How to use WCF services in .netstandard with Xamarin.Forms project?

At the moment Xamarin apps aren't compatible with the Task-based asynchronous WCF proxy methods that the WCF Web Service Reference connected service provider generates for .NET Standard projects (bugzilla.xamarin.com Bug 51959).

One way to generate an older, compatible style of WCF proxy methods is to run SvcUtil.exe with the /async and /tcv:Version35 switches in a Developer Command Prompt. That will generate synchronous proxy methods, Begin/End style Asynchronous Programming Model (APM) callback proxy methods, and event-based proxy methods, all of which are compatible with Xamarin apps.

(Note: If you leave out the /async switch, SvcUtil.exe will generate the newer, incompatible Task-based proxy methods.)

Generate an older compatible style of WCF proxy methods via checked "Generate Synchronous Operations" checkbox on Configure WCF Web Service Reference screen:

Consume the web service:

KimlikServiceReference.KPSPublicSoapClient soapClient = new KimlikServiceReference.KPSPublicSoapClient(KimlikServiceReference.KPSPublicSoapClient.EndpointConfiguration.KPSPublicSoap);
//KimlikServiceReference.TCKimlikNoDogrulaResponse response = soapClient.TCKimlikNoDogrulaAsync(TCKimlikNo, Ad, Soyad, DogumYili).Result;
bool result = soapClient.TCKimlikNoDogrula(TCKimlikNo, Ad, Soyad, DogumYili);