Provide a service based on platform

Ionic Framework ionic-v3
#1

Hi.
I need to change some behaviors according to platform, so I created different platform-based services (with the same parent class).

Now I have to provide the right service. I think to use something like:

  var serviceClass = NameService;
  if (platform.is('ios') {
    serviceClass = IosNameService;
  } else if (platform.is('android') {
    serviceClass = AndroidNameService;
  }
  return { provide: NameService, useClass: serviceClass }

But platform is not ready on initialization time.

How can I reach the same result?

Thank you.

#2

If you don’t get any better answers, what I would do is ditch inheritance in favor of composition and delegation. From a DI consumer perspective, there is only NameService. Inside NameService there is a delegate object that you create explicitly.

export class NameService {
  private _delegate: IosNameService | AndroidNameService;
  private _ready: Promise<void>;

  constructor(plat: Platform) {
    this._ready = plat.ready().then(() => {
      if (plat.is('android')) {
        this._delegate = new AndroidNameService();
      } else if (plat.is('ios')) {
        this._delegate = new IosNameService();
      }
    });
  }

  ready(): Promise<void> {
    return this._ready;
  }

  frobulate(foo: string): string {
    return this._delegate.frobulate(foo);
  }
}
#3

Thank you @rapropos .

I adopted a similar solution:

export class PlatformBasedService {
    public nameService:NameService;

    constructor(plat: Platform) {
      this._ready = plat.ready().then(() => {
        if (plat.is('android')) {
          this.nameService = new AndroidNameService();
        } else if (plat.is('ios')) {
          this.nameService = new IosNameService();
        }
      });
    }
}

AndroidNameService and IosNameService implement NameService interface.

Pros:

  • Who uses nameService knows that is platform based.
  • Who implements AndroidNameService and IosNameService have to respect a common interface.

Cons:

  • Goodbye Angular service injection :slight_smile: