使用列时如何在步进器中使用扩展
How to use Expanded in stepper when using columns
这是一个相关的堆栈溢出问题。
Flutter : Step widget can not hold Expanded
如果阅读@derek-lakin 的评论，就会得出结论，应该在步进器中使用一列，因为步进器是可滚动的。我正在做完全相同的事情，但是我面临一个问题，即列使文本小部件仅占用所需的 space，而不是整个屏幕宽度。如果我用 Material 小部件包裹文本小部件并应用高度或颜色，我会注意到这一点。
我尝试将扩展小部件包裹在我的小部件列中以解决此问题。但是，我收到渲染错误。
谁能告诉我，我怎样才能构建一个步进器，其中一个步骤由 Expanded(Column(children:List[Widgets])).
我可以只使用列构建一个步进器，但我正在考虑使用扩展来纠正列
中不合适的大小问题
stepWidget = Expanded(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: widgets, //List of my widgets
));
这会产生以下错误：
I/flutter (19635): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (19635): The following assertion was thrown building NotificationListener<KeepAliveNotification>:
I/flutter (19635): Incorrect use of ParentDataWidget.
I/flutter (19635): Expanded widgets must be placed directly inside Flex widgets.
I/flutter (19635): Expanded(no depth, flex: 2, dirty) has a Flex ancestor, but there are other widgets between them:
I/flutter (19635): - RepaintBoundary-[<0>]
I/flutter (19635): - IndexedSemantics(index: 0)
I/flutter (19635): - KeepAlive(keepAlive: false)
I/flutter (19635): - SliverList(delegate: SliverChildListDelegate#de272(estimated child count: 1))
I/flutter (19635): - SliverPadding(padding: EdgeInsets.zero)
I/flutter (19635): - ShrinkWrappingViewport(axisDirection: down, offset: ScrollPositionWithSingleContext#83fdf(offset:
I/flutter (19635): 0.0, range: null..null, viewport: null, ScrollableState, ClampingScrollPhysics,
I/flutter (19635): IdleScrollActivity#b00f3, ScrollDirection.idle))
I/flutter (19635): - IgnorePointer-[GlobalKey#88af5](ignoring: false, ignoringSemantics: false)
I/flutter (19635): - Semantics(container: false, properties: SemanticsProperties, label: null, value: null, hint: null,
I/flutter (19635): hintOverrides: null)
I/flutter (19635): - Listener(listeners: [down], behavior: opaque)
I/flutter (19635): - _GestureSemantics
I/flutter (19635): - _ScrollSemantics-[GlobalKey#81c78]
I/flutter (19635): - RepaintBoundary
I/flutter (19635): - CustomPaint
I/flutter (19635): - RepaintBoundary
I/flutter (19635): - Expanded(flex: 1) (this is a different Expanded than the one with the problem)
I/flutter (19635): These widgets cannot come between a Expanded and its Flex.
