對象內數組訂購後未定義

Question

我試圖讓多個http請求後的元素，但有一個異步問題，我無法解決。發佈我的代碼：

Get函數在我的服務：

get() { 
return new Observable(project => { 
    this.channelsService.get().subscribe(
    stations => { 
     this._stations = stations; 
     this._stations.forEach((station) => { 
     station.cssClass = this.channelsService.getCss(station.id.split('/').pop()); 
     station.plstation$thumbnails = this.channelsService.getThumbnails(station.id.split('/').pop()); 
     if (station.plstation$callSign !== '') { 
      const watchliveUrl = this.watchLiveApi + station.plstation$callSign + '/?schema=1.0.0'; 
      this.http.get(watchliveUrl).subscribe(data => { 
      const body = data.json(); 
      station.currentListing = body.currentListing; 
      station.nextListing = body.nextListing; 
      project.next(stations); 
      project.complete() 
      }); 
     } 
     }); 

    }, (error) => { 
     this.mapErrorService.mapError(error, 'Listing service (1)'); 
    }); 
}); 

}

的get（）使用和訂閱：

constructor(private listingService: ListingService) { 
this.listingService.get().subscribe((stations) => { 
    this.stripDetails.channelList = stations; 
    // stations[6].currentListing Not undefined 
    console.log(stations); 
    // Now is undefined 
    console.log(stations[6].currentListing); 

}); } 

我如何定義站[6] .currentListing ？

Answer 1

您正在將Observable從http.get()轉換爲Promise，但您絕不會對該Promise做任何事情。因此，雖然stations被定義在你說的地方，但Promise不會完成，所以currentListing屬性將是未定義的。

使用Observable或Promise時，您必須始終等待結果。因此，在這種情況下，如果您要使用承諾，則需要將它們彙總在一起，並且不會輸出project，直到它們全部完成。

喜歡的東西：

get() { 
return new Observable(project => { 
    this.channelsService.get().subscribe(
    stations => { 
     this._stations = stations; 
     let responses = this._stations.map((station) => { 
     station.cssClass = this.channelsService.getCss(station.id.split('/').pop()); 
     station.plstation$thumbnails = this.channelsService.getThumbnails(station.id.split('/').pop()); 
     if (station.plstation$callSign !== '') { 
      const watchliveUrl = this.watchLiveApi + station.plstation$callSign + '/?schema=1.0.0'; 
      return this.http.get(watchliveUrl).map(data => { 
      const body = data.json(); 
      station.currentListing = body.currentListing; 
      station.nextListing = body.nextListing; 
      }); 
     } 
     }); 
     // Wait for all requests to complete. 
     Rx.Observable.forkJoin(...responses).subscribe(() => { 
      project.next(stations); 
      project.complete() 
     }); 

    }, (error) => { 
     this.mapErrorService.mapError(error, 'Listing service (1)'); 
    }); 
});