问题
I am trying to create a simple layout in flutter but keep getting this error:
The following assertion was thrown building Text("Deliver features faster", textAlign: center): No Directionality widget found.
I think the problem may be in the TextDirection class property, but I have been unable to find it.
Here is my code:
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
void main(){
runApp( new MyHome());
}
class MyHome extends StatelessWidget{
@override
Widget build(BuildContext context) {
// TODO: implement build
return new Material(
child: new Container(
color: Colors.red,
margin: const EdgeInsets.all(5.0),
child: new Row(
children: <Widget>[
new Expanded(
child: new Text('Deliver features faster', textAlign: TextAlign.center),
),
new Expanded(
child: new Text('Craft beautiful UIs', textAlign: TextAlign.center),
),
new Expanded(
child: new FittedBox(
fit: BoxFit.contain, // otherwise the logo will be tiny
child: const FlutterLogo(),
),
),
],
)
),
);
}
}
Here is the full stack trace of the error:
The following assertion was thrown building Text("Deliver features faster", textAlign: center):
No Directionality widget found.
RichText widgets require a Directionality widget ancestor.
The specific widget that could not find a Directionality ancestor was:
RichText(textAlign: center, softWrap: wrapping at box width, maxLines: unlimited, text: "Deliver
features faster")
The ownership chain for the affected widget is:
RichText ← Text ← Expanded ← Row ← DecoratedBox ← Padding ← Container ← DefaultTextStyle ←
AnimatedDefaultTextStyle ← _InkFeatures-[GlobalKey#978b7 ink renderer] ← ⋯
Typically, the Directionality widget is introduced by the MaterialApp or WidgetsApp widget at the
top of your application widget tree. It determines the ambient reading direction and is used, for
example, to determine how to lay out text, how to interpret "start" and "end" values, and to resolve
EdgeInsetsDirectional, AlignmentDirectional, and other *Directional objects.
When the exception was thrown, this was the stack:
#0 debugCheckHasDirectionality.<anonymous closure> (package:flutter/src/widgets/debug.dart:223:7)
#1 debugCheckHasDirectionality (package:flutter/src/widgets/debug.dart:239:4)
#2 RichText.createRenderObject (package:flutter/src/widgets/basic.dart:4245:37)
#3 RenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4259:28)
#4 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#5 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#6 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#7 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#8 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#9 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#10 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#11 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#12 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#13 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#14 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#15 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#16 ParentDataElement.mount (package:flutter/src/widgets/framework.dart:3938:16)
#17 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#18 MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4738:32)
#19 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#20 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#21 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4633:14)
#22 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#23 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#24 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4633:14)
#25 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#26 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#27 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#28 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#29 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#30 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#31 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#32 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#33 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#34 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#35 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#36 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#37 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#38 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#39 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#40 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#41 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#42 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3752:22)
#43 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#44 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#45 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#46 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4633:14)
#47 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#48 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#49 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#50 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#51 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#52 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#53 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#54 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#55 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4633:14)
#56 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#57 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#58 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#59 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#60 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#61 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3752:22)
#62 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#63 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#64 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#65 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#66 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#67 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#68 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3752:22)
#69 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#70 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#71 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#72 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3636:16)
#73 Element.rebuild (package:flutter/src/widgets/framework.dart:3478:5)
#74 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3605:5)
#75 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3600:5)
#76 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2890:14)
#77 Element.updateChild (package:flutter/src/widgets/framework.dart:2693:12)
#78 RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:852:16)
#79 RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:823:5)
#80 RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:769:17)
#81 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2205:19)
#82 RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:768:13)
#83 BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding&WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:657:7)
#84 runApp (package:flutter/src/widgets/binding.dart:699:7)
#85 main (/data/user/0/com.yourcompany.flutterproject/cache/flutter_projectENWZDI/flutter_project/lib/main.dart:6:3)
#86 _startIsolate.<anonymous closure> (dart:isolate-patch/dart:isolate/isolate_patch.dart:279)
#87 _RawReceivePortImpl._handleMessage (dart:isolate-patch/dart:isolate/isolate_patch.dart:165)
════════════════════════════════════════════════════════════════════════════════════════════════════
Another exception was thrown: No Directionality widget found.
Another exception was thrown: Horizontal RenderFlex with multiple children has a null textDirection, so the layout order is undefined.
Another exception was thrown: 'package:flutter/src/rendering/box.dart': Failed assertion: line 1446 pos 12: 'hasSize': is not true.
uid=10079(com.yourcompany.flutterproject) Thread-5 identical 2 lines
Another exception was thrown: 'package:flutter/src/rendering/box.dart': Failed assertion: line 1446 pos 12: 'hasSize': is not true.
Another exception was thrown: 'package:flutter/src/rendering/proxy_box.dart': Failed assertion: line 1564 pos 12: 'hasSize': is not true.
回答1:
flutter doesn't know whether the text is LTR or RTL, so you need to tell him the textDirection explicitly
new Text("Hello", textDirection: TextDirection.ltr)
or you can just wrap the Text with a Directionality Widget
new Directionality(
textDirection: TextDirection.ltr,
child: new Text('Hello')
and the purpuse of that is :
A widget that determines the ambient directionality of text and text-direction-sensitive render objects.
And a Text widget in the scope of a MaterialApp widget does not need to be given an explicit writing direction because The default localization in the widgets and material libraries is LTR
回答2:
If you don't use MaterialApp you need to wrap your app into some widgets yourself
import 'dart:ui' as ui;
...
runApp(
new MediaQuery(
data: new MediaQueryData.fromWindow(ui.window),
child: new Directionality(
textDirection: TextDirection.rtl,
child: new MyHome())))
回答3:
The problem is not that you have not wrapped your widgets into MaterialApp. As the documentation says this error occurs due to the nesting of the same kind of Widgets like nesting of Row into Row, Column into Column or Column into ListView so the problem arises as it becomes unbounded constraints for the Widget so unable to identify the direction.
So to avoid this kind of problems usage of Flexible or Expanded occurs which identifies the remaining space.
In your case, you can simply give crossAxisAlignment with a value of start to the Row widget.
For more information, visit this documentation page
来源：https://stackoverflow.com/questions/49687181/no-directionality-widget-found