依赖注入 – 如何在Angular2中正确使用依赖注入？

我在解决DI问题方面取得了成功.我已经阅读了一些教程并获得了jist但是在使用我的自定义服务制作了一些嵌套的DI后,事情开始崩溃了.

有人可以解释何时使用useFactory而不是useClass？我已经看过ng2文档,我已经看过这些例子,但是我无法将它们映射到我的问题中.目前我的引导程序看起来像这样：

bootstrap(
    App,[
        FORM_PROVIDERS,ROUTER_PROVIDERS,HTTP_PROVIDERS,provide(LocationStrategy,{ useClass: PathLocationStrategy }),provide(RequestOptions,{ useClass: DefaultRequestOptions }),provide(MsgService,{ useClass: MsgService }),provide(HttpAdvanced,{ useFactory: (MsgService,HTTP_PROVIDERS) => new HttpAdvanced(MsgService,HTTP_PROVIDERS),deps: [MsgService,HTTP_PROVIDERS] }),provide(AuthService,{ useFactory: (HttpAdvanced) => new AuthService(HttpAdvanced),deps: [HttpAdvanced,MsgService] }),provide(FormBuilderAdvanced,{ useFactory: (FormBuilder,HttpAdvanced) => new FormBuilderAdvanced(FormBuilder,HttpAdvanced),deps: [FormBuilder,HttpAdvanced] }),provide(MsgServiceInternal,{ useClass: MsgServiceInternal })
    ]
);

我的最新一期是：

EXCEPTION: Error during instantiation of AuthService! (HeaderBar -> AuthService).
ORIGINAL EXCEPTION: TypeError: this.http.get is not a function

我的依赖项就像

HttpAdvanced        -> Http(ng2),MsgService
MsgService          -> MsgServiceInternal
AuthService         -> HttpAdvanced
FormBuilderAdvanced -> FormBuilder(ng2),HttpAdvanced

1.我是否正确使用了provide / useClass / useFactory,我如何提供具有其他依赖关系的服务？

此外,我在我的代码中的一个地方：

static isUserInjector() {
    return (next,prev) => Injector.resolveAndCreate([AuthService,{ useClass: HttpAdvanced })]).get(AuthService).isUser();
}

因为我想拥有一个我提供的功能

@CanActivate(AuthService.isEditorInjector())

但是我不能使用构造函数注入,因为@CanActivate在类范围之外,所以我不能在控制器中注入服务然后引用像@CanActivate(this.authService.isEditor())

2.对此有什么好的解决方案？

一些代码：

@Component({
    selector: 'ShowStats',templateUrl: './dest/views/showStats/showStats.html',directives: [ COMMON_DIRECTIVES,UsersCount,AdminsList,GlobalWishlist,PopularTrack ]
})
export class ShowStats {
    authService : AuthService;

    constructor( authService : AuthService ){
        this.authService = authService;
    }
}

... next file ...

@Injectable()
export class HttpAdvanced {
    msgService: MsgService;
    http: Http;

    constructor(msgService: MsgService,http: Http) {
        this.msgService = msgService;
        this.http = http;
    }

    /*
     * This is for plain ol' GET requests .. with callback of course.
     */
    public get(url,callback) {
        return this.http.get(url).subscribe((res) => {
            let data = res.json().data;
            callback(data);
        },this.msgService.httpErrorHandler);
    }
.... other code for HttpAdvanced

3.
导入文件的顺序对DI是否重要？我想我注意到,因为我在同一个文件中有MsgService和MsgServiceInternal,并且MsgService依赖于Internal,我之前必须放置Internal但是我不是100％它是否与导入顺序相同？

4.
所以,如果我只是这样做：

bootstrap(
    App,MsgService,HttpAdvanced,AuthService,FormBuilderAdvanced,MsgServiceInternal
    ]
);

我明白了：

Cannot resolve all parameters for 'FormBuilderAdvanced'(?,?). 
Make sure that all the parameters are decorated with Inject or have 
valid type annotations and that 'FormBuilderAdvanced' is decorated 
with Injectable.

我曾经用useFactory删除这个错误,但我现在很困惑.这是否意味着没有注入deps,因为它看不到它们或什么？

Form类：

export class FormBuilderAdvanced {
    http: HttpAdvanced;
    fb: FormBuilder;

    constructor(fb: FormBuilder,http: HttpAdvanced) {
        this.fb = fb;
        this.http = http;
    }

    create(controlNames: string[],submissionUrl: string,getter?: any) {
        return new Form(this.fb,this.http,controlNames,submissionUrl,getter);
    }
}

bootstrap(
    App,// provide(MsgService,// is just fine when no special behavior is required
        // provide(HttpAdvanced,provide(Http,{useClass: HttpAdvanced});
        AuthService,provide(FormBuilder,{ useClass: FormBuilderAdvanced}),MsgServiceInternal)
    ]
);

如果要使类可用于注入,只需将类型添加到提供者列表(提供(AuthService),只需要AuthService执行相同操作).
如果要注入与请求的类不同的类,请使用useClass.

例

@Injectable()
export class MyService {
  constructor(private http: Http) {
  }
}

如果您的提供商包含

provide(Http,{useClass: HttpAdvanced});

然后MyService(它依赖于Http)会被注入HttpAdvanced.
确保在HTTP_PROVIDERS之后使用此行来覆盖HTTP_PROVIDERS中包含的默认Http提供程序.

如果DI本身不能解决依赖关系,因为它们不仅仅是其他提供者,那么使用useFactory.

正如刚才提到的,

Ensure you have this line after HTTP_PROVIDERS to override the default Http provider,contained in HTTP_PROVIDERS.

提供商列表中的顺序很重要.
当提供者列表包含多个类型的提供者时,则仅使用最后一个.

进口的顺序无关紧要.

一个文件中依赖类的顺序很重要,因为类没有被提升.

例

export class ClassA {
   // constructor(private b: ClassB) {} // ClassB is unknown here
   constructor(@Inject(forwardRef(() => DataService)) {
   }
}

export class ClassB {
}

如果ClassB的代码高于ClassA,则不需要forwardRef().

另见Class is not injectable if it is defined right after a component with meta annotation

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