3

我正在使用 angular2 和 electron 编写一个桌面应用程序,并且有一个下载功能。

DownloadService的是这个

import {Injectable} from '@angular/core';
import {Subject} from "rxjs";

interface IQueueItem {
    url: string
}

@Injectable()
export class DownloadService {
    private queue: Array< IQueueItem > = [];

    private downloadSubject: Subject<any>;

    constructor() {
        this.downloadSubject = new Subject();
    }

    addToList(item: IQueueItem) {
        this.queue.unshift(item);

        downloadList();

        return this.downloadSubject;
    }

    downloadList() {
        // pick one item from queue and send it to electron to download and store

        // do this every time a chunk of data received
        this.downloadSubject.next(evt);
        ...
    }

    pauseDownload(item) {
        // send an event to electron to it should stop downloading and therefore no chunk of data will receive
        // also remove item from queue
        ...
    }
}

ItemComponent的是这样的:

import {Component} from '@angular/core';
import {DownloadService} from "../services/download.service";

@Component({
    selector: 'app-item',
    template: `
        ...
      `
})
export class ItemComponent {
    constructor(private downloadService: DownloadService) {
        this.addToQueue();
    }

    subscription;

    downloadedBytes = 0;

    fileUrl = '';

    pause() {
        this.downloadService.pauseDownload(this.fileUrl);

        this.subscription.unsubscribe();

        ...
    }

    resume() {
        this.addToQueue();
    }

    private addToQueue() {
        this.subscription = this.downloadService.addToList(this.fileUrl)
            .subscribe(evt => {

                console.log(evt.delta);

                this.downloadedBytes += evt.delta;
            });
    }
}

问题是当我暂停一个我取消订阅的项目SubjectDownloadService,当我再次恢复时,每次console.log()打印两次并将两次数据添加到downloadedBytes. 此外,如果我再次暂停并恢复,它将添加越来越多的字节和日志!

我搜索了但我找不到任何线索来解决。

4

1 回答 1

2

您可以从yurzui创建的PLUNKER中看到,如果您恢复暂停一切都按预期工作,仅触发一次
问题是当您连续两次单击恢复时,第一个订阅将丢失在内存中,只有第二个将存储在this.subscription中,对第一个的访问将丢失,您无法取消订阅。

这更像是一个应用程序问题而不是 rxjs,如果订阅没有暂停,您应该无法单击恢复,因此您需要正确处理状态,如下所示(编辑自 @yurzui plunker):

@Component({
  selector: 'my-app',
  template: `
    <h1>Angular 2 Systemjs start</h1>
    <button *ngIf="started && !paused" (click)="pause()">Pause</button>
    <button *ngIf="started && paused" (click)="resume()">Resume</button>
    <button *ngIf="!started" (click)="start()">Start</button>
  `
})
export class App {
  constructor(private downloadService: DownloadService) {
    this.addToQueue();
  }

  subscription;
  downloadedBytes = 0;
  started = false;
  paused = false;


  pause() {
    this.paused = true;  

    this.subscription.unsubscribe();
  }

  start() {
    this.started = true;  

    this.addToQueue();
  }

  resume() {
    this.paused = false;

    this.addToQueue();
  }

  private addToQueue() {
    this.subscription = this.downloadService.addToList(this)
      .subscribe(evt => {

        console.log(11);

        this.downloadedBytes += evt.delta;
      });
  }
}

您可以在这个更新的PLUNKER中找到一个工作示例

于 2016-12-25T10:48:12.747 回答