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Objectives

1. Objectives. Define a class Add properties to a class Instantiate an object from a class that you define Add Property procedures to a class. Objectives ( continued ). Create constructors Add methods to a class Include data validation in a class. Classes and Objects.

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Objectives

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  2. Objectives • Define a class • Add properties to a class • Instantiate an object from a class that you define • Add Property procedures to a class Microsoft Visual Basic .NET: Reloaded

  3. Objectives (continued) • Create constructors • Add methods to a class • Include data validation in a class Microsoft Visual Basic .NET: Reloaded

  4. Classes and Objects • Object-oriented programs are based on objects, which are instantiated from classes • A class contains (encapsulates) the properties (attributes) that describe a person, place, or thing • Examples: Student, School, Book • An object is a specific instance of a class • Examples: “You” are a student that goes to a specific school and are using this specific book • VB has many built-in objects such as Textbox controls, Forms, and Labels Microsoft Visual Basic .NET: Reloaded

  5. Defining a Class • Use the Class statement • Begins with keyword Class and ends with End Class Microsoft Visual Basic .NET: Reloaded

  6. HOW TO… Microsoft Visual Basic .NET: Reloaded

  7. Defining a Class (continued) Microsoft Visual Basic .NET: Reloaded

  8. Defining a Class (continued) Microsoft Visual Basic .NET: Reloaded

  9. HOW TO… Microsoft Visual Basic .NET: Reloaded

  10. Example 1 – Using a Class that Contains Properties Only • Assume that the sales manager at Sweets Unlimited wants an application that allows him to save each salesperson’s • name • quarterly sales amount • quarterly bonus amount in a sequential access file • The bonus amount is calculated by multiplying the sales amount by 5% Microsoft Visual Basic .NET: Reloaded

  11. Example 1 – Using a Class that Contains Properties Only (continued) • Figure 11.6 shows a sample run of the Sweets Unlimited application Microsoft Visual Basic .NET: Reloaded

  12. Example 1 – Using a Class that Contains Properties Only(continued) • Figure 11.7 shows the Salesperson class defined in the Salesperson.vb file Microsoft Visual Basic .NET: Reloaded

  13. Example 1 – Using a Class that Contains Properties Only(continued) Microsoft Visual Basic .NET: Reloaded

  14. Example 1 – Using a Class that Contains Properties Only(continued) Microsoft Visual Basic .NET: Reloaded

  15. Example 2 – Using a Class that Contains Properties and Methods • Create a class named Square and then use in the Area application • Square class creates an object that can calculate and return the area of a square, using side measurement provided by application • Figure 11.9 shows a sample run of the Area application • Figure 11.10 shows the Square class defined in the Square.vb file Microsoft Visual Basic .NET: Reloaded

  16. Example 2 – Using a Class that Contains Properties and Methods(continued) Microsoft Visual Basic .NET: Reloaded

  17. Example 2 – Using a Class that Contains Properties and Methods (continued) Microsoft Visual Basic .NET: Reloaded

  18. Example 2 – Using a Class that Contains Properties and Methods (continued) • Creating a Public Property • Declare a class-level private variable to hold the value to be stored by the property • Data type of property and private variable must match each other • Heading begins with keywords Public Property Microsoft Visual Basic .NET: Reloaded

  19. Example 2 – Using a Class that Contains Properties and Methods (continued) • Code Get block to retrieve contents of private variable • Code Set block to change contents of private variable • Ends with keywords End Property Microsoft Visual Basic .NET: Reloaded

  20. HOW TO… Microsoft Visual Basic .NET: Reloaded

  21. Constructors • Constructor method whose instructions the computer processes, automatically, each time an object is created (instantiated) from the class • Constructor begins with Public Sub New followed by a set of optional parameters • Parameter list may be empty - New() • No parameters is called “default constructor” • Every class should have at least one constructor and may have several Microsoft Visual Basic .NET: Reloaded

  22. HOW TO… Microsoft Visual Basic .NET: Reloaded

  23. Methods Other Than Constructors • Sub methods do not return a value • Function methods return a value to the calling procedure Microsoft Visual Basic .NET: Reloaded

