HOWTO: Use the OLE_OPTEXCLUSIVE Property Data Type

• Microsoft Visual Basic Control Creation, Learning, Professional, and Enterprise Editions for Windows, version 5.0

SUMMARY

An ActiveX control property can be any valid data type, such as long or string. Visual Basic provides some special data types for ActiveX control properties, such as OLE_OPTEXCLUSIVE. This article demonstrates how to use the OLE_OPTEXCLUSIVE data type.

MORE INFORMATION

The OLE_OPTEXCLUSIVE data type is internally represented as a Boolean, with valid values True and False. However, what makes OLE_OPTEXCLUSIVE unique is that if several controls of this data type are placed within a container (such as a Frame or Form), only one member of the group will be capable of being set to True, all others will be set to False.

For example, you could use an OLE_OPTEXCLUSIVE control if you created a option group with three options (Paper, Scissors, and Rock), where users can only select one of the three choices. Basically, when controls of this type are placed into a container, they are expected to behave as an option button; no more than one control can have its value set to True at any given time.

The steps below describe how to create a simple ActiveX control of type OLE_OPTEXCLUSIVE.

Create ActiveX Control

The following steps describe how to create an ActiveX control whose default value will be of type OLE_OPTEXCLUSIVE. If its default value is set to True, its color turns green. If its default value is set to False, its color turns red.

1. In Visual Basic 5.0, create a new ActiveX Control project.

2. From the Project menu, choose Project1 Properties. In the Project Name field, type "OptExclusiveControl" without the quotes. Click OK.

3. Set the UserControl BackColor property to red (&H000000FF&); this will be the default color for the UserControl.

4. View the code for the UserControl and copy the following code:

         Option Explicit
         Private CurrentValue As OLE_OPTEXCLUSIVE
   

         Private Sub UserControl_InitProperties()
            'Set the initial value for the Value property to False...much
            'like an option button would set its initial value to False
            '(unselected).
   
            Me.Value = False
   
         End Sub
   
         Private Sub UserControl_Click()
            'When the User Clicks on the control, the Value property of the
            'control will be set to True, just as an option button
            'sets its value to True when it is clicked.
   
            Me.Value = True
   
         End Sub
   
         Public Property Get Value() As OLE_OPTEXCLUSIVE
            'Retrieve the current value of the Value property
   
            Value = CurrentValue
   
         End Property
   
         Public Property Let Value(ByVal NewValue As OLE_OPTEXCLUSIVE)
            'If the NewValue is True, the UserControls color is set
            'to green and all other instances of the control within
            'a container are set to False automatically.
            '
            'If NewValue is False, the UserControls color is set to red.
   
            If NewValue = True Then
               UserControl.BackColor = &HFF00&   'Green
               CurrentValue = NewValue
               PropertyChanged "Value"   'Notifies the container that the
                                         'property has changed. If you exclude
                                         'this line of code, the ActiveX
                                         'control will not behave as an
                                         'option group because there is no
                                         'mechanism to inform the container
                                         'that the property has changed.
               Else
                  UserControl.BackColor = &HFF&     'Red
                  CurrentValue = NewValue
                  PropertyChanged "Value"
               End If
            End Property
   
   

5. From the Tools menu, choose Procedure Attributes.

6. In the Procedure Attributes window, be sure the Value property is selected in the Name combo box, and then click Advanced.

7. For Procedure ID, choose (Default) from the drop -own list. Only one property procedure can be set to the default. This becomes the default property for your ActiveX Control. If you do not set the OLE_OPTEXCLUSIVE property to the default value, it will not function as expected. In this example, the property was named "Value" for simplicity. However, you can set any named property procedure as your default.

8. Save the Project and compile the OptExclusiveControl.Ocx.

   You now have an ActiveX Control whose data type is OLE_OPTEXCLUSIVE. The next set of steps describe how to build a container to test the control.

Creating the Test Container

The test container is designed to test the OptExclusiveControl created in the steps above.

1. Create a new Standard EXE project in Visual Basic 5.0. Form1 is created by default.

2. From the Project menu, choose Components. Select the OptExclusiveControl created in the above steps.

3. Add a Frame control to Form1.

4. Add three OptExclusiveControls to the Frame.

5. Run the Project.

   When the project is running, Form1 will display the frame with three of the OptExlcusiveControls on it. Clicking on a OptExclusiveControl turns its color green. As you click on the other OptExlcusiveControls, notice that only one OptExclusiveControl can be green at any given time.

Keywords          : vb5all vb5howto
Version           : WINDOWS:5.0
Platform          : WINDOWS
Issue type        : kbhowto