No Directionality widget found. RichText widgets require a Directionality widget a Directio.......

• 报错
  flutter: No Directionality widget found.
  flutter: RichText widgets require a Directionality widget ancestor.
  flutter: The specific widget that could not find a Directionality ancestor was:
  flutter: RichText
  
• 使用text组件时，没有设置文字对齐方式，导致的报错，一般情况下App的最外层都是Scaffold组件包裹，因此Text有默认的样式，如果Text组件的父组件没有Scaffold，需要设置样式。
• 解决：textDirection: TextDirection.ltr

import 'package:flutter/material.dart';void main()=> runApp(MyApp());class MyApp extends StatelessWidget {@override// build 返回一个Widget 一个类就是widgetWidget build(BuildContext context) {return Container(child: Text('123',textDirection: TextDirection.ltr),);}
}