Download image from server - image

Question

I've to download an image from the server on button click.
The code is:
private void Button_Click(object sender, RoutedEventArgs e)
{
(sender as Button).IsEnabled = false;
progressbar.IsIndeterminate = true;
WebClient w = new WebClient();
w.OpenReadAsync(new Uri("http://example.com/xxx/image.png"));
w.OpenReadCompleted += new OpenReadCompletedEventHandler(w_OpenReadCompleted);
}
void w_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
{
progressbar.IsIndeterminate = false;
BitmapImage b = new BitmapImage();
b.SetSource(e.Result);
Image img = new Image();
img.Source = b;
LayoutRoot.Children.Add(img);
}
The problem which I'm facing is that for the first time the data is being downloaded from the server and shown correctly. However, if I quit the application and again start it, it downloads the old image even if I have deleted the image from the server or changed the image. I think the image is getting cached somewhere but don't know how to solve this problem.

Answer 1

I think this will be the same as your issue:
How do you disable caching with WebClient and Windows Phone 7
I haven't noticed this behaviour when using the HttpWebRequest to get data. But I'am not sure about it.
Update: HttpWebRequest has by default the same behaviour but can be disabled. This blogpost is talking about the options you have:
http://www.nickharris.net/2010/10/windows-phone-7-httpwebrequest-returns-same-response-from-cache/

Answer 2

Finally managed to fix it.The only change that was made is:
w.OpenReadAsync(new Uri("http://example.com/xxx/image.png?q="+Guid.NewGuid()));

Answer 3

You could also use HttpWebRequest to download fresh data every request. Here is a simple class which sets up the asynchronous calls
Here is a simple http client which will download data from the given uri.
public static class HttpClient
{
public static void Execute(Uri uri, Action<HttpWebRequest> onrequest, Action<HttpWebResponse> onresponse)
{
var request = HttpWebRequest.CreateHttp(uri);
onrequest(request);
request.BeginGetResponse
(
result =>
{
try
{
if (request.HaveResponse)
onresponse((HttpWebResponse)request.EndGetResponse(result));
}
catch { }
},
null
);
}
}
Using the HttpClient with your button click event you get this
private void Button_Click(object sender, RoutedEventArgs e)
{
(sender as Button).IsEnabled = false;
progressbar.IsIndeterminate = true;
HttpClient.Execute
(
new Uri(http://example.com/xxx/image.png),
request =>
{
request.UserAgent = "Custom HTTP Client";
},
response =>
{
progressbar.IsIndeterminate = false;
BitmapImage b = new BitmapImage();
b.SetSource(response.GetResponseStream());
Image img = new Image();
img.Source = b;
LayoutRoot.Children.Add(img);
}
);
}