Microsoft Lync 2010 API features you add to your client application depend on a reliable network connection to send and receive the SIP messages that are the basis of collaboration between two Microsoft Lync Server 2010 clients. Virtually every method you call on a Lync 2010 API class results in a SIP request being sent from your client over a network to Lync Server 2010. Even the best network topology occasionally exhibits a latency that prevents an instantaneous response to a client's SIP request. To avoid blocking code execution during an asynchronous network operation, Lync 2010 API supports the standard .NET asynchronous programming pattern. For information about the asynchronous programming pattern used with Lync 2010 API, see Calling Synchronous Methods Asynchronously
Lync API Asynchronous Programming Pattern
The Lync 2010 API asynchronous programming pattern has three elements.
The IAsyncResultinterface. You must obtain an instance of this interface as a return value of a call into a Lync 2010 API method if you intend to block execution on your UI thread until an asynchronous operation completes. Otherwise, you obtain this interface as the parameter of a callback method conforming to the System.AsyncCallbacksignature.
The asynchronous callback method. This type of callback method requires that you instantiate a System.AsyncCallback Delegatewith a method that you define.
The state change event handler. This is an asynchronous event callback method whose Lync 2010 API delegate defines the method signature. Unlike a System.AsyncCallbackmethod that is called only when an operation completes, a state changed event handler is called whenever the state of a Lync 2010 API class changes.
You must implement event handlers in order to respond to events that can be raised when the state of an Lync 2010 API object changes. A callback method is called whenever you define and pass your callback method to a Lync 2010 API asynchronous method as a delegate.
Callback methods are useful when you want to check on the status of an asynchronous operation your client has initiated. The callback method does not provide you with the new state of an object at the completion of an operation. To obtain the new state of an object, you must handle the event associated with the class instance whose method you call. A callback method is raised once when a local user invokes an asynchronous method.
The three elements of a callback are:
A Lync 2010 API delegate type.
A client defined callback method to be called by Lync 2010 API.
A state object defined on your client and passed by Lync 2010 API to your callback method.
You pass the callback method you have created with the signature of a specified callback delegate as a parameter of the asynchronous Lync 2010 API method you call. You can also declare an object that will hold any state value you choose to assign to the asynchronous operation. If you do not declare and pass an asynchronous state object, then you must pass a null value. The asynchronous state object is useful when you have declared a single System.AsyncCallbackmethod to be called upon completion of different kinds of operations. The state of the operation including the nature of the operation is available to the callback method upon execution.
IAsyncResultis passed into the EndXXX() method call that corresponds to the BeginXXX() call that started an asynchronous operation. If you intend to block your UI thread until an asynchronous operation completes, you must call EndXXX() on the same code path used for the BeginXXX() call. Otherwise, you call EndXXX() within your callback method. Where an asynchronous operation returns results such as a conversation window ( ) or contact search results ( ), you call EndXXX() to get the results.
If you are developing an application using Silverlight, you cannot use the IAsyncResult. AsyncWaitHandleproperty to signal your code that an asynchronous operation has completed. In this scenario, AsyncWaitHandlereturns null.
Lync API Events
Events are raised any time state changes on an object. State change on an object is not always the result of a local operation. Instead, the state change can be the result of an action by a remote user.
An event handler returns event source and data classes to your application logic as parameters. A source class instance is the object raising an event while a data class instance gives you related source state change values. You examine the data instance to see the original and new state of an object.
For example, undergoes a state change when a conversation invitation comes from a remote user. The incoming invitation invokes the event.
A instance undergoes a state change when notified that a remote user has published new or updated presence information. The notification of updated presence information invokes a event on the instance.
It is essential that your client listens for invitations by registering for appropriate events and listens for notifications from Lync Server 2010 by registering for appropriate notification-related events. To listen for Lync 2010 API events, your application must:
Create a set of callback method to act as event handlers for the events that will be raised by Lync 2010 API classes.
Register for a set of events on Lync 2010 API before calling methods on the interface that can raise events.
Handle events to get the state of the SIP request generated by the original asynchronous Lync 2010 API method call. Be prepared to handle both a successful or failed request. Most events raised should be handled. In many cases, you can update your user interface to inform the user of the status of a SIP request. For example, you should inform a user of the progress of a request to sign in to Lync Server 2010.