如何从角度的单个函数返回订阅和承诺？

Question

我正在开发一个实现文件上传功能的 Angular 项目。 我创建了一个上传服务，并在其中创建了一个用于上传文件的函数

service.ts :

upload(file: File){
  return new Promise(resolve=>{
    var file = file;
    bucket.upload(file).on("httpUplaodprogress", (progress)=>{
        const percent = progress.percent

        -->  Here I want to emit this percent value from this function. and want to get it where it is from called.


    }).send(response =>{
      response.error ? reject(response.err);
      resolve(response);
    })
  })
}

现在很多地方都在使用这个上传服务。

例如：

uploadComponent.ts :

progress:number = 0;

constructor(private uploadService: UploadService) {}

handleFileInput(file){
    this.uploadService.upload(file).then(result=>{
       result ? show success msg for file uplaod success : show error

       ==> I want to subscribe service's upload function's progress variable 
           here for assign that value into this host component's progress variable which is 
           bind with progressbar copmponent.
   
    })
}

uploadComponent.html

<progressbar [progress]="progress" />

这是当前场景，我们无法将进度变量从服务函数访问到调用服务函数的主机组件。

一种方式是，我们可以将订阅服务功能获取到主机组件中，并且可以不断获取进度值。但是如何？

因为服务功能已经返回承诺。如何在 Promise 中使用订阅并将其订阅到主机组件中。

我还考虑过将全局订阅变量加入服务并将其订阅到主机组件中。但是从多个地方上传文件并显示进度条时可能会导致问题。

我想为每次调用保留订阅变量的本地范围。

如果有人知道它，如何从 Promise 函数广播值并在调用它的主机函数中接收..然后请回复。这对我很有帮助。

Answer 1

你应该从你的服务中返回一个 Observable 而不是一个 Promise。

UploadService

// note that BucketUploadResponse is an interface I made up
upload(file: File): Promise<BucketUploadResponse> {
     // delegate to our Observable implementation and convert to promise
     return this.upload$(file).toPromise();
}

// note that BucketUploadResponse is an interface I made up
upload$(file: File): Observable<number | BucketUploadResponse> {
        return new Observable<number>((subscriber) => {
            bucket
                .upload(file)
                .on('httpUplaodprogress', (progress) => {
                    const percent = progress.percent;
                    // emit progress
                    subscriber.next(percent);
                })
                .send((response) => {
                    if (response.error) {
                        // error out
                        subscriber.error(response.error);
                    } else {
                        // emit response as last item to keep old contract
                        subscriber.next(response);
                        subscriber.complete();
                    }
                });

            return () => {
                // called when no subscription is left. You could abort the upload here for example
            };
        });
    }

在消费组件中，可以订阅 Observable：

    progress:number = 0;
    
    private uploadSubscription?: Subscription;

    constructor(private uploadService: UploadService) {}

    handleFileInput(file){
        this.progress = 0;
        // unsubscribe from an existing upload
        this.uploadSubscription?.unsubscribe();
        this.uploadSubscription = this.uploadService.upload(file).subscribe((progress) => {
            if (typeof progress === 'number') {
                this.progress = progress;
            } else {
                // handle BucketUploadResponse if required
            }
        }, () => {
            // complete, show success message
        }, (error) => {
            // error, show error message
        })
    }

Answer 2

您可以将标头传递给您的 http 调用以订阅进度

reportProgress: true,
observe: 'events'

在你上传组件

yourservice.subscribe((e: HttpEvent<any>) => {
          switch (e.type) {
            case HttpEventType.Sent:
              break;
            case HttpEventType.ResponseHeader:
              break;
            case HttpEventType.UploadProgress:
              this.progress = Math.round(e.loaded / e.total * 100);
              break;
            case HttpEventType.Response:
              this.progress = -1;
          }
    });

或

如果您愿意，您可以选择实施行为主体以实现此目的 在您的 service.ts 中将 processPercentage 声明为行为主题

const percent = progress.percent;
this.processPercentage.next(percent);

在您的 uploadComponent.ts 中

subscription:Subscription;
constructor(private uploadService: UploadService,private service:Service) {}
ngOnInit(){
 this.getProgress();
}

getProgress(){
 this.subscription = 
 this.service.processPercentage.asObservable().susbcribe((progress) => {
  this.progress = progress;
  console.log(this.progress);
  // You can bind to your progressbar from here 
 });
}

ngOnDestroy(){
 this.subscription.unsubscribe();
}