flutter 未找到方向性构件

wxclj1h5  于 2023-10-22  发布在  Flutter
关注(0)|答案(4)|浏览(104)

我试图在flutter中创建一个简单的布局，但不断得到这个错误：
构建Text时抛出了以下Assert（“Deliver features faster”，textAlign：center）：未找到方向性构件。
我想问题可能出在TextDirection类属性上，但我一直找不到它。
下面是我的代码：

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(),
              ),
            ),
          ],
        )
      ),
    );
  }
}

下面是错误的完整堆栈跟踪：

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.
flutter

4条答案

按热度按时间
5lhxktic

5lhxktic1#

flutter不知道文本是LTR还是RTL，因此您需要显式地告诉他textDirection

Text("Hello", textDirection: TextDirection.ltr)

或者你可以用一个Directionality小部件 Package 文本

Directionality(
          textDirection: TextDirection.ltr,
          child: Text('Hello')

其目的是：
确定文本和文本方向敏感呈现对象的环境方向性的小部件。
MaterialApp小部件范围内的Text小部件不需要明确的编写方向，因为小部件和材质库中的默认本地化是LTR

赞(0）分享  回复(0）举报  2023-10-22
vatpfxk5

vatpfxk52#

如果您不使用MaterialApp，则需要自己将应用程序 Package 到一些小部件中

import 'dart:ui' as ui;
...
runApp(
    new MediaQuery(
        data: new MediaQueryData.fromWindow(ui.window),
        child: new Directionality(
            textDirection: TextDirection.rtl,
            child: new MyHome())))
赞(0）分享  回复(0）举报  2023-10-22
gwbalxhn

gwbalxhn3#

如果您没有在树层次结构的根级别使用MaterialApp或WidgetsApp，则会出现此错误。

解决方案：

void main() {
  runApp(
    MaterialApp(home: MyHome()), // use MaterialApp
  );
}

class MyHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold( // use Scaffold also in order to provide material app widgets
      body: Center(child: Text("Something")),
    );
  }
}
赞(0）分享  回复(0）举报  2023-10-22
zrfyljdw

zrfyljdw4#

问题不在于您没有将小部件 Package 到MaterialApp中。正如文档中所说，发生此错误是由于嵌套相同类型的Widget，如嵌套行到行，列到列或列到ListView中，因此问题出现了，因为它成为Widget的无限约束，因此无法识别方向。
因此，为了避免这种问题，使用Flexible或Expanded来标识剩余空间。
在本例中，您可以简单地将值为start的crossAxisAlignment给予给Row小部件。
有关更多信息，请访问此documentation页面

赞(0）分享  回复(0）举报  2023-10-22
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