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问没有找到MaterialLocalizations - MyApp小部件需要由本地化小部件祖先提供MaterialLocalizations
EN

Stack Overflow用户

提问于 2019-05-23 04:47:45

回答 10查看 53.7K关注 0票数 34

我只是想用按钮创建一个应用程序，当按下按钮时，它会显示一个警告信息。

但是它给了我这个错误(下面提到)。

我参考这视频编写了这段代码。

我使用adb连接在android手机上运行这个应用程序。

请救救..！

代码

import 'package:flutter/material.dart';

void main(){
  runApp(MyApp());
}

class MyApp extends StatelessWidget{
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Test",
      home: Scaffold(
        appBar: AppBar(title: Text("Test")),
        body: Container(
          child: Center(
            child: RaisedButton(
              color: Colors.redAccent,
              textColor: Colors.white,
              onPressed: (){testAlert(context);},
              child: Text("PressMe"),
            ),
          ),
        ),
      ),
    );
  }
  void testAlert(BuildContext context){
    var alert = AlertDialog(
      title: Text("Test"),
      content: Text("Done..!"),
    );

    showDialog(
        context: context,
        builder: (BuildContext context){
          return alert;
        }
    );
  }
}

这就是我写的代码。我还尝试将testAlert()函数的内容直接插入到onPressed中，但不起作用。

错误

Performing hot reload...
Syncing files to device ZUK Z2131...
Reloaded 0 of 419 libraries in 1,929ms.
I/flutter (18652): ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
I/flutter (18652): The following assertion was thrown while handling a gesture:
I/flutter (18652): No MaterialLocalizations found.
I/flutter (18652): MyApp widgets require MaterialLocalizations to be provided by a Localizations widget ancestor.
I/flutter (18652): Localizations are used to generate many different messages, labels,and abbreviations which are used
I/flutter (18652): by the material library. 
I/flutter (18652): To introduce a MaterialLocalizations, either use a  MaterialApp at the root of your application to
I/flutter (18652): include them automatically, or add a Localization widget with a MaterialLocalizations delegate.
I/flutter (18652): The specific widget that could not find a MaterialLocalizations ancestor was:
I/flutter (18652):   MyApp
I/flutter (18652): The ancestors of this widget were:
I/flutter (18652):   [root]
I/flutter (18652): 
I/flutter (18652): When the exception was thrown, this was the stack:
I/flutter (18652): #0      debugCheckHasMaterialLocalizations.<anonymous closure> (package:flutter/src/material/debug.dart:124:7)
I/flutter (18652): #1      debugCheckHasMaterialLocalizations (package:flutter/src/material/debug.dart:127:4)
I/flutter (18652): #2      showDialog (package:flutter/src/material/dialog.dart:635:10)
I/flutter (18652): #3      MyApp.testAlert (package:flutter_app/main.dart:33:5)
I/flutter (18652): #4      MyApp.build.<anonymous closure> (package:flutter_app/main.dart:19:29)
I/flutter (18652): #5      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:507:14)
I/flutter (18652): #6      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:562:30)
I/flutter (18652): #7      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:102:24)
I/flutter (18652): #8      TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:242:9)
I/flutter (18652): #9      TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:175:7)
I/flutter (18652): #10     PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:315:9)
I/flutter (18652): #11     PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:73:12)
I/flutter (18652): #12     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:11)
I/flutter (18652): #13     _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:180:19)
I/flutter (18652): #14     _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:158:22)
I/flutter (18652): #15     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:138:7)
I/flutter (18652): #16     _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:101:7)
I/flutter (18652): #17     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:85:7)
I/flutter (18652): #18     _invoke1 (dart:ui/hooks.dart:168:13)
I/flutter (18652): #19     _dispatchPointerDataPacket (dart:ui/hooks.dart:122:5)
I/flutter (18652): 
I/flutter (18652): Handler: onTap
I/flutter (18652): Recognizer:
I/flutter (18652):   TapGestureRecognizer#d5d82(debugOwner: GestureDetector, state: possible, won arena, finalPosition:
I/flutter (18652):   Offset(220.2, 406.1), sent tap down)
I/flutter (18652): ════════════════════════════════════════════════════════════════════════════════════════════════════
W/ActivityThread(18652): handleWindowVisibility: no activity for token android.os.BinderProxy@59b4e8d
I/ViewRootImpl(18652): CPU Rendering VSync enable = true

android

dart

flutter

回答 10

Stack Overflow用户

回答已采纳

发布于 2019-05-23 05:02:03

这是因为您要传递给showDialog方法的上下文是一个在小部件树中还没有MaterialLocalizations小部件的context，MaterialLocalizations小部件是由MaterialApp小部件隐式添加的。

若要修复该问题，请尝试以下操作：

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Test",
      home: TestPage(),
    );
  }
}

class TestPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Test")),
      body: Container(
        child: Center(
          child: RaisedButton(
            color: Colors.redAccent,
            textColor: Colors.white,
            onPressed: () {
              testAlert(context);
            },
            child: Text("PressMe"),
          ),
        ),
      ),
    );
  }

  void testAlert(BuildContext context) {
    var alert = AlertDialog(
      title: Text("Test"),
      content: Text("Done..!"),
    );

    showDialog(
        context: context,
        builder: (BuildContext context) {
          return alert;
        });
  }
}

票数 31

Stack Overflow用户

发布于 2019-10-16 16:10:07

在我的例子中，一个简单的解决方法就是简单地将MaterialApp小部件移动到main()方法。

main() {
  runApp(MaterialApp(home: App()));
}

票数 34

Stack Overflow用户

发布于 2020-07-28 04:18:06

当您切换到不受GlobalMaterialLocalizations委托支持的语言时，也会发生这种情况。这是一个很难理解的信息，因为它说你应该把MaterialApp放在树的顶端，但它可能已经存在了。

在我的例子中，我正在本地化的语言(英国威尔士语- cy-GB)不会自动满足需求。我必须为样板字符串编写自己的委托，并将其添加到应用程序根目录的本地化列表中。

白俄罗斯代表的代码是这里。我调整了它以迎合威尔士语。它包含日期格式信息，以及材料设计认为您可能需要的大约70个股票短语，如“选择所有”、“页面of”等。

如果您需要创建一个包含未在全局材料本地化中列出的语言的委托，那么一旦创建了委托，查看代码基，然后在树的顶部附近有一行如下

MaterialApp(
 localizationsDelegates: [
   GlobalMaterialLocalizations.delegate,
   GlobalWidgetsLocalizations.delegate,
   GlobalCupertinoLocalizations.delegate,
 ],
 supportedLocales: [
    const Locale('en', ''), // English, no country code
    const Locale('he', ''), // Hebrew, no country code
    const Locale.fromSubtags(languageCode: 'zh')
  ],
  // ...
)