Programming Visual Basic 2005

Importing COM Components

Many of the COM components that companies develop are not ActiveX Controls; they are standard COM dynamic link library (DLL ) files . To see how to use these with .NET, return to VB6 and create a COM business object that will act exactly as the component from the previous section did.

Tip

Once again, if you don't have VB6, you can download the DLL as explained earlier.

The first step is to create a new ActiveX DLL project. This is how VB6 creates standard COM DLLs. Name the class ComCalc and name the project ComCalculator. Save the file and project. Copy the methods from Example 7-1 (shown here for your convenience in Example 7-3) into the code window.

Example 7-3. Methods for VB6 COM DLL ComCalc

Public Function _
Add(left As Double, right As Double) _
As Double
    Add = left + right
End Function

Public Function _
Subtract(left As Double, right As Double) _
As Double
    Subtract = left - right
End Function

Public Function _
Multiply(left As Double, right As Double) _
As Double
    Multiply = left * right
End Function

Public Function _
Divide(left As Double, right As Double) _
As Double
    Divide = left / right
End Function

Integrating the COM DLL into .NET

Create a new form called frmCOMDLL. Add a menu choice to the Fun menu on the Welcome form that invokes that form.

Now that you have created the ComCalc DLL, you can import it into .NET. Before you can import it, however, you must choose between early and late binding. When the client calls a method on the server, the address ...