Flutter: type 'Future' is not a subtype of type 'Widget' // MaterialPageRoute(null))

Question

I am trying to navigate to the camera screen and when I trigger the navigation, I get the error

Another exception was thrown: type 'Future<dynamic>' is not a subtype of type 'Widget'
Another exception was thrown: setState() or markNeedsBuild() called during build.

The error points to the navigation from previous page I came from.

I also saw this error in there too

The AnimationController notifying status listeners was: AnimationController#a911e(⏮ 0.000; paused; for MaterialPageRoute<dynamic>(null))

onTap: () => Navigator.push(
   context,
  MaterialPageRoute(
    builder: (context) => CameraScreen())),

This is the function that gets the error

captureImageWithCamera() async {
    Navigator.pop(this.context);
    File imageFile = await ImagePicker.pickImage(
      source: ImageSource.camera,
      maxHeight: 680,
      maxWidth: 970,
    );
    if (imageFile != null) {
      //imageFile = await cropImage(imageFile);
      setState(() {
        //this.file = imageFile as File;
        print(file);
      });
      await controller.dispose();
    }
  }

Just for full context, here's the full builder from the first page that calls the navigation to the camera screen. You'll see the navigation to the CameraScreen in there.

createStoryView() {
    return FutureBuilder(
      future: usersReference.document(currentOnlineUserId).get(),
      builder: (context, dataSnapshot) {
        if (!dataSnapshot.hasData) {
          return circularProgress();
        } else {
          User user = User.fromDocument(dataSnapshot.data);
          return Material(
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                Padding(
                  padding: const EdgeInsets.all(0.0),
                  child: Card(
                    color: Colors.white,
                    elevation: 0.0,
                    child: Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: ListTile(
                        leading: Stack(
                          children: <Widget>[
                            GestureDetector(
                              child: Padding(
                                padding: EdgeInsets.only(top: 0.0, bottom: 0.0),
                                child: user.photoUrl.isNotEmpty
                                    ? CircleAvatar(
                                        radius: 30.0,
                                        backgroundColor: Colors.grey,
                                        backgroundImage:
                                            CachedNetworkImageProvider(
                                                user.photoUrl),
                                      )
                                    : CircleAvatar(
                                        radius: 30.0,
                                        backgroundColor: Colors.grey,
                                      ),
                              ),
                              onTap: () => Navigator.push(
                                  context,
                                  MaterialPageRoute(
                                      builder: (context) => StoryPageView())),
                            ),
                          ],
                        ),
                        title: Text(
                          user.profileName,
                          style: TextStyle(fontWeight: FontWeight.bold),
                        ),
                        subtitle: Text("Add a Story"),
                        onTap: () => Navigator.push(
                            context,
                            MaterialPageRoute(
                                builder: (context) => CameraScreen())),
                      ),
                    ),
                  ),
                ),
                Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: Text(
                    "Viewed Stories",
                    style: TextStyle(
                      color: Colors.grey,
                      fontWeight: FontWeight.bold,
                    ),
                  ),
                ),
                Expanded(
                  child: Container(
                    padding: const EdgeInsets.all(0.0),
                    color: Colors.white,
                    child: ListView(
                      children: <Widget>[
                        Padding(
                          padding: const EdgeInsets.all(8.0),
                          child: ListTile(
                            leading: CircleAvatar(
                              radius: 30.0,
                              backgroundColor: Colors.grey,
                            ),
                            title: Text(
                              "Username",
                              style: TextStyle(
                                fontWeight: FontWeight.bold,
                              ),
                            ),
                            subtitle: Text("Timestamp"),
                            onTap: () => Navigator.push(
                                context,
                                MaterialPageRoute(
                                    builder: (context) => StoryPageView())),
                          ),
                        ),
                      ],
                    ),
                  ),
                ),
              ],
            ),
          );
        }
      },
    );
  }

Here is the builder for the CameraPage

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.white,
        iconTheme: IconThemeData(color: Colors.blue),
        title: Text(
          "Story Post",
          style: TextStyle(
            color: Colors.blue,
            fontSize: 22.0,
          ),
        ),
      ),
      body: file == null ? captureImageWithCamera() : displayStoryUploadScreen(),
    );
  }

