/// <summary>
/// Asynchronously downloads an image from the specified url
/// </summary>
/// <param name="url"></param>
/// <param name="callback">A <see cref="DownloadImageCompletedCallback"/> to be invoked when the request is completed</param>
/// <param name="userState">A state object to be returned to the callback</param>
/// <returns></returns>
public object DownloadImageAsync(string url, DownloadImageCompletedCallback callback, object userState)
{
string urlValidationError;
if (!IsValidURL(url, out urlValidationError))
{
throw new ArgumentException(urlValidationError);
}
ImageRequestAsyncState state = new ImageRequestAsyncState(callback, DownloadImageAsyncCompleted, userState);
HttpWebServiceRequest request = GetRequest();
request.GetResponseAsync(url, new MemoryStream(), IMAGE_ACCEPT, null, state);
return(request);
}
/// <summary>
/// Callback method for asynchronous requests
/// </summary>
private void DownloadImageAsyncCompleted(WebRequestAsyncState state)
{
ImageRequestAsyncState requestState = (ImageRequestAsyncState)state;
Image imageResult = null;
try
{
if (!requestState.Request.Cancelled && requestState.Error == null)
{
imageResult = GetImage(requestState.Request);
}
}
catch (HttpWebServiceException ex)
{
requestState.Error = ex;
if (requestState.Request.ResponseStream != null)
{
requestState.Request.ResponseStream.Close();
}
}
requestState.DownloadImageCompleted(new DownloadImageAsyncResult(imageResult, requestState.Error), requestState.UserState);
}
