我只是试图创建一个带有按钮的应用程序，当按下按钮时该按钮会显示一条警告消息。

但这给了我这个错误（下面提到）。

我通过参考此视频编写了此代码。

我正在使用adb connect在实时Android手机上运行该应用程序

请帮忙..！

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;
        }
    );
  }
}

这是我写的代码。我还尝试将testAlert（）函数的内容直接插入onPressed，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