1. Events, Delegates, and LambdasC#

2. Role of Events, Delegates, and Event Handlers
Role of Delegates
Role of Event Handlers

3. Events, Delegats, and Event Handlers
EventArgs
Events, Delegats, and Event Handlers
Event Raiser
Delegate

4. Role of Events
To pull bints, right?

5. Events, Delegats, and Event Handlers
Event Raiser

6. What is an Event? Events are notifications
Play a central role in .NET framework
Provide a way to trigger notifications from end users or from objects.
Click Event
Button
Events signal the occurrence of an action/notification.
Objects that raise events don’t need to explicitly know the object that will handle the event. (You can have multiple handlers)

7. Role of Delegates
As real as it gets..

8. The Glue
Delegate
Between the Event Raiser and the Event Handler

9. What is a delegate? Specialized class often called a Function Pointer.
The glue/pipeline between an event and an event handler.
Based on MulticastDelegate base class.
Tracks all the listeners, in an Invocation list.

10. Delegates are a Pipeline
Event Handler
Delegates are a Pipeline
Delegate
EventArgs
Event

11. An event is useless without a delegate

12. Role of Event Handlers
Are you listening?

13. Event Handler
EventArgs
Event Handler

14. What is an Event Handler?
Responsible for receiving and processing data from a delegate.
Normally receives two paramters:
Sender
EventArgs
EventArgs responsible for encapsulating event data.

15. Role of EventHandler Event Handler
public void ButtonClick(object sender, EventArgs e) {
// Handling of button click occurs here }

16. Basic Delegate Demo
Simple demo to show how you can define and use delegates.

17. Custom Delegates
Where the fun begins!

18. Delegates can stand on their own.
No need for EventHandler or EventArgs.
You don’t have to use delegates with events.

19. Creating Delegates
Custom delegates are defined using the keyword delegate.

20. Creating Delegates int WorkType Handler Method Delegate
Delegate data from point A to point B.

21. Delegate Base Classes
Method – name of method where pipeline is dumping data
Target – object instance of where method resides
MulticastDelegate – a way to hold multiple delegates (multiple pipelines)
You cant inherit from Delegate or MulticastDelegate. You have to use the delegate keyword.

22. What is a Multicast Delegate?
Can reference more than one delegate function. (just a list of pipelines)
Tracks delegate references using an invocation list.
Delegates in the list are invoked sequentially.

23. Creating a delegate instance

24. Invoking a Delegate Instance

25. Adding to the Invocation List
With one call I can instantly notify multiple handlers!

26. Invocation List Demo

27. Events
Do we even need them?

28. Events

29. Defining an Event Can be defined using the event keyword.
Delegate
Friendly wrapper for delegate.

30. Raising Events Events are raised by calling the event like a method:
Need to check if there is anything in the Invocation List. If delegate is null behind the scenes you will get an exception. (Checks if any delegate is attached)
You can also just access the delegate directly:

31. Events Demo
Wow

32. EventArgs
The c# best practice for handling events

33. Creating custom EventArgs class
When custom data needs to be passed the EventArgs class can be extended.
Keeps signature clean.
If lots of data was needed to raised in event it can be encapsulated in inherited EventArgs object.

34. Using EventHandler<T>
.NET uses a generic EventHandler<T> class that can be used instead of a custom delegate:

35. Lambdas and delegates
Anonymous methods

36. Anonymous methods
Inline method.
Can get messy.

37. Event determines parameter types.
Lambdas
Event determines parameter types.
Inline Parameters
Lambda operator
A lambda is a concise inline method.
Compiler does a lot of magic for us.

38. Lambdas with custom delegate:

39. Lambdas Demo
Lana.. Lana… Lana.. … what? … Danger zone!

40. Action<T> and Func<T, TResult>
For the boyz..

41. Action<T>
The .NET framework provides several different out-of-the-box delegates that can save you a little bit of coding.
Action<T> accepts a parameter and returns no value.

42. Action<T>
The .NET framework provides several different out-of-the-box delegates that can save you a little bit of coding.
Action<T> accepts a parameter and returns no value.

43. Func<T, TResult>
Func<T, TResult> accepts a parameter and returns a value of type TResult.