I/flutter (19635): The ownership chain for the parent of the offending Expanded was:
I/flutter (19635): RepaintBoundary-[<0>] ← IndexedSemantics ← NotificationListener<KeepAliveNotification> ← KeepAlive
I/flutter (19635): ← AutomaticKeepAlive ← SliverList ← MediaQuery ← SliverPadding ← ShrinkWrappingViewport ←
I/flutter (19635): _ScrollableScope ← ⋯
I/flutter (19635):
I/flutter (19635): When the exception was thrown, this was the stack:
I/flutter (19635): #0 ParentDataElement.mount.<anonymous closure> (package:flutter/src/widgets/framework.dart:4015:7)
I/flutter (19635): #1 ParentDataElement.mount (package:flutter/src/widgets/framework.dart:4024:6)
I/flutter (19635): #2 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #3 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #4 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4838:14)
I/flutter (19635): #5 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #6 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #7 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4838:14)
I/flutter (19635): #8 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #9 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #10 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3710:16)
I/flutter (19635): #11 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (19635): #12 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3679:5)
I/flutter (19635): #13 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3674:5)
I/flutter (19635): #14 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #15 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #16 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3710:16)
I/flutter (19635): #17 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (19635): #18 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3679:5)
I/flutter (19635): #19 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3674:5)
I/flutter (19635): #20 ParentDataElement.mount (package:flutter/src/widgets/framework.dart:4025:11)
I/flutter (19635): #21 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #22 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #23 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3710:16)
I/flutter (19635): #24 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (19635): #25 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3679:5)
I/flutter (19635): #26 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3826:11)
I/flutter (19635): #27 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3674:5)
I/flutter (19635): #28 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #29 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #30 SliverMultiBoxAdaptorElement.updateChild (package:flutter/src/widgets/sliver.dart:1012:36)
I/flutter (19635): #31 SliverMultiBoxAdaptorElement.createChild.<anonymous closure> (package:flutter/src/widgets/sliver.dart:997:20)
I/flutter (19635): #32 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2266:19)
I/flutter (19635): #33 SliverMultiBoxAdaptorElement.createChild (package:flutter/src/widgets/sliver.dart:990:11)
I/flutter (19635): #34 RenderSliverMultiBoxAdaptor._createOrObtainChild.<anonymous closure> (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:256:23)
I/flutter (19635): #35 RenderObject.invokeLayoutCallback.<anonymous closure> (package:flutter/src/rendering/object.dart:1730:58)
I/flutter (19635): #36 PipelineOwner._enableMutationsToDirtySubtrees (package:flutter/src/rendering/object.dart:799:15)
I/flutter (19635): #37 RenderObject.invokeLayoutCallback (package:flutter/src/rendering/object.dart:1730:13)
I/flutter (19635): #38 RenderSliverMultiBoxAdaptor._createOrObtainChild (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:245:5)
I/flutter (19635): #39 RenderSliverMultiBoxAdaptor.addInitialChild (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:323:5)
I/flutter (19635): #40 RenderSliverList.performLayout (package:flutter/src/rendering/sliver_list.dart:78:12)
I/flutter (19635): #41 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #42 RenderSliverPadding.performLayout (package:flutter/src/rendering/sliver_padding.dart:182:11)
I/flutter (19635): #43 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #44 RenderViewportBase.layoutChildSequence (package:flutter/src/rendering/viewport.dart:405:13)
I/flutter (19635): #45 RenderShrinkWrappingViewport._attemptLayout (package:flutter/src/rendering/viewport.dart:1645:12)
I/flutter (19635): #46 RenderShrinkWrappingViewport.performLayout (package:flutter/src/rendering/viewport.dart:1608:20)
I/flutter (19635): #47 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #48 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #49 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #50 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #51 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #52 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #53 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #54 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #55 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #56 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #57 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #58 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #59 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #60 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #61 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #62 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #63 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #64 RenderFlex.performLayout (package:flutter/src/rendering/flex.dart:798:17)
I/flutter (19635): #65 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #66 MultiChildLayoutDelegate.layoutChild (package:flutter/src/rendering/custom_layout.dart:142:11)
I/flutter (19635): #67 _ScaffoldLayout.performLayout (package:flutter/src/material/scaffold.dart:339:7)
I/flutter (19635): #68 MultiChildLayoutDelegate._callPerformLayout (package:flutter/src/rendering/custom_layout.dart:212:7)
I/flutter (19635): #69 RenderCustomMultiChildLayoutBox.performLayout (package:flutter/src/rendering/custom_layout.dart:356:14)
I/flutter (19635): #70 RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:1509:7)
I/flutter (19635): #71 PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:768:18)
I/flutter (19635): #72 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:281:19)
I/flutter (19635): #73 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:677:13)
I/flutter (19635): #74 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5)
I/flutter (19635): #75 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter (19635): #76 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter (19635): #77 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter (19635): #78 _invoke (dart:ui/hooks.dart:151:13)
I/flutter (19635): #79 _drawFrame (dart:ui/hooks.dart:140:3)
I/flutter (19635): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (19635): Another exception was thrown: 'package:flutter/src/rendering/sliver_multi_box_adaptor.dart': Failed assertion: line 217 pos 16: 'indexOf(child) > index': is not true.
