Visual Basic.NET How to Program (PDF)

Chapter 13 Graphical User Interfaces Concepts: Part 2 579
heritance. As we discussed in Chapter 9, Friend access modifiers allow access only
to other classes or modules belonging to the same assembly. In this example, FrmVisualTest
does not belong to the assembly of FrmInheritance (VisualForm), so
FrmVisualTest cannot modify the controls that it inherits from FrmInheritance.
1 ' Fig. 13.41: VisualTest.vb
2 ' A form that uses visual inheritance.
3
4 Public Class FrmVisualTest
5 Inherits VisualForm.FrmInheritance
6
7 ' new button added to form
8 Friend WithEvents cmdProgram As Button
9
10 ' Visual Studio .NET generated code
11
12 ' invoke when user clicks Learn the Program button
13 Private Sub cmdProgram_Click(ByVal sender As System.Object, _
14 ByVal e As System.EventArgs) Handles cmdProgram.Click
15
16 MessageBox.Show( _
17 "This program was created by Deitel & Associates", _
18 "Learn the Program", MessageBoxButtons.OK, _
19 MessageBoxIcon.Information)
20 End Sub ' cmdProgram_Click
21
22 End Class ' FrmVisualTest
Derived class
cannot modify
these controls.
Derived class
can modify
this control.
Fig. 13.41 Class FrmVisualTest, which inherits from class
VisualForm.FrmInheritance, contains an additional button.