Exception on build if constraints changed.

[jonl-percsolutions-com]

What is the bug?

An exception can occur in MapInteractiveViewer.onMapStateChange if the constraints changed during a rebuild. We have seen this in 8.1.1 - 8.2.2.

The following assertion was thrown while dispatching notifications for MapControllerImpl:
setState() or markNeedsBuild() called during build.

This MapInteractiveViewer 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: MapInteractiveViewer
  dependencies: [MediaQuery]
  state: MapInteractiveViewerState#aa93f(tickers: tracking 18 tickers)
The widget which was currently being built when the offending call was made was: LayoutBuilder
  renderObject: _RenderLayoutBuilder#d5341 relayoutBoundary=up9 NEEDS-LAYOUT NEEDS-PAINT
When the exception was thrown, this was the stack: 
#0      Element.markNeedsBuild.<anonymous closure> (package:flutter/src/widgets/framework.dart:5289:9)
#1      Element.markNeedsBuild (package:flutter/src/widgets/framework.dart:5301:6)
#2      State.setState (package:flutter/src/widgets/framework.dart:1227:15)
#3      MapInteractiveViewerState.onMapStateChange (package:flutter_map/src/gestures/map_interactive_viewer.dart:182:5)
#4      ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:439:24)
#5      ValueNotifier.value= (package:flutter/src/foundation/change_notifier.dart:564:5)
#6      MapControllerImpl.value= (package:flutter_map/src/map/controller/map_controller_impl.dart:81:49)
#7      MapControllerImpl.setNonRotatedSizeWithoutEmittingEvent (package:flutter_map/src/map/controller/map_controller_impl.dart:321:7)
#8      _FlutterMapStateContainer._updateAndEmitSizeIfConstraintsChanged (package:flutter_map/src/map/widget.dart:135:24)
#9      _FlutterMapStateContainer.build.<anonymous closure> (package:flutter_map/src/map/widget.dart:98:11)
#10     _LayoutBuilderElement._rebuildWithConstraints.updateChildCallback (package:flutter/src/widgets/layout_builder.dart:201:77)
#11     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:3056:19)
#12     _LayoutBuilderElement._rebuildWithConstraints (package:flutter/src/widgets/layout_builder.dart:240:12)
#13     RenderObject.invokeLayoutCallback.<anonymous closure> (package:flutter/src/rendering/object.dart:2827:17)
#14     PipelineOwner._enableMutationsToDirtySubtrees (package:flutter/src/rendering/object.dart:1161:15)
#15     RenderObject.invokeLayoutCallback (package:flutter/src/rendering/object.dart:2826:14)
#16     RenderConstrainedLayoutBuilder.rebuildIfNecessary (package:flutter/src/widgets/layout_builder.dart:293:5)
#17     _RenderLayoutBuilder.performLayout (package:flutter/src/widgets/layout_builder.dart:390:5)
#18     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#19     RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:115:18)
#20     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#21     RenderPadding.performLayout (package:flutter/src/rendering/shifted_box.dart:243:12)
#22     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#23     RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:115:18)
#24     _RenderCustomClip.performLayout (package:flutter/src/rendering/proxy_box.dart:1483:11)
#25     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#26     RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:115:18)
#27     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#28     ChildLayoutHelper.layoutChild (package:flutter/src/rendering/layout_helper.dart:62:11)
#29     RenderStack._computeSize (package:flutter/src/rendering/stack.dart:646:43)
#30     RenderStack.performLayout (package:flutter/src/rendering/stack.dart:673:12)
#31     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#32     RenderConstrainedBox.performLayout (package:flutter/src/rendering/proxy_box.dart:293:14)
#33     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#34     RenderPadding.performLayout (package:flutter/src/rendering/shifted_box.dart:243:12)
#35     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#36     RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:115:18)
#37     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#38     ChildLayoutHelper.layoutChild (package:flutter/src/rendering/layout_helper.dart:62:11)
#39     RenderFlex._computeSizes (package:flutter/src/rendering/flex.dart:1161:28)
#40     RenderFlex.performLayout (package:flutter/src/rendering/flex.dart:1255:32)
#41     RenderObject.layout (package:flutter/src/rendering/object.dart:2715:7)
#42     _RenderLayoutBuilder.performLayout (package:flutter/src/widgets/layout_builder.dart:392:14)
#43     RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:2548:7)
#44     PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:1112:18)
#45     PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:1125:15)
#46     RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:616:23)
#47     WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:1231:13)
#48     RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:482:5)
#49     SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1442:15)
#50     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1355:9)
#51     SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:1208:5)
#52     _invoke (dart:ui/hooks.dart:316:13)
#53     PlatformDispatcher._drawFrame (dart:ui/platform_dispatcher.dart:428:5)
#54     _drawFrame (dart:ui/hooks.dart:288:31)

How can we reproduce it?

It is intermittent to reproduce, but the exception is clear.

If _FlutterMapStateContainer._updateAndEmitSizeIfConstraintsChanged actually detects a change, and the MapInteractiveViewer.onMapStateChange is attached as a listener, then this will cause a "setState" call to be invoked during the build process.

Do you have a potential solution?

Best solution is likely to modify the behavior of _FlutterMapStateContainer._updateAndEmitSizeIfConstraintsChanged` so the whole check occurs in a postFrameCallback

May also need to modify the behavior MapInteractiveViewerState.onMapStateChange so that setState is called within a post frame callback.

[jonl-percsolutions-com]

My interim solution until this is resolved. not sure what other issues may arise from this.

class _MyMapControllerImpl extends MapControllerImpl {

  bool _initialChangeRotateDone = false;

  @override
  bool setNonRotatedSizeWithoutEmittingEvent(Size nonRotatedSize) {
    if (!_initialChangeRotateDone) {
      _initialChangeRotateDone = true;
      return super.setNonRotatedSizeWithoutEmittingEvent(nonRotatedSize);
    }
    if (nonRotatedSize != MapCamera.kImpossibleSize &&
        nonRotatedSize != camera.nonRotatedSize) {
      WidgetsBinding.instance.addPostFrameCallback((_) {
        super.setNonRotatedSizeWithoutEmittingEvent(nonRotatedSize);
      },);

      return true;
    }

    return false;
  }

}

[JaffaKetchup]

Hey @jonl-percsolutions-com ,

Thanks for the report. That workaround does look like something that we could implement. However we need to be 100% sure how the issue exists first so we can test repeatedly whether it remains fixed. Is there any way you could make a small MRE which at least triggers the issue most of the time?

[jonl-percsolutions-com]

@JaffaKetchup,

This is an intermittent issue..

All you have to do to confirm the possible issue is trace the log. If MapInteractiveViewerState.onMapStateChange is called during a build process, there will be an exception because it calls setState(), and set state shouldn't be called during a build process. I think newer versions of flutter are supposedly handling these a bit better I am using flutter 3.29.1 currently, which maybe if you run with that it will be more re-producible.

This is the offending line of code in MapInteractiveViewerState

  /// Rebuilds the map widget
  void onMapStateChange() {
    _updateKeyboardPanAnimationZoomLevel();
    setState(() {});
  }

[JaffaKetchup]

Could you please explain how you are "changing the constraints during a rebuild"? I can see that there might be a bug, but I need to reproduce it to prove that any fix has worked.