Angular2中带有可选参数的依赖注入

Question

我有多个组件需要相同的依赖性，而构造函数需要一个字符串。我如何告诉 angular2 为 DI 使用特定类型的实例？

例如：

ChatUsers.ts:

@Component({
    selector: "chat-users"
})
@View({
    directives: [],
    templateUrl: '/js/components/ChatUsers.html'
})
export class ChatUsers {

    constructor(public currentUser : User) {
    }
}

和app.ts：

/// <reference path="../libs/typings/tsd.d.ts" />

import {Component, View, bootstrap} from 'angular2/angular2';

import {User} from "User";

// How to create a user, e.g. new User('John') and use it for DI?

@Component({
    selector: 'chat-app'
})
@View({
    directives: [ ],
    template: `
      <div> Some text
      </div>`
})
class ChatApp {
    constructor(public user: User) {
        // do something with user
    }


}
bootstrap(ChatApp, [ User ]);

User.ts

export class User {
    name: string;
    constructor(name: string) {
        this.name = name;
    }
}

如果运行这段代码，错误是：

Cannot resolve all parameters for User(?). Make sure they all have valid type or annotations.

我使用的是最新的 angular2 版本：2.0.0-alpha.44

Answer 1

要使依赖项可选，只需使用 @Optional parameter decorator (see this plunker):

class User {
  name: string;
  constructor(@Optional() name: string) {
    this.name = name;
  }
}

如果你想将 name 注入 User 你有两个解决方案：

将一些 'userName' 提供程序添加到应用程序提供程序并使用 @Inject('userName') parameter decorator to inject it into User (see this plunker)。

class User {
  name: string;
  constructor(@Inject('userName') name: string) {
      this.name = name;
  }
}
// ...
bootstrap(ChatApp, [
  User, 
  provide('userName', { useValue: 'Bob'})
]);

使用useFactory to specifically instantiate your user (see this plunker):

bootstrap(ChatApp, [
  provide(User, { useFactory: () => new User('John') })
]);

Angular2中带有可选参数的依赖注入

Dependency injection with optional parameter in Angular2

typescript

angular