You are creating an application that consumes a Windows Communication Foundation (WCF) service.
The service implements the IService contract. The client application contains the CallbackHandler class, which implements IServiceCallback.
You need to ensure that a client proxy is created that can communicate with the service over a duplex channel.
Which code segment should you use?
A.
var handler = new CallbackHandler();
var clientFactory = new DuplexChannelFactory<IService>(new WSHttpContextBinding());
var client = clientFactory.CreateChannel(new InstanceContext(handler), new EndpointAddress(“…”));
B.
var handler = new CallbackHandler();
var clientFactory = new DuplexChannelFactory<IService>(typeof(CallbackHandler), new WSDualHttpBinding());
var client = clientFactory.CreateChannel(new InstanceContext(handler), new EndpointAddress(“…”));
C.
var handler = new CallbackHandler();
var clientFactory = new DuplexChannelFactory<IService>(new WSHttpBinding());
var client = clientFactory.CreateChannel(new InstanceContext(handler), new EndpointAddress (“…”));
D.
var handler = new CallbackHandler();
var clientFactory = new DuplexChannelFactory<IService>(typeof(CallbackHandler), new WSDualHttpBinding());
var client = clientFactory.CreateChannel(new EndpointAddress(“…”));
Explanation:
DuplexChannelFactory<TChannel> Class
(http://msdn.microsoft.com/en-us/library/ms576164(v=vs.90).aspx)
How do you know it’s not B?
why is the “handler” object created if it’s never used?
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Why B is not correct answer?
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It can’t be B because CreateChannel does not take InstanceContext as a parameter. So that only leaves D as the correct answer. See also: http://msdn.microsoft.com/en-us/library/ms576132.aspx
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Have to correct myself. The CreateChannel of DuplexChannelFactory has an overload
CreateChannel(InstanceContext, EndpointAddress) as described on http://msdn.microsoft.com/en-us/library/ms576164.aspx Then it would indeed make sense to choose B as the correct answer.
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Besides there is no CreateChannel of DuplexChannelFactory that takes just EndPointAddress argument, but there is one in the base class ChannelFactory.
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The question says “a client proxy is created that can communicate with the service over a duplex channel..”.
CreateChannel(InstanceContext, EndpointAddress) :Creates a duplex channel between a service and a callback instance on the client.
The correct answer is B.
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Just verifying that the correct answer should indeed be B.
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A
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