1. Lesson 7. Events, Delegates, Generics.
Programming in C#
Lesson 7. Events, Delegates, Generics.

2. Delegates

3. What is a delegate?
A delegate is a type safe pointer to a method (or a chain of methods)
All delegates are classes that inherited from MulticastDelegate class
Delegates are useful in callback scenarios
Delegates are used in APM (Asynchronous Programming Model)
Delegates are the base of events

4. Declaring a delegate delegate keyword Name
Return value type Parameters (number and type)

5. Using a delegate

6. Using a delegate as a callback method

7. Using a delegate as a callback method

8. Delegates chaining

9. Delegates chaining

10. Using delegates in APM

11. Anonymous Methods and Lambda Expressions

12. Events
Events provide a way for an object to be notified about something that has happened in another object

13. Designing a Type That Exposes an Event
Define a type that will hold any additional information that should be sent to subscribers
Define the event member (based on existing or custom delegate)
Define a method responsible for raising the event
Call the method responsible for raising the event from the appropriate place

14. Defining a type that will hold additional information

15. Defining the event member

16. Defining a method responsible for raising the event

17. Calling the method responsible for raising the event

18. Subscribing/Unsubscribing to events

19. Method GetInvocationList
Method GetInvocationList allows us to iterate manually through the list of subscribers and handle them correspondingly:

20. EventHandler and EventHandler<TEventArgs> delegates
In order to avoid the necessity to create custom delegates each time we need to expose an event, these standard delegates should be used:

21. Generics

22. What are generics?
Generics provide another form of code reuse: algorithm reuse
Generics allow us to encapsulate an algorithm within a class, interface or method without specifying the data type(s) that class or method works on
Generics provide type safety
Generics provide better performance (especially for collection data structures) as they prevent the necessity of boxing/unboxing and type casting
There are generic classes, interfaces, methods and delegates

23. A generic class sample

24. Operator default
Operator default specifies the default value of the type parameter. This will be null for reference types and zero for value types

25. Constraints on Type Parameters
where T: struct – The type argument must be a value type
where T: class – The type argument must be a reference type
where T: new() – The type argument must have a public parameterless constructor
where T: <base class name> – The type argument must be or derive from the specified base class
where T: <interface name> – The type argument must be or implement the specified interface

26. Generic Class with Constraints Sample

27. Generic Method with Constraints Sample