async load BitmapImage in C#

Question

I\'m trying to load a image asynchronously.

MainWindow code

public partial class MainWindow : Window
{
    private Data data = new D         


        

Answer 1

When a BitmapImage is created in a background thread, you have to make sure that it gets frozen before it is used in the UI thread.

You would have to load it yourself like this:

public static async Task<BitmapImage> GetNewImageAsync(Uri uri)
{
    BitmapImage bitmap = null;
    var httpClient = new HttpClient();

    using (var response = await httpClient.GetAsync(uri))
    {
        if (response.IsSuccessStatusCode)
        {
            using (var stream = new MemoryStream())
            {
                await response.Content.CopyToAsync(stream);
                stream.Seek(0, SeekOrigin.Begin);

                bitmap = new BitmapImage();
                bitmap.BeginInit();
                bitmap.CacheOption = BitmapCacheOption.OnLoad;
                bitmap.StreamSource = stream;
                bitmap.EndInit();
                bitmap.Freeze();
            }
        }
    }

    return bitmap;
}

Or shorter with BitmapFrame.Create, which returns an already frozen BitmapSource:

public static async Task<BitmapSource> GetNewImageAsync(Uri uri)
{
    BitmapSource bitmap = null;
    var httpClient = new HttpClient();

    using (var response = await httpClient.GetAsync(uri))
    {
        if (response.IsSuccessStatusCode)
        {
            using (var stream = new MemoryStream())
            {
                await response.Content.CopyToAsync(stream);
                stream.Seek(0, SeekOrigin.Begin);

                bitmap = BitmapFrame.Create(
                    stream, BitmapCreateOptions.None, BitmapCacheOption.OnLoad);
            }
        }
    }

    return bitmap;
}

Note that the second method requires to change the type of your Image property to BitmapSource (or even better, ImageSource), which would provide greater flexibility anyway.

---

An alternative method without any manual download might look like shown below. It also does not require to freeze the BitmatImage, because it is not created in a Task thread.

public static Task<BitmapSource> GetNewImageAsync(Uri uri)
{
    var tcs = new TaskCompletionSource<BitmapSource>();
    var bitmap = new BitmapImage(uri);

    if (bitmap.IsDownloading)
    {
        bitmap.DownloadCompleted += (s, e) => tcs.SetResult(bitmap);
        bitmap.DownloadFailed += (s, e) => tcs.SetException(e.ErrorException);
    }
    else
    {
        tcs.SetResult(bitmap);
    }

    return tcs.Task;
}