I/flutter (19635): Another exception was thrown: 'package:flutter/src/rendering/sliver_multi_box_adaptor.dart': Failed assertion: line 217 pos 16: 'indexOf(child) > index': is not true.
I/flutter (19635): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 2270 pos 20: '_debugCurrentBuildTarget == context': is not true.
I/flutter (19635): Another exception was thrown: NoSuchMethodError: The getter 'scrollOffsetCorrection' was called on null.
I/flutter (19635): Another exception was thrown: NoSuchMethodError: The method 'debugAssertIsValid' was called on null.
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderShrinkWrappingViewport#44117 relayoutBoundary=up10 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderIgnorePointer#7c8dd relayoutBoundary=up9 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#f736b relayoutBoundary=up8 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderPointerListener#3760f relayoutBoundary=up7 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderSemanticsGestureHandler#860e2 relayoutBoundary=up6 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: _RenderScrollSemantics#b1734 relayoutBoundary=up5 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#d9292 relayoutBoundary=up4 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderCustomPaint#44461 relayoutBoundary=up3 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#4425c relayoutBoundary=up2 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderFlex#e5d03 relayoutBoundary=up1 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: NoSuchMethodError: The method '<=' was called on null.
根据错误：Expanded widgets must be placed directly inside Flex widgets.
为什么？
根据 docs:
An Expanded widget must be a descendant of a Row, Column, or Flex, and the path from the Expanded widget to its enclosing Row, Column, or Flex must contain only StatelessWidgets or StatefulWidgets (not other kinds of widgets, like RenderObjectWidgets).
您可以将 Expanded 小部件放入 Column 并将 Column 放入您的 Step 小部件，但您不能将 Expanded 直接放入您的Step 小部件的 content。
一旦您提供完整的代码来为您提供解决方案，我将更新我的答案。
到那时，您可以执行以下操作。
Container(
width: double.infinity, //To make it use as much space as it wants
height: whateverHeightYouWantTo,
child: Column(
children: <Widget>[
Expanded(child: Widget()) //You'll probably won't need Expanded by now.
]
)
)
这是一个相关的堆栈溢出问题。
Flutter : Step widget can not hold Expanded
如果阅读@derek-lakin 的评论，就会得出结论，应该在步进器中使用一列，因为步进器是可滚动的。我正在做完全相同的事情，但是我面临一个问题，即列使文本小部件仅占用所需的 space，而不是整个屏幕宽度。如果我用 Material 小部件包裹文本小部件并应用高度或颜色，我会注意到这一点。
我尝试将扩展小部件包裹在我的小部件列中以解决此问题。但是，我收到渲染错误。
谁能告诉我，我怎样才能构建一个步进器，其中一个步骤由 Expanded(Column(children:List[Widgets])).
我可以只使用列构建一个步进器，但我正在考虑使用扩展来纠正列
中不合适的大小问题stepWidget = Expanded(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: widgets, //List of my widgets
));
这会产生以下错误：
I/flutter (19635): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (19635): The following assertion was thrown building NotificationListener<KeepAliveNotification>:
I/flutter (19635): Incorrect use of ParentDataWidget.
I/flutter (19635): Expanded widgets must be placed directly inside Flex widgets.
I/flutter (19635): Expanded(no depth, flex: 2, dirty) has a Flex ancestor, but there are other widgets between them:
I/flutter (19635): - RepaintBoundary-[<0>]
I/flutter (19635): - IndexedSemantics(index: 0)
I/flutter (19635): - KeepAlive(keepAlive: false)
I/flutter (19635): - SliverList(delegate: SliverChildListDelegate#de272(estimated child count: 1))
I/flutter (19635): - SliverPadding(padding: EdgeInsets.zero)
I/flutter (19635): - ShrinkWrappingViewport(axisDirection: down, offset: ScrollPositionWithSingleContext#83fdf(offset:
I/flutter (19635): 0.0, range: null..null, viewport: null, ScrollableState, ClampingScrollPhysics,
I/flutter (19635): IdleScrollActivity#b00f3, ScrollDirection.idle))
I/flutter (19635): - IgnorePointer-[GlobalKey#88af5](ignoring: false, ignoringSemantics: false)
I/flutter (19635): - Semantics(container: false, properties: SemanticsProperties, label: null, value: null, hint: null,
I/flutter (19635): hintOverrides: null)
I/flutter (19635): - Listener(listeners: [down], behavior: opaque)
I/flutter (19635): - _GestureSemantics
I/flutter (19635): - _ScrollSemantics-[GlobalKey#81c78]
I/flutter (19635): - RepaintBoundary
I/flutter (19635): - CustomPaint
I/flutter (19635): - RepaintBoundary
I/flutter (19635): - Expanded(flex: 1) (this is a different Expanded than the one with the problem)
I/flutter (19635): These widgets cannot come between a Expanded and its Flex.
