Visual Basic.NET How to Program (PDF)

Appendix G COM Integration 1339
Performance Tip G.1
The .NET and COM architectures are fundamentally different in terms of memory management
and object representation. Method calls to COM objects can degrade program performance,
because the RCW must convert all data types between the managed (.NET) context
and the unmanaged (COM) context. G.1
When we instantiate a COM object in Visual Basic, we are actually creating a new
instance of the object’s RCW. The communication between the RCW and the COM component
is entirely transparent, enabling the .NET developer to interact with the COM object
as if it were a .NET object.
We created an application (Fig. G.6) demonstrating how to use the Simple Addition
DLL that we want to integrate into .NET. This program includes three text boxes and a button.
After entering an Integer into each of the first two text boxes, the user clicks the Calculate
button, and the program displays the sum of the two Integers in the third text box.
1 ' Fig. G.6 : Addition.vb
2 ' COM component integration example.
3
4 Imports System.Windows.Forms
5
6 ' adds two numbers entered in text boxes
7 Public Class CAddition
8 Inherits System.Windows.Forms.Form
9
10 Dim firstInteger As Integer
11 Dim secondInteger As Integer
12 Dim total As Integer
13 Dim additionObject As Deitel_DLL.CAddition = _
14 New Deitel_DLL.CAddition()
15
16 Friend WithEvents lblDisplay1 As Label
17 Friend WithEvents lblDisplay2 As Label
18
19 Friend WithEvents txtFirstBox As TextBox ' first integer box
20 Friend WithEvents txtSecondBox As TextBox ' second integer box
21 Friend WithEvents txtResultBox As TextBox ' result text box
22
23 Friend WithEvents cmdCalculate As Button ' calculate value
24
25 ' Visual Studio .NET generated code.
26
27 ' event handler that enables cmdCalculate
28 Private Sub txtSecondBox_TextChanged( _
29 ByVal sender As System.Object, _
30 ByVal e As System.EventArgs) _
31 Handles txtSecondBox.TextChanged, _
32 txtFirstBox.TextChanged
33
34 ' enable button if text boxes contain text
35 If (txtFirstBox.Text "" AndAlso _
36 txtSecondBox.Text "") Then
Fig. G.6 COM DLL component in Visual Basic.NET (part 1 of 2).