  24. Methods Other Than Constructors(continued) Microsoft Visual Basic .NET: Reloaded

  25. Example 3 – Using a Class that contains two Constructors and Data Validation • Create a class named MyDate and then use in the Personnel application • MyDate class creates an object that returns a month number, followed by a slash, and a day number • Figure 11.15 shows a sample run of the Personnel application • Figure 11.16 shows the MyDate class defined in the MyDate.vb file Microsoft Visual Basic .NET: Reloaded

  26. Example 3 – Using a Class that contains two Constructors and Data Validation (continued) Microsoft Visual Basic .NET: Reloaded

  27. Example 3 – Using a Class that contains two Constructors and Data Validation (continued) Microsoft Visual Basic .NET: Reloaded

  28. Example 3 – Using a Class that contains two Constructors and Data Validation (continued) Microsoft Visual Basic .NET: Reloaded

  29. Example 3 – Using a Class that contains two Constructors and Data Validation (continued) Microsoft Visual Basic .NET: Reloaded

  30. Programming Example – Kessler Landscaping Application • Monica Kessler, the owner of Kessler Landscaping, wants an application that she can use to estimate the cost of laying sod • Use a MyRectangle class in this application Microsoft Visual Basic .NET: Reloaded

  31. TOE Chart Microsoft Visual Basic .NET: Reloaded

  32. User Interface Microsoft Visual Basic .NET: Reloaded

  33. Objects, Properties, and Settings Microsoft Visual Basic .NET: Reloaded

  34. Tab Order Microsoft Visual Basic .NET: Reloaded

  35. Pseudocode btnExit Click event procedure 1. close application btnCalc Click event procedure 1. declare a MyRectangle object 2. assign the length and width to the MyRectangle object’s properties 3. assign the sod price to a variable 4. calculate the area of the rectangle 5. calculate the total price of the sod 6. display the total price of the sod in lblTotalPrice txtLength, txtWidth, and txtPrice TextChanged event procedures 1. clear the contents of the lblTotalPrice control Microsoft Visual Basic .NET: Reloaded

  36. Code (MyRectangle.vb file) Microsoft Visual Basic .NET: Reloaded

  37. Code (MyRectangle.vb file)(continued) Microsoft Visual Basic .NET: Reloaded

  38. Code (Kessler Form.vb file) Microsoft Visual Basic .NET: Reloaded

  39. Code (Kessler Form.vb file) (continued) Microsoft Visual Basic .NET: Reloaded

  40. Summary • The objects used in an object-oriented program are created, or instantiated, from classes • A class contains (encapsulates) the properties (attributes) that describe the object it creates, and the methods (behaviors) that allow the object to perform tasks • In Visual Basic .NET, you can create objects from classes that you define with the Class statement Microsoft Visual Basic .NET: Reloaded

  41. Summary (continued) • Good programming practice to enter Option Explicit On and Option Strict On statement in both the form file and class file • The first letter in the class name, as well as the first letter in any subsequent words in the name, should be capitalized • The properties in a class should be assigned a name composed of one or more words, with the first letter of each word being capitalized • You should use nouns and adjectives to name a property Microsoft Visual Basic .NET: Reloaded

  42. Summary (continued) • Methods in a class should be assigned a name composed of one or more words, with the first letter of each word being capitalized • You should use a verb for the first word in the name, and nouns and adjectives for any subsequent words in the name • Variables declared using the Public keyword in a class definition can be accessed by any application that uses an object created from the class • Most classes contain properties and methods Microsoft Visual Basic .NET: Reloaded

  43. Summary (continued) • When an application needs to assign data to or retrieve data from a Private variable in a class, it must use a Public property to do so • You create a Public property using a Property procedure • The Get block in a Property procedure allows an application to access the contents of the class’s Private variables • The Set block in a Property procedure allows an application to assign values to the class’s Private variables Microsoft Visual Basic .NET: Reloaded

  44. Summary (continued) • A class can have one or more constructors • All constructions are Sub procedures • The default constructor is automatically processed when an object is created from the class Microsoft Visual Basic .NET: Reloaded

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