我能不能在 List 中的 if 语句里写花括号？

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我能不能在 List 中的 if 语句里写花括号？

以下未添加大括号的代码运行良好:

import 'package:flutter/material.dart';
void main() {
  runApp(const _MyApp());
}
class _MyApp extends StatelessWidget {
  const _MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    const isFlag = true;
    return MaterialApp(
      home: Scaffold(
        body: Column(
          children: const [
            Text(
              "Demo1",
            ),
            if (isFlag)
              Text(
                "Demo true",
              )
            else
              Text(
                "Demo flase",
              )
          ],
        ),
      ),
    );
  }
}

即使只有一个表达式，我也更喜欢添加大括号。

我做了以下尝试，但导致错误。

导致错误的代码:

import 'package:flutter/material.dart';
void main() {
  runApp(const _MyApp());
}
class _MyApp extends StatelessWidget {
  const _MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    const isFlag = true;
    return MaterialApp(
      home: Scaffold(
        body: Column(
          children: const [
            Text(
              "Demo1",
            ),
            if (isFlag) {
              Text(
                "Demo true",
              )
            } else {
              Text(
                "Demo flase",
              )
            }
          ],
        ),
      ),
    );
  }
}

错误:

lib/main.dart:21:25: Error: A value of type 'Set' can't be assigned to a variable of type 'Widget'.
 - 'Set' is from 'dart:core'.
 - 'Text' is from 'package:flutter/src/widgets/text.dart'
 ('../../../flutter-command/flutter/packages/flutter/lib/src/widgets/text.dart').
 - 'Widget' is from 'package:flutter/src/widgets/framework.dart'
 ('../../../flutter-command/flutter/packages/flutter/lib/src/widgets/framework.dart').
            if (isFlag) {
                        ^
lib/main.dart:25:20: Error: A value of type 'Set' can't be assigned to a variable of type 'Widget'.
 - 'Set' is from 'dart:core'.
 - 'Text' is from 'package:flutter/src/widgets/text.dart'
 ('../../../flutter-command/flutter/packages/flutter/lib/src/widgets/text.dart').
 - 'Widget' is from 'package:flutter/src/widgets/framework.dart'
 ('../../../flutter-command/flutter/packages/flutter/lib/src/widgets/framework.dart').
            } else {

我是否不能在List的if语句中编写大括号？

参考以下链接:

如何在Flutter Widget（居中Widget）的子属性中使用条件语句

附言:

问题只关于是否可以应用大括号。

我之所以提出这个问题，是因为我对Dart语法感兴趣。

admin 更改状态以发布 2023年5月22日
0

2 答案

0 Comments

用三元运算符像这样完成它

isFlag?Text("Demo true"):Text("Demo flase")

0
0 Comments

你正在使用花括号创建一个集合(Set)，想要了解更多关于集合的信息请访问集合。你的构建函数应该像这样：

return MaterialApp(
   home: Scaffold(
     body: Column(
       children: const [
         Text(
           "Demo1",
         ),
         if (isFlag)
           Text(
             "Demo true",
           )
         else
           Text(
             "Demo flase",
           )
       ],
     ),
   ),
);

或者你可以使用三目运算符，例如代码：

return MaterialApp(
   home: Scaffold(
     body: Column(
       children: const [
         Text(
           "Demo1",
         ),
         isFlag ? Text("Demo true",) : Text("Demo flase")
       ],
     ),
   ),
);

0