No Directionality widget found

最新推荐文章于 2024-04-10 21:20:56 发布

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最新推荐文章于 2024-04-10 21:20:56 发布

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文章标签： ui 移动开发

原文链接：http://www.cnblogs.com/pythonClub/p/10569699.html

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博客指出在Flutter开发中，因相同类型的Widget嵌套，如Row嵌套Row、Column嵌套Column等，会产生无界约束问题，导致无法确定方向。为避免此类问题，可使用Flexible或Expanded来识别剩余空间。

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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.

用 materialapp:

import 'package:flutter/material.dart';
import 'dart:ui' as ui;
void main() {
  runApp(new MyApp());
}


class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return MaterialApp(
      title: 'hello',
      home: Container(
        color: Colors.red,
        child: Column(
          children: <Widget>[
            RaisedButton(
              child: Text('just test', textDirection: TextDirection.ltr,),
            )
          ],
        ),
      ),
    );
  }
}

不用materialapp

import 'package:flutter/material.dart';
import 'dart:ui' as ui;
void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return MediaQuery(
      data: MediaQueryData.fromWindow(ui.window),
      child: Directionality(textDirection: TextDirection.rtl, child: Container(
        color: Colors.grey,
        child: Column(
          children: <Widget>[
            RaisedButton(
              child: Text('just test', textDirection: TextDirection.ltr,),
            )
          ],
        ),
      )),
    );
  }
}

转载于:https://www.cnblogs.com/pythonClub/p/10569699.html