飞镖中的NoSuchMethod？

Question

尝试使用 noSuchMethod() 时收到警告。

The method missing isn't defined for the class Person.

但是根据文档和其他示例，每当我们调用一个不存在的成员时，都应该调用 noSuchMethod()。其默认行为是抛出 noSuchMethodError。

 void main() {
    var person = new Person();
    print(person.missing("20", "Shubham")); // is a missing method!
 }

 class Person {

    @override
    noSuchMethod(Invocation msg) => "got ${msg.memberName} "
                      "with arguments ${msg.positionalArguments}";

 }

Answer 1

根据官方文档调用未实现的方法，你必须满足以下几点之一：

接收器具有静态类型动态。
接收器具有定义未实现方法的静态类型（抽象是可以的），接收者的动态类型有一个 noSuchMethod() 的实现与 class 中的不同对象。

示例 1：首先满足点

class Person {
  @override  //overring noSuchMethod
    noSuchMethod(Invocation invocation) => 'Got the ${invocation.memberName} with arguments ${invocation.positionalArguments}';
}

main(List<String> args) {
  dynamic person = new Person(); // person is declared dynamic hence staifies the first point
  print(person.missing('20','shubham'));  //We are calling an unimplemented method called 'missing'
}

示例 2：满足点秒

class Person {
  missing(int age,String name);

  @override //overriding noSuchMethod
    noSuchMethod(Invocation invocation) => 'Got the ${invocation.memberName} with arguments ${invocation.positionalArguments}';
}

main(List<String> args) {
  dynamic person = new Person(); //person could be var, Person or dynamic
  print(person.missing(20,'shubham')); //calling abstract method
}

飞镖中的NoSuchMethod？

NoSuchMethod in dart?

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