Adding Encapsulation
The encapsulation example implements the clsPerson class and encapsulated
code, hiding the implementation code for all the properties and methods.
In the abstraction example, the user has to enter both their birthday and
age. As you encapsulate the implementation for the Person object, you will hide
the implementation of their age. Age will be derived from the person's birth
date, thus preventing a user from creating an invalid age and birth date values.
Properties are also encapsulated, allowing the class to derive the full name from
the first and last names that have been entered.
1. Add a new Windows Form item named "frmEncapsulation.vb".
2. Add the controls and parameters listed in Table 7- 5 to the frmEncapsulation.vb form.
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Table 7-5: Controls for the Form
Control Property Value
Button Name btnSubmit
Text Submit
Textbox Name txtFName
Textbox Name txtLName
Label Name lblFullNameDisplay
Textbox Name txtBirthDate
Label Name lblAgeDisplay
Textbox Name txtHoursWorked
Label Name lblTotalHoursWorked
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3. Create a new class in the Person class using the following code:
Public Class clsPerson2
Private m_FName As String
Private m_LName As String
Private m_BirthDate As Date
Private m_TotalHours As Integer
Public Property FName() As String
Get
Return m_FName
End Get
Set(ByVal Value As String)
m_FName = Value
End Set
End Property
Public Property LName() As String
Get
Return m_LName
End Get
Set(ByVal Value As String)
m_LName = Value
End Set
End Property
Public ReadOnly Property FullName() As String
Get
Return m_FName & " " & m_LName
End Get
End Property
Public Property BirthDate() As Date
Get
Return m_BirthDate
End Get
Set(ByVal Value As Date)
If IsDate(Value) Then
m_BirthDate = Value
End If
End Set
End Property
Public ReadOnly Property Age() As Integer
Get
If DatePart(DateInterval.Year, m_BirthDate) = 1 Then
Exit Property
End If
Return DateDiff(DateInterval.Year, m_BirthDate, Now)
End Get
End Property
'Method for adding hours to m_TotalHours worked.
Public Sub Work(ByVal intHours As Integer)
m_TotalHours += intHours
End Sub
Public ReadOnly Property TotalHoursWorked() As Integer
Get
Return m_TotalHours
End Get
End Property
End Class
4. Add the following object declaration to the initialization of frmAbstraction form:
' Here we are initializing the Person class. Normally this would be done
' when the class was needed for data access but in this case we are using
' the Person class to maintain our data.
Dim objPerson As New PersonProj.clsPerson2()
5. Right- click and select Properties then change the StartUp object to "frmEncapsulation".
6. Add the following code to the Submit button:
objPerson.FName = txtFName.Text
objPerson.LName = txtLName.Text
If IsDate(txtBirthDate.Text) Then
objPerson.BirthDate = CDate(txtBirthDate.Text)
Else
MsgBox("Please provide a valid Birth Date.")
End If
If IsNumeric(txtHoursWorked.Text) Then
objPerson.Work(CInt(txtHoursWorked.Text))
txtHoursWorked.Text = ""
End If
lblFullNameDisplay.Text = objPerson.FullName.ToString
lblAgeDisplay.Text = objPerson.Age.ToString
lblTotalHoursWorked.Text = "Total Hours Worked: " _
& objPerson.TotalHoursWorked.ToString
7. Now run the application and enter the information.
You'll notice that your age is calculated for you so that it cannot contradict
what the age should be based on the birth date, and the full name is derived
from the first and last name.
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