Using Channel Factories in .NET framework

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Listing 36 Using Channel Factories
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3: Channels
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Listing 36 continued
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Two classes refer to channel factories within WCF: and They might seem similar, but they are actually separate class is used in classes that do different things The advanced situations where multiple clients need to be created Essentially , but it does not have any responsiit works with a given class is used by bilities for creating a channel stack The type Listing 37 shows de ning the class with a speci c class to call a service that implean example of using the interface ments the
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Be careful when implementing the statement to close the Listing 37 shows a best practice of having a around the service call so that any errors from the service , any exceptions would are known If we didn t have this bubble up through the using At that point the channel factory would throw an exception because it is closed This would mask the previous blocks so that error raised from the service call We use two we can catch any errors from the service calls
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Listing 37 Using
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The interface (see Listing 38) is the basis of all communication objects (channels, channel factories, channel listeners, and so
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3: Channels
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on) within WCF Developers who are planning to build custom channels or work with channels directly need to know this interface Communication objects within WCF need to implement a speci c state machine The state machine represents the state that all communication objects go through This approach is similar to what other communication objects (for example, sockets) go through The purpose of the interface (and its associated methods, states, and events) is to implement that state machine This allows WCF to treat all communication objects the same and abstracts away their underlying implementations
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Listing 38 Interface
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Listing 39 shows the states provided by the meration
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Listing 39 Enumeration
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The enumeration lists six states that communication objects go through The initial state for all communication objects is This is the state that communication objects are in when they are Along instantiated The nal state for all communication objects is interface that the way, methods are called on the transitions the communication object from one state to the next For exammethod is called to transition a communication object from ple, the state to the state Figure 35 shows a state diagram the showing the states and state transitions that a communication object goes through
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Abort() Abort() Abort()
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Close() or Abort() Closing Closed
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Abort()
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state diagram
One example of a communication object is the class, which is the base implementation for clients generated from Add Service Reference from Visual Studio or
3: Channels
NOTE
Cannot Reuse Clients
There is no going back after a communication object has transitioned state to either the or state This from the state means that the communication state cannot go back to the without rst re-creating the communication object Therefore, clients need to be re-created after they are closed (that is, when they are in the state)
Five events ( ported by the notify code of state transitions
) are supinterface These events are used to
Client Notifications
It is common for applications to maintain a reference to a client proxy In these situations it is important to use the state transitions events to state (and evenbe noti ed when the client proxy enters the state) so that communication between client and tually the server can be maintained
The interface is typically used by casting an existing communication object to the interface to gain access to the methods exposes However, at other and events that the times you want to create a new communication object that extends the capabilities of WCF In this situation, WCF has provided an abstract base which provides an implementation of class called interface and the associated state machine Listthe that was generated from ing 310 shows a This client inherits from the class The code interface so that shows the client being cast to an we can receive communication events