在Windows 8中下载并显示图像

Question

I have the following code for downloading an image from a webserver:

private async void Test_Click(object sender, RoutedEventArgs e)
{
    HttpClient httpClient = new HttpClient();

    HttpRequestMessage request = new HttpRequestMessage(
      HttpMethod.Get, "http://www.reignofcomputer.com/imgdump/sample.png");

    HttpResponseMessage response = await httpClient.SendAsync(request,
        HttpCompletionOption.ResponseHeadersRead);

    var imageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(
        "sample.png", CreationCollisionOption.ReplaceExisting);

    var fs = await imageFile.OpenAsync(FileAccessMode.ReadWrite);
    DataWriter writer = new DataWriter(fs.GetOutputStreamAt(0));
    writer.WriteBytes(await response.Content.ReadAsByteArrayAsync());
    await writer.StoreAsync();
    writer.DetachStream();
    await fs.FlushAsync();

    displayImage();
}

private void displayImage()
{
    image1.Source = new BitmapImage(
        new Uri("ms-appdata:///local/sample.png", UriKind.Absolute));
}

When I run the code, the image fails to display despite appearing in the folder (at
C:\\Users\\User\\AppData\\Local\\Packages\\XXXXX\\LocalState).

If I run it again, I get a UnauthorizedAccessException was unhandled by user code , Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED)) Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED)) at CreateFileAsync .

Any ideas?

Answer 1

Here's a working sample of an app that downloads an image and displays it as the background of the app:

http://laurencemoroney.azurewebsites.net/?p=247

async void doLoadBG()
{
    System.Xml.Linq.XDocument xmlDoc = XDocument.Load(
     "http://www.bing.com/HPImageArchive.aspx?format=xml&idx=0&n=1&mkt=en-US");

    IEnumerable<string> strTest = from node in xmlDoc.Descendants("url")
        select node.Value;

    string strURL = "http://www.bing.com" + strTest.First();
    Uri source = new Uri(strURL);
    StorageFile destinationFile;

    try
    {
        destinationFile = await ApplicationData.Current.LocalFolder
            .CreateFileAsync(
              "downloadimage.jpg", CreationCollisionOption.GenerateUniqueName);
    }
    catch (FileNotFoundException ex)
    {
        return;
    }

    BackgroundDownloader downloader = new BackgroundDownloader();

    DownloadOperation download =
        downloader.CreateDownload(source, destinationFile);

    await download.StartAsync();
    ResponseInformation response = download.GetResponseInformation();
    Uri imageUri;
    BitmapImage image = null;

    if (Uri.TryCreate(destinationFile.Path, UriKind.RelativeOrAbsolute,
        out imageUri))
    {
        image = new BitmapImage(imageUri);
    }

    imgBrush.ImageSource = image;
}

Answer 2

If you don't want to download the image, you can just do this:

private void displayImage()
{
    image1.Source = new BitmapImage(
        new Uri("http://www.reignofcomputer.com/imgdump/sample.png"));
}

Does that help?