// HOW-TO: Connect to an event source (IConnectionPoint)
public static void How_to_connect_to_an_event_source(IEngine engine)
{
// COM objects implement IConnectionPoint interface to make events
// they support available to clients. Working directly with this interface
// is possible but rather tedious. To facilitate working with events,
// the .NET Framework generates a set of helper classes when importing
// types information from a type library.
// For example, to subscribe to ICollectionEvents from an object, you use
// ICollectionEvents_Event helper class. Casting an object to this class
// will automatically check if the object implements IConnectionPoint interface
// and connect to ICollectionEvents if found. If the connection point is not available,
// the cast will result in a null:
trace("Cast the object to the helper class for the required event source.");
ICollectionEvents_Event collectionEvents = engine as ICollectionEvents_Event;
if (collectionEvents != null)
{
// IEngine does not support this kind of events, but if it did, we could
// assign a method to handle the events:
trace("Assign a method to be called when a particular event occurs.");
// collectionEvents.OnCollectionChanged +=
// new ICollectionEvents_OnCollectionChangedEventHandler( ... );
}
}
public void Dispose()
{
collectionEvents.OnCollectionChanged -= new ICollectionEvents_OnCollectionChangedEventHandler( collectionEvents_OnCollectionChanged );
collectionEvents = null;
}
public SampleCollectionEventsSink( object source, string _name )
{
// Check that the source object is a ICollectionEvents source (most collections are).
// Using the helper class generated by the framework which maps event source methods to delegates
collectionEvents = source as ICollectionEvents_Event;
assert( collectionEvents != null );
name = _name;
collectionEvents.OnCollectionChanged += new ICollectionEvents_OnCollectionChangedEventHandler( collectionEvents_OnCollectionChanged );
}
