Tuc Goodwin tgoodwin@ntpcug

1. Tuc Goodwin tgoodwin@ntpcug.org Sams Teach YourselfVisual C# 2010 in 24 HoursHour 3 : Understanding Classes and Object the C# Way

2. Agenda • Object and Component-Oriented Programming • Classes in C# • Scope and Accessibility • Methods and Properties • Nested and Partial Classes • Static Classes and Data • Object Initializers

3. Object and Component-Oriented Programming • A Class is a data structure that combines data storage with methods for manipulating the data. • Four primary OO concepts • Encapsulation • Abstraction • Inheritance • Polymorphism

4. Classes in C# • Define the body of a class with opening and closing curly braces { } • Scope – Where you declare a variable will determine who can see it. If you can see it, you can use it. • Declaration space – no two entities are allowed to have the same name

5. Scope and Accessibility

6. Try It Yourself Demo

7. Accessibility • Accessibility allows you to control visibility • Namespaces are not allowed to have any access modifiers. They are always public. • Classes default to internal, but are allowed to have either public or internal. • A nested class, a class defined inside of another class defaults to private accessibility • Class members default to private

8. Access Modifiers

9. “Black Diamond” • Best practice – Explicitly declaring accessibility indicates the choice was a conscious decision… i.e. self-documenting. • Be careful of “protected internal” because it is effectively one or the other. C# does not provide a concept of protected and internal.

10. Fields and Constants • Fields are variables that represented data associated with a class. Fields are private by default • Constants are immutable. They can be declared with access modifiers. They must be assigned a value as part of a declaration.

11. Try It Yourself Demo

12. Properties • A property provides a simple way to access a field. This allows for encapsulation, hiding the internal details of the field.

13. Automatic Properties

14. Declaring a Property

15. Declaring a Calculated Property

16. Read-Only and Write-Only Properties • How would you create a read-only property? • Remove the Set method leave only the Get method • How would you create a write-only property? • Remove the Getmethod leave only the Set method A simple mnemonic device: Get – “Gives” Set – “Receives”

17. Try It Yourself Demo

18. Methods • Methods (sometimes called functions) define and implement a behavior or action that can be performed.

19. Methods that returns a value • Methods can accept zero or more declared parameters

20. Parameters • Value parameters • Reference parameters – uses the ref keyword causes arguments to be passed by reference • Output parameters – uses the out keyword

21. Parameter Arrays • Parameter arrays are declared with the params keyword • A method’s formal parameter can include only a single parameter array • The parameter array must be the last parameter in the list of any parameter.

22. Overloaded Methods • …can vary only by signature. • … can vary only by the number and types of parameters • You can overload a method to have different return types, but you should avoid it to minimize the possibility for confusion…

23. Method Overloading

24. Try It Yourself Demo

25. Optional vs. Required Parameters • How do you specify an optional parameter? • A parameter with a default argument is an optional parameter • How do you specify a required parameter? • A parameter without a default argument is a required parameter

26. Instantiating a Class • You instantiate a class to create an instance Contact c = new Contact(); • A default constructor is the same name as the class and does not return a value.

27. Declaring a Constructor Overload

28. How does a class refer to itself? The this keyword

29. Chaining Constructors

30. Chaining Constructors

31. Nested Classes • A nested class is one that is fully enclosed, or nested, inside another class declaration • They have at least the same access level as the containing class.

32. Partial Classes • Partial classes enable you to split the declaration of a class into multiple parts, typically across multiple files. • Partial classes are implemented in the same way as a normal class but contain the keyword partial.

33. Static Classes • A static class can have only a static constructor • Static classes can not be instantiated, that is multiple instances cannot be created. • Typically used for utility or helper methods.

34. Extension Methods • Extension methods must be declared in a non-nested, non-generic static class. • An extension method defined in the same assembly as the type being extended

35. Try It Yourself Demo

36. Object Initializers • Suppose you want to instantiate and assign values as part of the constructor call? • This can be done by initializing the object at the same time.

37. Object Initializers example

38. Agenda • Object and Component-Oriented Programming • Classes in C# • Scope and Accessibility • Methods and Properties • Nested and Partial Classes • Static Classes and Data • Object Initializers

39. Questions?

40. Future Schedule