Here's the full error message

══╡ EXCEPTION CAUGHT BY ANIMATION LIBRARY ╞═════════════════════════════════════════════════════════
The following assertion was thrown while notifying status listeners for AnimationController:
setState() or markNeedsBuild() called during build.
This _ModalScope<dynamic> widget cannot be marked as needing to build because the framework is
already in the process of building widgets.  A widget can be marked as needing to be built during
the build phase only if one of its ancestors is currently building. This exception is allowed
because the framework builds parent widgets before children, which means a dirty descendant will
always be built. Otherwise, the framework might not visit this widget during this build phase.
The widget on which setState() or markNeedsBuild() was called was:
  _ModalScope<dynamic>-[LabeledGlobalKey<_ModalScopeState<dynamic>>#0c8ee]
The widget which was currently being built when the offending call was made was:
  CameraScreen
When the exception was thrown, this was the stack:
[38;5;244m#0      Element.markNeedsBuild.<anonymous closure>[39;49m
[38;5;244m#1      Element.markNeedsBuild[39;49m
[38;5;244m#2      State.setState[39;49m
[38;5;244m#3      _ModalScopeState._routeSetState[39;49m
[38;5;244m#4      ModalRoute.setState[39;49m
[38;5;244m#5      ModalRoute.changedInternalState[39;49m
[38;5;244m#6      TransitionRoute._handleStatusChanged[39;49m
[38;5;244m#7      AnimationLocalStatusListenersMixin.notifyStatusListeners[39;49m
[38;5;244m#8      AnimationController._checkStatusChanged[39;49m
[38;5;244m#9      AnimationController._animateToInternal[39;49m
[38;5;244m#10     AnimationController.reverse[39;49m
[38;5;244m#11     TransitionRoute.didPop[39;49m
[38;5;244m#12     LocalHistoryRoute.didPop[39;49m
[38;5;244m#13     _RouteEntry.pop[39;49m
[38;5;244m#14     NavigatorState.pop[39;49m
[38;5;244m#15     Navigator.pop[39;49m
[38;5;248m#16     _CameraScreenState.captureImageWithCamera[39;49m
[38;5;248m#17     _CameraScreenState.build[39;49m
[38;5;244m#18     StatefulElement.build[39;49m
[38;5;244m#19     ComponentElement.performRebuild[39;49m
[38;5;244m#20     StatefulElement.performRebuild[39;49m
[38;5;244m#21     Element.rebuild[39;49m
[38;5;244m#22     ComponentElement._firstBuild[39;49m
[38;5;244m#23     StatefulElement._firstBuild[39;49m
[38;5;244m#24     ComponentElement.mount[39;49m
...     Normal element mounting (24 frames)
[38;5;244m#48     Element.inflateWidget[39;49m
[38;5;244m#49     MultiChildRenderObjectElement.mount[39;49m
...     Normal element mounting (136 frames)
[38;5;244m#185    Element.inflateWidget[39;49m
[38;5;244m#186    Element.updateChild[39;49m
[38;5;244m#187    RenderObjectElement.updateChildren[39;49m
[38;5;244m#188    MultiChildRenderObjectElement.update[39;49m
[38;5;244m#189    Element.updateChild[39;49m
[38;5;244m#190    ComponentElement.performRebuild[39;49m
[38;5;244m#191    StatefulElement.performRebuild[39;49m
[38;5;244m#192    Element.rebuild[39;49m
[38;5;244m#193    StatefulElement.update[39;49m
[38;5;244m#194    Element.updateChild[39;49m
[38;5;244m#195    ComponentElement.performRebuild[39;49m
[38;5;244m#196    Element.rebuild[39;49m
[38;5;244m#197    ProxyElement.update[39;49m
[38;5;244m#198    _InheritedNotifierElement.update[39;49m
[38;5;244m#199    Element.updateChild[39;49m
[38;5;244m#200    SingleChildRenderObjectElement.update[39;49m
[38;5;244m#201    Element.updateChild[39;49m
[38;5;244m#202    ComponentElement.performRebuild[39;49m
[38;5;244m#203    StatefulElement.performRebuild[39;49m
[38;5;244m#204    Element.rebuild[39;49m
[38;5;244m#205    StatefulElement.update[39;49m
[38;5;244m#206    Element.updateChild[39;49m
[38;5;244m#207    SingleChildRenderObjectElement.update[39;49m
[38;5;244m#208    Element.updateChild[39;49m
[38;5;244m#209    SingleChildRenderObjectElement.update[39;49m
[38;5;244m#210    Element.updateChild[39;49m
[38;5;244m#211    ComponentElement.performRebuild[39;49m
[38;5;244m#212    Element.rebuild[39;49m
[38;5;244m#213    StatelessElement.update[39;49m
[38;5;244m#214    Element.updateChild[39;49m
[38;5;244m#215    ComponentElement.performRebuild[39;49m
[38;5;244m#216    Element.rebuild[39;49m
[38;5;244m#217    ProxyElement.update[39;49m
[38;5;244m#218    Element.updateChild[39;49m
[38;5;244m#219    ComponentElement.performRebuild[39;49m
[38;5;244m#220    StatefulElement.performRebuild[39;49m
[38;5;244m#221    Element.rebuild[39;49m
[38;5;244m#222    BuildOwner.buildScope[39;49m
[38;5;244m#223    WidgetsBinding.drawFrame[39;49m
[38;5;244m#224    RendererBinding._handlePersistentFrameCallback[39;49m
[38;5;244m#225    SchedulerBinding._invokeFrameCallback[39;49m
[38;5;244m#226    SchedulerBinding.handleDrawFrame[39;49m
[38;5;244m#227    SchedulerBinding._handleDrawFrame[39;49m
[38;5;244m#231    _invoke  (dart:ui/hooks.dart:253:10)[39;49m
[38;5;244m#232    _drawFrame  (dart:ui/hooks.dart:211:3)[39;49m
(elided 3 frames from dart:async)
The AnimationController notifying status listeners was:
  AnimationController#ac0aa(⏮ 0.000; paused; for MaterialPageRoute<dynamic>(null))
════════════════════════════════════════════════════════════════════════════════════════════════════

