void BeginDownloadingImage(App app, NSIndexPath path)
{
// Queue the image to be downloaded. This task will execute
// as soon as the existing ones have finished.
byte[] data = null;
DownloadTask = DownloadTask.ContinueWith(prevTask => {
try {
UIApplication.SharedApplication.NetworkActivityIndicatorVisible = true;
using (var c = new GzipWebClient())
data = c.DownloadData(app.ImageUrl);
} finally {
UIApplication.SharedApplication.NetworkActivityIndicatorVisible = false;
}
});
// When the download task is finished, queue another task to update the UI.
// Note that this task will run only if the download is successful and it
// uses the CurrentSyncronisationContext, which on MonoTouch causes the task
// to be run on the main UI thread. This allows us to safely access the UI.
DownloadTask = DownloadTask.ContinueWith(t => {
// Load the image from the byte array.
app.Image = UIImage.LoadFromData(NSData.FromArray(data));
// Retrieve the cell which corresponds to the current App. If the cell is null, it means the user
// has already scrolled that app off-screen.
var cell = Controller.TableView.VisibleCells.Where(c => c.Tag == Controller.Apps.IndexOf(app)).FirstOrDefault();
if (cell != null)
{
cell.ImageView.Image = app.Image;
}
}, CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, TaskScheduler.FromCurrentSynchronizationContext());
}