Angular 5 synchronous HTTP call

问题

I have an Angular 5 application in which I have to call some heavy REST service (usually takes some seconds). I need its result in different part of application, so I would like to store the result in a DataStorageService. Basically, this is I would like to achieve:

@Injectable()
export class DataStorageService {

private result: MyCustomObject;

constructor(private service: Service) {}

getResult(): MyCustomObject {
    if (typeof this.result === 'undefined') {
        // save result
    }
    return result;
}

The question is how I can wait until HTTP request is finished and then save and return the 'result' object. I tried to solve it using Promise and Observable as well, but none of them worked fine.

1. Observable:

   if (typeof this.result === 'undefined') {
       this.service.call()
           .subscribe(response => this.result = response);
   }
   return this.result;  // wait for save and return MyCustomObject
   

2. Promise:

   if (typeof this.result === 'undefined') {
       this.service.call()
           .toPromise()
           .then(response => this.result = response);
   }
   return this.result;  // wait for save and return MyCustomObject
   

回答1:

Try using await/async

async getResult(): Promise<MyCustomObject> {
    if (typeof this.result === 'undefined') 
    {
        // save result
        this.result = await this.service.call()
        .toPromise()
        .then(resp =>resp as MyCustomObject);//Do you own cast here

    }
    return this.result;
}

回答2:

The question is how I can wait until HTTP request is finished and then save and return the 're sult' object.

// Code in service:

ServiceMethod:Observabke<any>(){
     if (typeof this.result === 'undefined') {
                return this.service.call().map(res=>res);
}

// This is code in component.

 componentMethod(){


        return this.service.ServiceMethod()
            .subscribe(response => {
                this.result = response;
               },
               ()=>//handle error,
               () => // call completed { return this.result;  // Subscriber});
    }
    return this.weeklyPlayer;  // MyCustomObject (This return won't wait for http to get completed. Not sure why you want multiple returns.)

    }

Hope this helps.

来源：https://stackoverflow.com/questions/49444816/angular-5-synchronous-http-call