[38;5;248m════════ Exception caught by animation library ═════════════════════════════════[39;49m
[38;5;244mThe following assertion was thrown while notifying status listeners for AnimationController:[39;49m
setState() or markNeedsBuild() called during build.

[38;5;244mThis _ModalScope<dynamic> widget cannot be marked as needing to build because the framework is already in the process of building widgets.  A widget can be marked as needing to be built during the build phase only if one of its ancestors is currently building. This exception is allowed because the framework builds parent widgets before children, which means a dirty descendant will always be built. Otherwise, the framework might not visit this widget during this build phase.[39;49m
[38;5;244mThe widget on which setState() or markNeedsBuild() was called was: _ModalScope<dynamic>-[LabeledGlobalKey<_ModalScopeState<dynamic>>#0c8ee][39;49m
    [38;5;244mstate: _ModalScopeState<dynamic>#b0964[39;49m
[38;5;244mThe widget which was currently being built when the offending call was made was: CameraScreen[39;49m
    [38;5;244mdirty[39;49m
    [38;5;244mstate: _CameraScreenState#54b04[39;49m
[38;5;244mWhen the exception was thrown, this was the stack[39;49m
[38;5;244m#0      Element.markNeedsBuild.<anonymous closure>[39;49m
[38;5;244m#1      Element.markNeedsBuild[39;49m
[38;5;244m#2      State.setState[39;49m
[38;5;244m#3      _ModalScopeState._routeSetState[39;49m
[38;5;244m#4      ModalRoute.setState[39;49m
[38;5;244m...[39;49m
[38;5;244mThe AnimationController notifying status listeners was: AnimationController#ac0aa(⏮ 0.000; paused; for MaterialPageRoute<dynamic>(null))[39;49m
[38;5;248m════════════════════════════════════════════════════════════════════════════════[39;49m
Another exception was thrown: type 'Future<dynamic>' is not a subtype of type 'Widget'

[38;5;248m════════ Exception caught by widgets library ═══════════════════════════════════[39;49m
type 'Future<dynamic>' is not a subtype of type 'Widget'
[38;5;244mThe relevant error-causing widget was[39;49m
    [38;5;248mCameraScreen[39;49m
[38;5;248m════════════════════════════════════════════════════════════════════════════════[39;49m

Please post the full error code. It usually includes information of where the error is happening — lenz, Sep 10 '20 at 21:05

Emil Tejeda · Answer 1 · 2020-09-10T20:55:52.393

1

The builder function for MaterialPageRoute should return an Widget or class the implnentes from StatelessWidget or StatefullWidget, apparently CameraScreen is neither of those.

Your captureImageWithCamera does will return a Future<void> but the body of scaffold must be a widget, also is not clear what is the return type for displayStoryUploadScreen but also must be a widget.

if you need the value of a future to build your widget you'll need to use FutureBuilder to await it without looking the render tree.

edited Sep 10 '20 at 20:55

answered Sep 10 '20 at 20:32

Emil Tejeda

36
1
3

I added the Widget that implements the Camera Screen. I didn't want to add the whole page because there's a lot in there. Let me know if I missed anything @Emil – Indigo Sep 10 '20 at 20:45

Flutter: type 'Future' is not a subtype of type 'Widget' // MaterialPageRoute(null))

1 Answers1