NSUrlSessionDataDelegate: Most methods don't get called - iis

Question

yesterday I wanted to implement the DidReceiveData method to my NSUrlSessionDataDelegate. I noticed that the DidReceiveData method never gets called, and while I tried to track down the error I noticed that the other methods don't get called either. I'm pretty sure that the other methods worked before, I don't know if I changed something or maybe a Xamarin.iOS update is the cause, but maybe I am wrong here and they never worked.
I can confirm this problem for the methods DidReceiveResponse, DidReceiveData, and DidCompleteWithError.
Here is the code that creates the NSUrlSession and handles the response (note: I call IIS WebMethods that answer in XML):
public async Task<string> Invoke(string sUrl)
{
session = NSUrlSession.FromConfiguration(NSUrlSessionConfiguration.DefaultSessionConfiguration,
(INSUrlSessionDelegate)new SessionDelegate((x)=> _fehlermeldung = x), // Übergebe Methode damit der SessionDelegate die Fehlermeldung weiterreichen kann
null);
request = CreateGETRequest(CreateNSUrl(sUrl));
var data = session.CreateDataTaskAsync(request, out dataTask);
dataTask.Resume();
NSUrlSessionDataTaskRequest response = null;
try
{
response = await data;
}
catch (NSErrorException ex)
{
throw new Exception(ex.Error.LocalizedDescription + ": " + _fehlermeldung);
}
var doc = new XmlDocument();
doc.LoadXml(response.Data.ToString());
XmlNode elem = doc.DocumentElement.FirstChild;
return elem.InnerText;
}
private NSUrl CreateNSUrl(string url)
{
string converted = ((NSString)url).CreateStringByAddingPercentEscapes(NSStringEncoding.UTF8);
var nsurl = NSUrl.FromString(converted);
if (nsurl == null)
throw new Exception("Fehlerhafte URL: Aus '" + url + "' konnte kein gültiges NSUrl Objekt erzeugt werden.");
return nsurl;
}
private NSMutableUrlRequest CreateGETRequest(NSUrl nsurl)
{
return new NSMutableUrlRequest(nsurl) { HttpMethod = "GET" };
}
And here is my implementation of the session delegate:
private class SessionDelegate : NSUrlSessionDataDelegate, INSUrlSessionDelegate
{
private readonly Action<string> setFehler;
public SessionDelegate(Action<string> setFehler)
{
this.setFehler = setFehler;
}
public override void DidReceiveResponse(NSUrlSession session, NSUrlSessionDataTask dataTask, NSUrlResponse response, Action<NSUrlSessionResponseDisposition> completionHandler)
{
var http_response = response as NSHttpUrlResponse;
if (http_response == null)
{
setFehler($"Keine HTTP Url Antwort erhalten: {Environment.NewLine}'{response}'");
completionHandler(NSUrlSessionResponseDisposition.Cancel);
return;
}
var status_code = (int)http_response.StatusCode;
if (status_code == 200)
{
completionHandler(NSUrlSessionResponseDisposition.Allow);
}
else
{
setFehler($"Verbindung abgewiesen, HTTP Status: { status_code}, '{ http_response.ToString()}'");
completionHandler(NSUrlSessionResponseDisposition.Cancel);
}
}
public override void DidReceiveData(NSUrlSession session, NSUrlSessionDataTask dataTask, NSData data)
{
// THIS DOES NOT GET CALLED :-(
}
public override void DidCompleteWithError(NSUrlSession session, NSUrlSessionTask task, NSError error)
{
if (error != null)
{
task.Cancel();
var ex = new NSErrorException(error);
throw (ex);
}
}
public override void DidReceiveChallenge(NSUrlSession session, NSUrlSessionTask task, NSUrlAuthenticationChallenge challenge, Action<NSUrlSessionAuthChallengeDisposition, NSUrlCredential> completionHandler)
{
[...] // This is working fine for Client Cert Authentication or Basic Authentication
}
}
The DidReceiveChallenge method does get called and is working. I cut it out for readability.
All the other methods don't get called. I would like to know what I am doing wrong. You can find the same questions from native iOS users, but I can't figure out how to implement their solutions with Xamarin.iOS.
Any help is appreciated, thanks in advance.