Flutter：@required关键字 [英] Flutter: @required keyword

问题描述

我不太了解 @required 的工作方式。例如，我看过以下代码：

I don't really understand how @required works. For example I've seen this code:

class Test{
  final String x;
  Test({
    @required this.x
  });

  factory Test.initial(){
    return Test(x: "");
  }

}

但是<$ c $应该是什么c> @required 在这里做什么？好像它使可选参数成为非可选参数。

But what should @required do here? Seems like it makes an optional parameter a non optional parameter.

推荐答案

@required ，您可以使用 @required 对其进行注释。

@required is needed when you have more than 1 named parameters and you want some of the parameters to be mandatory, you annotate it using @required.

示例

class Test {
  final String a; // say a is mandatory
  final String b;
  final String c;
  final String d;

  Test({
    @required this.a, // annotate it using required
    this.b,
    this.c,
    this.d,
  });
}

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