android NDK at /Users/macbook/Library/Android/sdk/ndk-bundle
    • Platform android-27, build-tools 28.0.0-rc1
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)
    • All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 9.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 9.3, Build version 9E145
    • ios-deploy 1.9.2
    • CocoaPods version 1.3.1

[✓] Android Studio (version 2.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] IntelliJ IDEA Community Edition (version 2017.2.5)
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • Flutter plugin version 19.1
    • Dart plugin version 172.4343.25

[!] VS Code (version 1.17.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Dart Code extension not installed; install from
      https://marketplace.visualstudio.com/items?itemName=Dart-Code.dart-code

[✓] Connected devices (1 available)
    • Android SDK built for x86 • emulator-5554 • android-x86 • Android 7.0 (API 24) (emulator)

    But still experiencing the same issue

  3. rodydavis commented on Apr 30, 2018

    @rodydavis
    rodydavis
    on Apr 30, 2018
    Contributor

    Just started experiencing this

  4. artAst commented on Apr 30, 2018

    @artAst
    artAst
    on Apr 30, 2018
    Author

    Still experiencing this issue with Flutter v0.3.5
    any inputs on this for later version releases?

  5. rodydavis commented on Apr 30, 2018

    @rodydavis
    rodydavis
    on Apr 30, 2018
    Contributor

    @artAst in the gallery example it uses a enum for the alert types. I wonder if it's something to do with just passing a string.

    enum DialogDemoAction {
  cancel,
  discard,
  disagree,
  agree,
}

    Then present

    showDemoDialog<DialogDemoAction>(
                context: context,
                child: new AlertDialog(
                  content: new Text(
                    _alertWithoutTitleText,
                    style: dialogTextStyle
                  ),
                  actions: <Widget>[
                    new FlatButton(
                      child: const Text('CANCEL'),
                      onPressed: () { Navigator.pop(context, DialogDemoAction.cancel); }
                    ),
                    new FlatButton(
                      child: const Text('DISCARD'),
                      onPressed: () { Navigator.pop(context, DialogDemoAction.discard); }
                    )
                  ]
                )
              );

  6. artAst commented on May 1, 2018

    @artAst
    artAst
    on May 1, 2018
    Author

    It did solve the issue. I also passed in the String object and it works as well. Thanks

    This was not present on previous version of flutter with Dart 1.0

  7. Hixie commented on Jun 12, 2018

    @Hixie
    Hixie
    on Jun 12, 2018
    Contributor

    The problem is that you said you were returning a Null (the type argument to showDialog), but then you passed a String.

    We should definitely make these error messages clear.

  8. Hixie
    changed the title [-]Navigator pop or maybe pop error with recent flutter update[/-] [+]Improve error message for type error in maybePop()/pop()[/+] on Jun 12, 2018
  9. Hixie
    added
    c: crashStack traces logged to the console
    frameworkflutter/packages/flutter repository. See also f: labels.
    f: routesNavigator, Router, and related APIs.
    on Jun 12, 2018
  10. Hixie
    added this to the milestone on Jun 12, 2018
  11. Piinks
    added
    a: error messageError messages from the Flutter framework
    on Nov 11, 2019
  12. kf6gpe
    added
    P2Important issues not at the top of the work list
    on May 29, 2020
  13. Hixie
    removed this from the milestone on Aug 17, 2020

  14. 9 remaining items

  15. flutter-triage-bot
    added
    triaged-frameworkTriaged by Framework team
    on Jul 8, 2023

  16. Piinks commented on May 13, 2026

    @Piinks
    Piinks
    on May 13, 2026
    Contributor

    Not sure if this is still reproducible, we should check.

  17. puneetkukreja98
    self-assigned this
    on May 14, 2026
  18. puneetkukreja98
    added a commit that references this issue on May 14, 2026

    test: Add test for Navigator pop type mismatches

    b68e861

  19. puneetkukreja98 commented on May 15, 2026

    @puneetkukreja98
    puneetkukreja98
    on May 15, 2026
    Contributor

    I have tested the issue and confirmed it still exists. In await showDialog<Null>(, the return type is set as Null, but a String is being returned instead Navigator.maybePop(context, "CANCEL"); . This type mismatch is what is causing the error.

  20. puneetkukreja98
    added 3 commits that reference this issue on May 15, 2026

    test: Add test for Navigator pop type mismatches

    762181d

    test: Add test for Navigator pop type mismatches

    8b997c7

    test: Add test for Navigator pop type mismatches

    74a47fd
  21. puneetkukreja98
    added 2 commits that reference this issue on May 29, 2026

    test: Add test for Navigator pop type mismatches

    7db4e28

    test: Add test for Navigator pop type mismatches

    99a79dc
  22. auto-submit
    closed this as completedin #186571on Jun 2, 2026
  23. victorsanni
    added a commit that references this issue on Jun 3, 2026

    Improve error message for type mismatch in Navigator.pop and maybePop. (

    40135be
  24. via-guy
    added a commit that references this issue on Jun 26, 2026

    Improve error message for type mismatch in Navigator.pop and maybePop. (

    d164579

  25. github-actions commented on Jul 14, 2026

    @github-actions
    github-actionsbot
    on Jul 14, 2026 – with GitHub Actions

    This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

  26. github-actions
    locked as resolved and limited conversation to collaborators on Jul 14, 2026
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P2Important issues not at the top of the work lista: error messageError messages from the Flutter frameworkc: crashStack traces logged to the consolef: routesNavigator, Router, and related APIs.found in release: 3.7Found to occur in 3.7found in release: 3.8Found to occur in 3.8frameworkflutter/packages/flutter repository. See also f: labels.has reproducible stepsThe issue has been confirmed reproducible and is ready to work onteam-frameworkOwned by Framework teamtriaged-frameworkTriaged by Framework team

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