我怎样才能从angular2的构造函数中传递字符串参数或数字 [英] how can I pass string parameter or number from constructor in angular2

问题描述

在angular2的打字稿中，我需要在构造函数中传递字符串参数或什至number参数，如下所示:构造函数(_para:string){}但是生成错误，调试器不断告诉我:

In angular2 for typescript , I need to pass string parameter or even number parameter in the constructor as the following : constructor(_para:string) {} but generating an error and the debugger keep telling me :

NoProviderError {消息:没有字符串提供者！(应用程序->字符串)"，堆栈:错误:DIException↵在NoProviderError.BaseExc…ularjs.org/2.0.0-beta.8/angular2.dev.js:11284:19)"

NoProviderError {message: "No provider for String! (App -> String)", stack: "Error: DI Exception↵ at NoProviderError.BaseExc…ularjs.org/2.0.0-beta.8/angular2.dev.js:11284:19)"

如果我删除_para:string，它将起作用....这是plnkr中的Demoe:

if I remove _para:string , it will work .... here is the Demoe in plnkr :

http://plnkr.co/edit/t7serY3L6LtvzYc5xHtL?p=preview

and here is the code : 
//our root app component
import {Component} from 'angular2/core'

@Component({
  selector: 'my-app',
  providers: [],
  template: `
    <div>
      <h2>Hello {{name}}</h2>


    </div>
  `,
  directives: []
})
export class App {
  constructor(_para:string) {

    this.name = 'Angular2'
  }
}

推荐答案

对于由Angulars依赖项注入(DI)创建的组件，它将尝试查找提供程序，并使用构造函数参数的类型作为关键字来查找一个提供程序.

For components created by Angulars dependency injection (DI), it tries to find providers and uses the type of the constructor parameters as key to find one.

诸如 string ， number ， boolean ， Object 之类的原始类型不能用作键.如果要使用此类泛型"类型，则需要一个人工密钥.除支持键外，DI还支持字符串或 OpaqueToken 作为键类型.对于此类人工键，您需要使用 @Inject()装饰器.

Primitive types like string, number, boolean, Object don't work as keys. If you want to use such "generic" types you need an artifical key. DI supports a string or OpaqueToken as key in addition to types. For such artifical keys you need to use the @Inject() decorator.

bootstrap(MyApp, [provide('para': {useValue: 'Hello World!'})]);

@Component({
  selector: 'my-app',
  providers: [],
  template: `
    <div>
      <h2>Hello {{name}}</h2>


    </div>
  `,
  directives: []
})
export class App {
  constructor(@Injet('para') _para:string) {

    this.name = 'Angular2'
  }
}

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