WCF Web/ServiceHost - Singletons and initialisation

I have some Service class which is defined as InstanceContextMode.Single, and is well known in the hosting开发者_C百科 application. (The host creates an instance, and passes that to the WebServiceHost)

Hosting app:

WebServiceHost host = null;
SomeService serviceInstance = new SomeService("text", "more text");
host = new WebServiceHost(serviceInstance, baseUri);

Problem:

When I go to use the variables initialised when the service is created (ie, when a call is made to the service), they are either null or empty...

Am I wrong in assuming that as the instance being initialised in the hosting application is used for each request to the WebServiceHost?

Any pointers here would be great.

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Your assumption seems correct to me. Did you put the right code in the service constructor?