角度2不透明令牌 [英] angular 2 OpaqueToken

问题描述

在提供OpaqueToken方面需要一些帮助.使用Angular 2 beta-12.如果提供程序密钥是字符串，则可以正常工作，但在使用OpaqueToken时不起作用.在Child类中，SF未定义.

Need some help with providing an OpaqueToken. Using Angular 2 beta-12. It works fine if provider key is a string, but doesn't work when using OpaqueToken. In Child class, SF is undefined.

父级:

export let SF = new OpaqueToken('sf');

export class A {
  testMsg: string = 'hello';
}

@Component({
  template: `<child></child>`,
  providers: [
    provide(SF, {useValue: A}),
    provide('justString', {useValue: 'hi'}) 
  ]
})
export class App {}

儿童班:

import {Component, Injector, Inject, OpaqueToken} from 'angular2/core'
import {SF, A} from './app'
console.log("******", SF); // undefined
@Component({
  selector: 'child',
  template: `
    $$CHILD Rendered$$ {{a}}
  `
})
export class Child {
  //constructor(@Inject(SF) private a: A) {} // doesn't work
  constructor(@Inject('justString') private a: string) {}
}

我得到的例外:

angular2.min.js:17EXCEPTION:无法解析"Child"(@ Inject(未定义))的所有参数.确保所有参数都用Inject修饰或具有有效的类型注释，并确保'Child'用Injectable修饰.

angular2.min.js:17EXCEPTION: Cannot resolve all parameters for 'Child'(@Inject(undefined)). Make sure that all the parameters are decorated with Inject or have valid type annotations and that 'Child' is decorated with Injectable.

推荐答案

这是因为在包含父类和子类的模块之间存在循环依赖性.

It's because you have a cyclic dependency between modules that contain parent and child classes.

如果您将不透明令牌定义到第三个模块中，并将其包含在其他模块中，它将起作用.

If you define your opaque token into a third module and include it in the other ones, it will work.

例如常量模块:

export let SF = new OpaqueToken('sf');

在其他两个模块中:

import { SF } from './constants';

这篇关于角度2不透明令牌的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！