例外：未找到MaterialLocalizations。在尝试显示AlertDialog时

Question

尝试通过从父窗口小部件调用函数来显示警报对话框。

这是代码：

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: RaisedButton(
            onPressed: () {
              popUp(context);
            },
            child: Text("Click"),
          ),
        ),
      ),
    );
  }

  void popUp(BuildContext context) {
    showDialog(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(title: Text("ok"),);
      },
    );
  }
}

但是获得以下异常：

I/flutter ( 4041): ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
I/flutter ( 4041): The following assertion was thrown while handling a gesture:
I/flutter ( 4041): No MaterialLocalizations found.
I/flutter ( 4041): MyApp widgets require MaterialLocalizations to be provided by a Localizations widget ancestor.
I/flutter ( 4041): Localizations are used to generate many different messages, labels,and abbreviations which are used
I/flutter ( 4041): by the material library. 
I/flutter ( 4041): To introduce a MaterialLocalizations, either use a  MaterialApp at the root of your application to
I/flutter ( 4041): include them automatically, or add a Localization widget with a MaterialLocalizations delegate.
I/flutter ( 4041): The specific widget that could not find a MaterialLocalizations ancestor was:
I/flutter ( 4041):   MyApp
I/flutter ( 4041): The ancestors of this widget were:
I/flutter ( 4041):   [root]

它读取我已经完成的use a MaterialApp at the root of your application。我在这做错了什么？

Answer 1

问题是你传递给context函数的popUp变量实际上来自根。如果这是有意义的，它不包含在MaterialApp内。

要解决这个问题，您可以重构您的小部件以使body成为它自己的小部件，或者使用Builder，如：

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Builder(builder: (context) => Center(
          child: RaisedButton(
            onPressed: () {
              popUp(context);
            },
            child: Text("Click"),
          ),
        )),
      ),
    );
  }