I/flutter (19635): The ownership chain for the parent of the offending Expanded was:
I/flutter (19635): RepaintBoundary-[<0>] ← IndexedSemantics ← NotificationListener<KeepAliveNotification> ← KeepAlive
I/flutter (19635): ← AutomaticKeepAlive ← SliverList ← MediaQuery ← SliverPadding ← ShrinkWrappingViewport ←
I/flutter (19635): _ScrollableScope ← ⋯
I/flutter (19635):
I/flutter (19635): When the exception was thrown, this was the stack:
I/flutter (19635): #0 ParentDataElement.mount.<anonymous closure> (package:flutter/src/widgets/framework.dart:4015:7)
I/flutter (19635): #1 ParentDataElement.mount (package:flutter/src/widgets/framework.dart:4024:6)
I/flutter (19635): #2 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #3 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #4 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4838:14)
I/flutter (19635): #5 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #6 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #7 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4838:14)
I/flutter (19635): #8 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #9 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #10 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3710:16)
I/flutter (19635): #11 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (19635): #12 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3679:5)
I/flutter (19635): #13 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3674:5)
I/flutter (19635): #14 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #15 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #16 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3710:16)
I/flutter (19635): #17 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (19635): #18 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3679:5)
I/flutter (19635): #19 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3674:5)
I/flutter (19635): #20 ParentDataElement.mount (package:flutter/src/widgets/framework.dart:4025:11)
I/flutter (19635): #21 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #22 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #23 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3710:16)
I/flutter (19635): #24 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (19635): #25 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3679:5)
I/flutter (19635): #26 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3826:11)
I/flutter (19635): #27 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3674:5)
I/flutter (19635): #28 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (19635): #29 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (19635): #30 SliverMultiBoxAdaptorElement.updateChild (package:flutter/src/widgets/sliver.dart:1012:36)
I/flutter (19635): #31 SliverMultiBoxAdaptorElement.createChild.<anonymous closure> (package:flutter/src/widgets/sliver.dart:997:20)
I/flutter (19635): #32 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2266:19)
I/flutter (19635): #33 SliverMultiBoxAdaptorElement.createChild (package:flutter/src/widgets/sliver.dart:990:11)
I/flutter (19635): #34 RenderSliverMultiBoxAdaptor._createOrObtainChild.<anonymous closure> (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:256:23)
I/flutter (19635): #35 RenderObject.invokeLayoutCallback.<anonymous closure> (package:flutter/src/rendering/object.dart:1730:58)
I/flutter (19635): #36 PipelineOwner._enableMutationsToDirtySubtrees (package:flutter/src/rendering/object.dart:799:15)
I/flutter (19635): #37 RenderObject.invokeLayoutCallback (package:flutter/src/rendering/object.dart:1730:13)
I/flutter (19635): #38 RenderSliverMultiBoxAdaptor._createOrObtainChild (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:245:5)
I/flutter (19635): #39 RenderSliverMultiBoxAdaptor.addInitialChild (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:323:5)
I/flutter (19635): #40 RenderSliverList.performLayout (package:flutter/src/rendering/sliver_list.dart:78:12)
I/flutter (19635): #41 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #42 RenderSliverPadding.performLayout (package:flutter/src/rendering/sliver_padding.dart:182:11)
I/flutter (19635): #43 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #44 RenderViewportBase.layoutChildSequence (package:flutter/src/rendering/viewport.dart:405:13)
I/flutter (19635): #45 RenderShrinkWrappingViewport._attemptLayout (package:flutter/src/rendering/viewport.dart:1645:12)
I/flutter (19635): #46 RenderShrinkWrappingViewport.performLayout (package:flutter/src/rendering/viewport.dart:1608:20)
