C# 4 and .NET 4

summary ❘ 205
}
}
public void NewCarIsHere(object sender, CarInfoEventArgs e)
{
Console.WriteLine("{0}: car {1} is new", name, e.Car);
}
bool IWeakEventListener.ReceiveWeakEvent(Type managerType, object sender,
EventArgs e)
{
NewCarIsHere(sender, e as CarInfoEventArgs);
return true;
}
code snippet WeakEventsSample/Consumer.cs
Inside the Main method where the publisher and listeners are connected, the connection is now done
by using the static AddListener() and RemoveListener() methods from the WeakCarInfoEvent
Manager class.
static void Main()
{
var dealer = new CarDealer();
var michael = new Consumer("Michael");
WeakCarInfoEventManager.AddListener(dealer, michael);
dealer.NewCar("Mercedes");
var nick = new Consumer("Nick");
WeakCarInfoEventManager.AddListener(dealer, nick);
dealer.NewCar("Ferrari");
WeakCarInfoEventManager.RemoveListener(dealer, michael);
}
dealer.NewCar("Toyota");
code snippet WeakEventsSample/Program.cs
With this additional work of implementing the weak event pattern, the publisher and listeners are no longer
strongly connected. When a listener is not referenced anymore, it can be garbage collected.
summary
This chapter gave you the basics of delegates, Lambda expressions, and events. You learned how to declare
a delegate and add methods to the delegate list. You learned how to implement methods called by delegates
with Lambda expressions. You also learned the process of declaring event handlers to respond to an event,
as well as how to create a custom event and use the patterns for raising the event.
As a .NET developer, you will be using delegates and events extensively, especially when developing
Windows applications. Events are the means that the .NET developer has to monitor the various Windows
messages that occur while the application is executing. Otherwise, you would have to monitor the WndProc
and catch the WM_MOUSEDOWN message instead of getting the mouse Click event for a button.
The use of delegates and events in the design of a large application can reduce dependencies and the
coupling of layers. This allows you to develop components that have a higher reusability factor.
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