Life-cycle methods for services in angular2 [duplicate]

Question

Is it possible to have life-cycle hooks for a service that is annotated with @Injectable()?

I'd have expected the life-cycle hooks to be called on a service like this, but I was proven wrong, it seems to be working on @Component only. Is there a way to get informed in a service when dependency injection creates / destroys a service?

import {Component, Injectable, OnInit, OnDestroy} from 'angular2/core';

@Injectable()
export class SampleService implements OnInit, OnDestroy {
    ngOnInit() {
        console.log("OnInit")
    }
    ngOnDestroy() {
        console.log("OnDestroy")
    }
}

@Component({
  selector: "sample",
  template: "<div>Sample Component</div>",
  providers: [ SampleService ]
})
export class SampleComponent {
  constructor() { private _sampleService: SampleService }
}

This isn't a duplicate of the other question because it also mentions OnDestroy whereas the other question only mentions OnInit. The documentation for OnDestroy actually states that services should support it. I was also proven wrong. — Patrick Graham
In your case, I think its the approach you're taking might be the wrong way around. Injectables/Services are simply tools to get data and such. If you want a life-cycle hook to have the service do something on start, I would suggest putting the ngOnInit hook on your main app Component, that would make a call to the injected service to kick it off. Basically use the main app component to kick off the service, which will keep you parts as they are. It's all about perspective. ;) — Guy Park
@GuyPark: That's basically what I do as a workaround. I had hoped for the life-cycle of the service to be more automatic, but I understand the problems involved, so yes, that's a valid solution. — Martin C.

poke poke · Accepted Answer · 2016-03-23T21:40:01

Injectables are just normal classes (normal objects) and as such, they have no special lifecycle.

When an object of your class is created, the class’s constructor is called, so that’s what your “OnInit” would be. As for the destruction, a service does not really get destroyed. The only thing that might happen is that it gets garbage collected once there is no longer a reference to it, which likely happens after the dependency injector is removed itself. But you generally have no control over it, and there is no concept of a deconstructor in JavaScript.

@Injectable()
export class SampleService {
    constructor() {
        console.log('Sample service is created');
    }
}

Life-cycle methods for services in angular2 [duplicate]

2 Answers