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Flutter setState () or markNeedsBuild () is called when the widget tree is locked

I'm having trouble finding the source of this exception, and the application is quite complex, so it’s hard to show any relevant piece of code. This is my repository at the time the error occurred: Github repo

I suspect the following code may be guilty:

Widget buildResultCard(Map result, BuildContext context) {
    String name = result["value"];
    String description =
        result["label"].replaceAll(new RegExp(r"<(?:.|\n)*?>"), "");
    TextEditingController controller = new TextEditingController(text: name);

    Function onPressed = () {
      showDialog(
          context: context,
          child: new AlertDialog(
            title: new Text("Name your schedule"),
            content: new TextField(
              autofocus: true,
              controller: controller,
            ),
            actions: <Widget>[
              new FlatButton(
                  onPressed: () {
                    String givenName = controller.text;
                    ScheduleMeta schedule = new ScheduleMeta(
                        givenName: givenName,
                        name: name,
                        type: _selectedChoice.value,
                        description: description);

                    scheduleStore
                        .dispatch(new AddScheduleAction(schedule: schedule));

                    scheduleStore.dispatch(
                        new SetCurrentScheduleAction(schedule: schedule));

                    fetchAllSchedules(scheduleStore.state.schedules)
                        .then((weeks) {
                      scheduleStore.dispatch(
                          new SetWeeksForCurrentScheduleAction(weeks: weeks));
                    });

                    Scaffold.of(context).showSnackBar(new SnackBar(
                          content: new Text("Added " + givenName),
                          action: new SnackBarAction(
                              label: "Undo",
                              onPressed: () {
                                scheduleStore.dispatch(
                                    new RemoveScheduleAction(schedule: name));

                                Scaffold.of(context).showSnackBar(new SnackBar(
                                      content: new Text(
                                          "Deleted " + givenName),
                                    ));
                              }),
                        ));

                    Navigator.of(context).pop();
                  },
                  child: new Text("Add")),
            ],
          ));
    };

    return new Card(
      child: new Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          new ListTile(
            leading: const Icon(Icons.schedule),
            title: new Text(name),
            subtitle: new Text(description),
            isThreeLine: true,
            dense: true,
          ),
          new ButtonTheme.bar(
            child: new ButtonBar(
              children: <Widget>[
                new FlatButton(
                    child: const Text('Add Schedule'),
                    onPressed: scheduleStore.state.schedules
                            .any((schedule) => schedule.name == name)
                        ? null
                        : onPressed)
              ],
            ),
          ),
        ],
      ),
    );
  }

An error appears when a dialog box is displayed, and when the user clicks a button in the dialog box, two Redux repository dispatches are sent directly one after another. The user interface behind the dialog subscribes to changes in the Redux repository.

, Dart/Flutter , , , setState() , .

, , ?

:

I/flutter (13466): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (13466): The following assertion was thrown while finalizing the widget tree:
I/flutter (13466): setState() or markNeedsBuild() called when widget tree was locked.
I/flutter (13466): This _ModalScope widget cannot be marked as needing to build because the framework is locked.
I/flutter (13466): The widget on which setState() or markNeedsBuild() was called was:
I/flutter (13466):   _ModalScope([LabeledGlobalKey<_ModalScopeState>#cb4cc]; state: _ModalScopeState#d4c02())
I/flutter (13466): 
I/flutter (13466): When the exception was thrown, this was the stack:
I/flutter (13466): #0      Element.markNeedsBuild.<anonymous closure> (package:flutter/src/widgets/framework.dart:3250)
I/flutter (13466): #2      Element.markNeedsBuild (package:flutter/src/widgets/framework.dart:3226)
I/flutter (13466): #3      State.setState (package:flutter/src/widgets/framework.dart:1072)
I/flutter (13466): #4      _ModalScopeState._routeSetState (package:flutter/src/widgets/routes.dart:473)
I/flutter (13466): #5      ModalRoute.setState (package:flutter/src/widgets/routes.dart:552)
I/flutter (13466): #6      ModalRoute.changedInternalState (package:flutter/src/widgets/routes.dart:889)
I/flutter (13466): #7      TransitionRoute&&LocalHistoryRoute.removeLocalHistoryEntry (package:flutter/src/widgets/routes.dart:317)
I/flutter (13466): #8      LocalHistoryEntry.remove (package:flutter/src/widgets/routes.dart:267)
I/flutter (13466): #9      DrawerControllerState.dispose (package:flutter/src/material/drawer.dart:147)
I/flutter (13466): #10     StatefulElement.unmount (package:flutter/src/widgets/framework.dart:3550)
I/flutter (13466): #11     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1626)
I/flutter (13466): #12     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #13     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #14     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #15     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #16     MultiChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4421)
I/flutter (13466): #17     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #18     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #19     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #20     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #21     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #22     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #23     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #24     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #25     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4321)
I/flutter (13466): #26     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #27     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #28     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #29     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #30     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #31     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4321)
I/flutter (13466): #32     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #33     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #34     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #35     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #36     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #37     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #38     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #39     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #40     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #41     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #42     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #43     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #44     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #45     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1624)
I/flutter (13466): #46     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3427)
I/flutter (13466): #47     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1622)
I/flutter (13466): #48     _InactiveElements._unmountAll (package:flutter/src/widgets/framework.dart:1636)
I/flutter (13466): #49     BuildOwner.finalizeTree.<anonymous closure> (package:flutter/src/widgets/framework.dart:2228)
I/flutter (13466): #50     BuildOwner.lockState (package:flutter/src/widgets/framework.dart:2060)
I/flutter (13466): #51     BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2227)
I/flutter (13466): #52     BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:505)
I/flutter (13466): #53     BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:189)
I/flutter (13466): #54     BindingBase&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:688)
I/flutter (13466): #55     BindingBase&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:636)
I/flutter (13466): #56     _drawFrame (file:///b/build/slave/Linux_Engine/build/src/flutter/lib/ui/hooks.dart:70)
I/flutter (13466): (elided one frame from class _AssertionError)
I/flutter (13466): ════════════════════════════════════════════════════════════════════════════════════════════════════
+10
4

. , setState .

:

Widget build(BuildContext context) {
    setState(() { print("foo"); });
    return Container();
}

setState . , Navigator.pop(context) setState . , :

Widget build(BuildContext context) {
    Navigator.pop(context);
    return Container();
}

.

, , Navigator.pop(context) .

+14

, , .

Future.delayed(Duration.zero,() => setState(() {... })); setState , setState.

:

+3

, setState, WidgetsBinding.addPostFrameCallback:

WidgetsBinding.instance
        .addPostFrameCallback((_) => setState(() {}));

, , .

0

I ran into the same problem when creating a widget that I must do Navigator.popbefore returning the widget to build.

Let me call Remy Roussel 's code :

Widget build(BuildContext context) {
    Navigator.pop(context);
    return Container();
}

This code above may cause an error, but you can only pop up because it contextis in build, how to do it?

Widget build(BuildContext context) {
    if(datas != null) // check datas
    {
      SchedulerBinding.instance.addPostFrameCallback((_){ // make pop action to next cycle
        Navigator.of(context).pop(datas); /*...your datas*/
      });
    }
    return Container();
}

This method is a combination of others, but I'm not sure if this is the best practice, if there are any errors, please leave a comment to tell me!

0
source

Source: https://habr.com/ru/post/1682646/

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