英文:
Angular dependency registration token type
问题
在下面的示例中，我想知道如何使用类型标记（type-token）来注册依赖项，而不是使用字符串标记（string-token），因为依赖关系是由一个类来表示的？在下面的示例中，service 可以轻松地通过useClass配置选项从一个类替换为另一个类（HeroService <-> NewheroService）。
如何重写这个示例，使得HeroListComponent构造函数的参数看起来像constructor( private service: MyService)？我尝试创建一个接口类MyService，其中HeroService和NewheroService继承自它。还将提供程序从'MyService'更改为MyService，但它会引发错误：
'MyService'只引用了一个类型，但在这里被用作值。
@Injectable()
export class HeroService {}
@Injectable()
export class NewheroService {}
hero.component.ts:
@Component({ ...,
providers: [{
provide: 'MyService',
useClass: HeroService
}]
})
export class HeroListComponent {
constructor(@Inject('MyService') private service: any) { }
}
如何重写这个示例，使得HeroListComponent构造函数的参数看起来像constructor( private service: MyService)？
我尝试创建一个接口类MyService，其中HeroService和NewheroService继承自它。还将提供程序从'MyService'更改为MyService，但它会引发错误：
'MyService'只引用了一个类型，但在这里被用作值。
英文:
Instead of using string-token in the example below, I want to know how to use type-token to register the dependency, because the dependency is represented by a class? In the following example, service can easily be substituted through useClass configuration option from one class to another (HeroService <-> NewheroService).
How to rewrite this example that the parameter of HeroListComponent constructor looks like constructor( private service: MyService)? I tried to create interface class MyService, where HeroService and NewheroService inherits from. Also changed provider from 'MyService' to MyService but it throws an error:
> 'MyService' only refers to a type, but is being used as a value here.
@Injectable()
export class HeroService {}
@Injectable()
export class NewheroService {}
hero.component.ts:
@Component({ ...,
providers: [{
provide: 'MyService',
useClass: HeroService
}]
})
export class HeroListComponent {
constructor(@Inject('MyService') private service: any) { }
}
答案1
得分: 1
这是关于注入令牌的主要用法：如果你曾经使用过Angular Material的对话框 (MAT_DIALOG_DATA)，那么你已经在过去使用过它们了。
const MY_SERVICE = new InjectionToken<string>('某个唯一标识符');
@Component({ ...,
providers: [{
provide: MY_SERVICE,
useClass: HeroService
}]
})
export class HeroListComponent {
constructor(@Inject(MY_SERVICE) private service: any) { }
}
英文:
That's the main use of injection tokens : you have already used them in the past if you have used angular material's dialog (MAT_DIALOG_DATA)
const MY_SERVICE = new InjectionToken<string>('Some unique identifier');
@Component({ ...,
providers: [{
provide: MY_SERVICE,
useClass: HeroService
}]
})
export class HeroListComponent {
constructor(@Inject(MY_SERVICE) private service: any) { }
}
答案2
得分: 1
你可以通过创建一个通用服务来实现。
export class GeneralService {
// 可以在这里定义通用方法或属性
}
然后你的服务可以继承它：
@Injectable()
export class HeroService extends GeneralService {
constructor(){super();}
}
@Injectable()
export class NewheroService extends GeneralService {
constructor(){super();}
}
然后在你的组件中可以像这样注入它：
@Component({ ...,
providers: [{
provide: GeneralService,
useClass: HeroService
}]
})
export class HeroListComponent {
constructor(private service: GeneralService) { }
}
GeneralService 可以注入到其他组件或服务中，Angular 的依赖注入会在使用接口的地方提供 HeroService 的实例。
Stackblitz: https://stackblitz.com/edit/angular-service-injection-e7s4k2?file=src%2Fapp%2Fhero.service.ts
英文:
You can do it by creating a general service.
export class GeneralService {
// Can be defined common methods or properties here
}
Then your services extends it:
@Injectable()
export class HeroService extends GeneralService {
constructor(){super();}
}
@Injectable()
export class NewheroService extends GeneralService {
constructor(){super();}
}
Then in your component you can inject it like this:
@Component({ ...,
providers: [{
provide: GeneralService,
useClass: HeroService
}]
})
export class HeroListComponent {
constructor(private service: GeneralService) { }
}
The GeneralService can be injected into other components or services, and Angular's dependency injection will provide the instance of HeroService wherever the interface is used.
Stackblitz: https://stackblitz.com/edit/angular-service-injection-e7s4k2?file=src%2Fapp%2Fhero.service.ts
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