I/flutter (19635): #47 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #48 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #49 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #50 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #51 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #52 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #53 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #54 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #55 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #56 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #57 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #58 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #59 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #60 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #61 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #62 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (19635): #63 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #64 RenderFlex.performLayout (package:flutter/src/rendering/flex.dart:798:17)
I/flutter (19635): #65 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (19635): #66 MultiChildLayoutDelegate.layoutChild (package:flutter/src/rendering/custom_layout.dart:142:11)
I/flutter (19635): #67 _ScaffoldLayout.performLayout (package:flutter/src/material/scaffold.dart:339:7)
I/flutter (19635): #68 MultiChildLayoutDelegate._callPerformLayout (package:flutter/src/rendering/custom_layout.dart:212:7)
I/flutter (19635): #69 RenderCustomMultiChildLayoutBox.performLayout (package:flutter/src/rendering/custom_layout.dart:356:14)
I/flutter (19635): #70 RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:1509:7)
I/flutter (19635): #71 PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:768:18)
I/flutter (19635): #72 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:281:19)
I/flutter (19635): #73 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:677:13)
I/flutter (19635): #74 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5)
I/flutter (19635): #75 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter (19635): #76 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter (19635): #77 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter (19635): #78 _invoke (dart:ui/hooks.dart:151:13)
I/flutter (19635): #79 _drawFrame (dart:ui/hooks.dart:140:3)
I/flutter (19635): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (19635): Another exception was thrown: 'package:flutter/src/rendering/sliver_multi_box_adaptor.dart': Failed assertion: line 217 pos 16: 'indexOf(child) > index': is not true.
I/flutter (19635): Another exception was thrown: 'package:flutter/src/rendering/sliver_multi_box_adaptor.dart': Failed assertion: line 217 pos 16: 'indexOf(child) > index': is not true.
I/flutter (19635): Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 2270 pos 20: '_debugCurrentBuildTarget == context': is not true.
I/flutter (19635): Another exception was thrown: NoSuchMethodError: The getter 'scrollOffsetCorrection' was called on null.
I/flutter (19635): Another exception was thrown: NoSuchMethodError: The method 'debugAssertIsValid' was called on null.
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderShrinkWrappingViewport#44117 relayoutBoundary=up10 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderIgnorePointer#7c8dd relayoutBoundary=up9 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#f736b relayoutBoundary=up8 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderPointerListener#3760f relayoutBoundary=up7 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderSemanticsGestureHandler#860e2 relayoutBoundary=up6 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: _RenderScrollSemantics#b1734 relayoutBoundary=up5 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#d9292 relayoutBoundary=up4 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderCustomPaint#44461 relayoutBoundary=up3 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#4425c relayoutBoundary=up2 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: RenderBox was not laid out: RenderFlex#e5d03 relayoutBoundary=up1 NEEDS-PAINT
I/flutter (19635): Another exception was thrown: NoSuchMethodError: The method '<=' was called on null.
根据错误：Expanded widgets must be placed directly inside Flex widgets.
为什么？ 根据 docs:
An Expanded widget must be a descendant of a Row, Column, or Flex, and the path from the Expanded widget to its enclosing Row, Column, or Flex must contain only StatelessWidgets or StatefulWidgets (not other kinds of widgets, like RenderObjectWidgets).
您可以将 Expanded 小部件放入 Column 并将 Column 放入您的 Step 小部件，但您不能将 Expanded 直接放入您的Step 小部件的 content。
一旦您提供完整的代码来为您提供解决方案，我将更新我的答案。
到那时，您可以执行以下操作。
Container(
width: double.infinity, //To make it use as much space as it wants
height: whateverHeightYouWantTo,
child: Column(
children: <Widget>[
Expanded(child: Widget()) //You'll probably won't need Expanded by now.
]
)
)