将PDF下载到UWP中的LocalFolder

Question

I've a UWP app that downloads a pdf file from a website to ApplicationData.Current.LocalFolder , but when I use the Explorer to open the downloaded file, its size is always 0KB and it can't be opened. For downloading, I used following code:

using System.Diagnostics;
using Windows.Networking.BackgroundTransfer;
using Windows.Storage;

private async void Button_Click(object sender, RoutedEventArgs e)
{
    try
    {
        Uri source = new Uri("http://www.sachsen.schule/~goethe-gym-auerbach/vplan/VertretungsplanMo.pdf");
        StorageFile destinationFile = await ApplicationData.Current.LocalFolder.CreateFileAsync("VertretungsplanMo.pdf", CreationCollisionOption.ReplaceExisting);                       
        BackgroundDownloader downloader = new BackgroundDownloader();
        DownloadOperation download = downloader.CreateDownload(source, destinationFile);
        Debug.WriteLine("Download successfull");
    }
    catch (Exception ex)
    {
        Debug.WriteLine("Download error. Exception: " + ex);
    }
}

Although I never get a download error, the file is always 0 KB.

Answer 1

you are forgetting to call download.StartAsync()

Beside that the BackgroundDownload api's are very powerful because it will make sure the files are downloaded also when the app is not running. But they are not that easy neither. So i recommend to use just the HttpClient for simplicity or check some samples with the backgrounddownloader.

See https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/BackgroundTransfer for more samples around background tranfser