Angular 5同步HTTP调用

Question

我有一个Angular 5应用程序,我必须调用一些繁重的REST服务(通常需要几秒钟).我需要在应用程序的不同部分使用它的结果,所以我想将结果存储在DataStorageService中.基本上,这是我想实现的:

@Injectable()
export class DataStorageService {

private result: MyCustomObject;

constructor(private service: Service) {}

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

问题是我如何等待HTTP请求完成,然后保存并返回'result'对象.我试图用Promise和Observable来解决它,但是没有一个能正常工作.

1. 观察到:

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

2. 诺言:

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

Answer 1

尝试使用 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;
}