哪里最好注册Angular 2提供者

Question

I wrote three services for an Angular 2 app, with the configuration that two are injected into the third and used there. After importing the two (all three decorated with @Injectable() ), I still received an unknown provider error.

To solve it I attempted to place the injected services into the modules providers array, which worked. Is this the best approach?

Angular documentation shows listing injectables at the component level. Can I just place all injectables into the modules providers array?

Seems like this would simplify application setup as everything is configured in a central location for each module. No searching for dependencies on a component by component basis.

Answer 1

Yes, put it in the @NgModule.providers if the service is to be application scoped (singleton). Only add it to the @Component.providers if the service should be component scoped ¹ (each component should get its own instance)

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_{1 - See also Hierarchical Injectors}

Answer 2

It depends upon your requirement that what kind of service you want.

Singleton service

If you want to use singleton service , you can place your service somewhere in central area. You will think you should use/place service in AppModule . But still to achieve true singleton pattern/instance you should place/declare service in CoreModule-please check how to user CoreModule and then import CoreModule to AppModule .

Multiple Instance service

If you declare serivce in @Component decorator of the components, you will have different instances of the service in different components.