Xamarin.Forms中的HTTP请求

Question

I'm building a Xamarin.Forms App for Android and iOS which is supposed to consume an API. The API is kind of built in a REST spirit, I'm hosting the API on a local IIS Express server and my Android emulator has no problem finding it (tested on various endpoints and I can also display the api-doc). I'm trying to get in touch with a http://IPOfMyComputer/api/Stuffs endpoint which gives me a JSON list of Stuff. Using Postman I successfully get all the stuff I needed, a valid auth token in that case, to build a proper HTTP GET request. I'm using the Microsoft.Net.Http NuGet package to build this request as it seemed to be the proper tool to do the job. I'm doing this request building process in Xamarin.Forms "Main" project (not the iOS or Android one, the other one which I don't know how to name which is automatically by Visual Studio).

My code looks like this:

var rootUri = "http://IPOfMyComputer"
var requestedUri = "/api/Stuffs"
var client = new HttpClient();
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", 
"blablabla");
var response = await client.GetAsync(rootUri + requestedUri);

And this gives me an error "NotSupportedException" on the last instruction. I'm clueless here so some help would be really appreciated.
Edit
The proper error message is "System.InvalidCastException: Specified cast is not valid."

Answer 1

I found the source of that error:
Turns out it wasn't directly linked with the GetAsync method but with some mess in the code related with async/await use.
There was a bunch of crappy code everywhere. I dropped it all to go back to a regular MVVM logic and I put the async/await logic into methods invoked by eventhandlers (instead of trying to "create" an async builder for a class...).