Flutter:我在运行时遇到了这个问题:flutter pub run build_runner watch

Question

这是错误:

Bad state: Unexpected diagnostics:
C:\flutter\bin\cache\dart-sdk\lib\internal\internal.dart:172:16 - This requires the 'non-nullable' 
language feature to be enabled.
[SEVERE] json_serializable:json_serializable on test/widget_test.dart:

这只是在最后一次 flutter 升级之后发生的。我尝试了很多解决方案，但没有任何效果，即使我重新安装了 flutter SDK。

这是 pubspec.yaml :

environment:
 sdk: ">=2.7.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  json_annotation: ^3.0.1
  cupertino_icons: ^0.1.3

dev_dependencies:
  flutter_test:
    sdk: flutter
  build_runner:
  json_serializable: ^3.3.0

测试代码:

import 'package:json_annotation/json_annotation.dart';

part 'test.g.dart';

//@JsonSerializable(nullable: true)
//@JsonSerializable(nullable: false)
@JsonSerializable()
class Test{
  final String test;
  Test(this.test);
}

Answer 1

解决这个问题的最简单方法

将环境 sdk 降级到 2.1.0

像这样

environment:
  sdk: ">=2.1.0 <3.0.0"