Calling an async api from a xamarin application - xamarin

Question

I am working on a xamarin mobile application, upon making an async call to the exposed api, i do not get any error, however when i execute the .Result on the task the call never proceeds and it stuck forever.
Click here to see stringResourceResponse details
The same .Result call from a separate project (windows service) in the same solution works.
Any idea if .NET standard is causing limitation in executing async tasks, any advice would be helpful, thanks
Code added below:
//This is code from app.xaml.cs
var stringResourceApi = new StringResourceApiTask();
Task.Run(() =>
{
a = controller.CallStringResourceApi(stringResourceApi);
}).Wait();
public class MobileController
{
public string CallStringResourceApi(StringResourceApiTask stringResourceApiTask)
{
return stringResourceApiTask.Start(StringResourceUrl);
}
}
public override string Start(string URL)
{
var stringResourceResponse = SendRequest(url, "", HttpMethod.Get);
var result = stringResourceResponse.Result;
return result;
}
protected async Task < string > SendRequest(string url, string uri, HttpMethod method, int attempt = 1, int maxAttempts = 5)
{
return await SendRequest(
url, uri, Key, Secret, method, string.Empty, attempt, maxAttempts)
.ConfigureAwait(false);
}
protected async Task<string> SendRequest(string url, string uri, string key, string secret, HttpMethod method,
string requestBody = "", int attempt = 1, int maxAttempts = 5)
{
if (attempt > maxAttempts)
{
return null;
}
var client = InitialiseHttpClient(key, secret);
var request = new HttpRequestMessage
{
RequestUri = string.IsNullOrEmpty(url) ? new Uri(uri) : new Uri(url),
Method = method,
};
if (!string.IsNullOrWhiteSpace(requestBody))
{
request.Content = new StringContent(requestBody, Encoding.UTF8, "application/json");
}
SetOutputText($"Attempting to communicate with {uri}...{Environment.NewLine}");
using (var response = await client.SendAsync(request).ConfigureAwait(false))
{
using (var content = response.Content)
{
try
{
response.EnsureSuccessStatusCode();
}
catch (HttpRequestException ex)
{
if (attempt > maxAttempts)
{
SetOutputText(errorMessage);
}
return await SendRequest(url, uri, key, secret, method, requestBody, attempt + 1).ConfigureAwait(false);
}
var responseBody = await content.ReadAsStringAsync().ConfigureAwait(false);
var isSuccessResponseButEmptyBody = response.IsSuccessStatusCode &&
(string.IsNullOrEmpty(responseBody) ||
string.IsNullOrWhiteSpace(responseBody));
if (!isSuccessResponseButEmptyBody)
{
return responseBody;
}
if (attempt > maxAttempts)
{
SetOutputText(errorMessage);
}
return await SendRequest(url, uri, key, secret, method, requestBody, attempt + 1).ConfigureAwait(false);
}
}
}

Answer 1

when i execute the .Result on the task the call never proceeds and it stuck forever.
Yes. This is a common deadlock situation. When code running on the UI thread blocks on asynchronous code, a deadlock usually occurs.
The same .Result call from a separate project (windows service) in the same solution works.
It works because the Win32 service code does not run on a UI thread.
The proper solution is to remove the blocking code; use await instead. This in turn will cause the calling methods to become async (e.g., StringResourceApiTask.Start), and they should also be awaited, etc. The usage of async and await should "grow" through your code; this is natural.
Alternatively, you can block in a thread pool thread, e.g., Task.Run(() => a = controller.CallStringResourceApi(stringResourceApi)).GetAwaiter().GetResult();. This is a bit of a hack (consuming an unnecessary thread), but it's a quick way to remove the deadlock. Note that this hack is not appropriate for ASP.NET apps; it's acceptable here since this is a UI app.