Flutter 异常: The getter ‘modalBarrierDismissLabel’ was called on null. Receiver: null Tried calling:

Myth丶恋晨 2023-02-14 13:08 163阅读 0赞

### Flutter 异常: The getter ‘modalBarrierDismissLabel’ was called on null. Receiver: null Tried calling: ###

*  1.问题场景
 *  2.解决方案

一般出现这种问题都是直接在 `MaterialApp` 层显示 `Dialog` 造成的，因为显示 `Dialog` 传入的是 `MaterialApp` 层的 `context`，所以会出现这种错误。

# 1.问题场景 #

import 'package:flutter/cupertino.dart';
    import 'package:flutter/material.dart';
    
    void main() { 
      runApp(MyApp());
    }
    
    class MyApp extends StatelessWidget { 
      @override
      Widget build(BuildContext context) { 
        return MaterialApp(
          home: Scaffold(
            appBar: AppBar(
              title: Text('Demo'),
            ),
            body: Center(
              child: RaisedButton(
                onPressed: () { 
                  showCupertinoDialog(
                      ///此处传入的是 MaterialApp 的 context
                      context: context,
                      builder: (context) { 
                        /// 此处省略弹窗代码
                      }
                  }
                },
                child: Text('点击显示弹窗'),
              ),
            ),
          ),
        );
      }
    }

因为 `context` 是 `MaterialApp` 的，所以会报这样的错：

════════ Exception caught by gesture ════════
    The following NoSuchMethodError was thrown while handling a gesture:
    The getter 'modalBarrierDismissLabel' was called on null.
    Receiver: null 
    Tried calling: modalBarrierDismissLabel

# 2.解决方案 #

直接在 `MaterialApp` 的 `home` 中在传入一个继承于 `StatelessWidget` 或者是 `StatefulWidget` 的部件即可。如：

import 'package:flutter/cupertino.dart';
    import 'package:flutter/material.dart';
    
    void main() { 
      runApp(MyApp());
    }
    
    class MyApp extends StatelessWidget { 
      @override
      Widget build(BuildContext context) { 
        return MaterialApp(
          home: DialogPage(),
        );
      }
    }
    
    class DialogPage extends StatelessWidget { 
      @override
      Widget build(BuildContext context) { 
        return Scaffold(
          appBar: AppBar(
            title: Text('Demo'),
          ),
          body: Center(
            child: RaisedButton(
              onPressed: () { 
                _showDialog(context);
              },
              child: Text('点击显示弹窗'),
            ),
          ),
        );
      }
    }
    
    void _showDialog(widgetContext) { 
      /// 显示 IOS 风格的 CupertinoAlertDialog
      showCupertinoDialog(
        context: widgetContext,
        builder: (context) { 
          return CupertinoAlertDialog(
            title: Text('确认删除'),
            actions: [
              CupertinoDialogAction(
                child: Text('确认'),
                onPressed: () { 
                  Navigator.of(context).pop();
                },
              ),
              CupertinoDialogAction(
                child: Text('取消'),
                isDestructiveAction: true,
                onPressed: () { 
                  Navigator.of(context).pop();
                },
              ),
            ],
          );
        },
      );
    }