忽略从JSArray到List< String>的转换失败 [英] Ignoring cast fail from JSArray to List<String>

问题描述

我从api使用字符串数组接收json。然后将其设置为类型为List的局部变量。

I receive json from api with string array. Then I set it to local variable with type List.

if (json['x'] is List) {
  List<String> x = json['x'];
  print(x);
}

当我运行应用程序时，Chrome会向我显示警告：忽略强制转换失败JSArray列出

When I run application, Chrome show me a warning: "Ignoring cast fail from JSArray to List"

我该怎么办？

• Angular 5.0.0-alpha + 6


• Chrome 63.0.3239.132


• Dart VM版本：2.0.0 -dev.32.0

推荐答案

JSON将所有数组编码为 List<动态> ，因为这是规范。

JSON encodes all arrays as List<dynamic>, since that is the specification.

如果您想将某些内容投射到 List< String> ，您不能像在Dart 2中那样仅依赖隐式转换。您必须使用实型：

If you want to cast something to List<String>, you can't rely on just an implicit cast like you did in Dart 2. You must either use the real type:

List x = json['x'];

或使用 .cast 函数：

var x = (json['x'] as List).cast<String>();

我意识到这比以前写的更多。如果您不喜欢样板，则可能需要查看JSON序列化程序包，例如 json_serializable 或 built_value 解决这个问题。

I realize that is more writing than before. You might want to look at JSON serialization package such as json_serializable or built_value if you don't like the boiler-plate around this.

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