How To Use the CallByName Function to Run a Procedure

The CallByName function provides Visual Basic 6.0 with the ability to call a property or method of an object using a string at run-time. Unlike the previous versions of Visual Basic in which methods and properties had to be known at design-time, the CallByName function allows for a great deal of flexibility at run-time. The use of this function is limited to OLE servers and Visual Basic class modules.

The following sample demonstrates how to use the CallByName function to call a method, a Property Let, and a Property Get. For more information on the CallByName function, please refer to the Visual Basic Help Files and the Books On-Line.

Steps to Create Sample Project

1. Start a new Standard EXE project in Visual Basic. Form1 is created by default.
2. Add a Class Module (Class1) to the project.
3. Add the following code to the Class Module:

         Option Explicit
         Private MyPropValue As Integer
   
         Public Function Multiply(x As Integer, y As Integer) As Integer
            Multiply = x * y
         End Function
   
         Public Property Get MyProperty() As Variant
            MyProperty = MyPropValue
         End Property
   
         Public Property Let MyProperty(ByVal vNewValue As Variant)
            MyPropValue = vNewValue
         End Property
   
   						

4. Add the following code to the Form Module (Form1):

         Option Explicit
         Private Sub Form_Click()
            Dim myclass As New Class1
            Dim sum As Integer
            Dim prop As Integer
   
            ' Example of calling a method with CallByName
            ' equivalent to -- sum = myclass.Multiply(12, 12)
            sum = CallByName(myclass, "Multiply", VbMethod, 12, 12)
            MsgBox sum
   
            ' Example of a property let with CallByName
            ' equivalent to -- myclass.MyProperty = 5
            CallByName myclass, "MyProperty", VbLet, 5
   
            ' Example of a property get with CallByName
            ' equivalent to -- prop = myclass.MyProperty
            prop = CallByName(myclass, "MyProperty", VbGet)
            MsgBox prop
         End Sub
   
   						

5. Run the Project and click on Form1. A message box displaying the number 144 and a message box displaying the number 5 are shown in succession.