PRB: IPF from UserControl with a User-Defined Validate Event

ID: Q217026

The information in this article applies to:

Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 6.0

SYMPTOMS

You have a control that contains:


event Validate(Cancel as Boolean)
event Change()

You get an Invalid Page Fault (IPF) when the control fires the Change event.

CAUSE

When you put a control on the Visual Basic form, Visual Basic creates an extended control that provides some extended properties. The extended control has several events reserved, such as:


event DragDrop(Source As Control, X As Single, Y As Single)
event DragOver(Source As Control, X As Single, Y As Single, State As Integer)
event GotFocus()
event LostFocus()
event Validate(Cancel As Boolean)

When a Visual Basic client tries to sink an event, the extended control's events and the control's events will be combined into the same vtable. However, if your control also defines a Validate event, Visual Basic cannot distinguish between them and considers them to be one, so that the vtable structure for the sink is incorrect.

Furthermore, if you define other events used in the extended control, you may get an error message when you try to load the control to your project. A typical error message would be: "xxx control could not be loaded."

RESOLUTION

Change the Validate event to another name, such as:


event ValidateData(Cancel as Boolean)

You can also use the same event name with a different argument list, but then you cannot get to the event entry from the combo box in the integrated development environment (IDE).

MORE INFORMATION

Steps to Reproduce Behavior

Create a new ActiveX control project in Visual Basic. Change the project name to "MyOCX".

Add a CommandButton to the usercontrol.

Add the following code to the code window of the usercontrol:


Option Explicit
Event Validate(Cancel As Boolean)
Event Change()

Private Sub Command1_Click()
    RaiseEvent Change
End Sub

Compile the project, and it will be registered automatically. Close this project.

Create a new Standard EXE project. Form1 is created by default.

From the Project menu, select Components, select MyOCX from the list, and click OK. MyOCX is now available in the Toolbox.

Add a MyOCX control to Form1.

Add the following code to the code window of Form1.


Option Explicit

Private Sub UserControl11_Change()
    MsgBox "OK"
End Sub

Press the F5 key to run the project. Click CommandButton and you get an IPF.

Additional query words: GPF

Keywords : kbActivexEvents kbVBp600 kbGrpVB kbDSupport
Version : WINDOWS:6.0
Platform : WINDOWS
Issue type : kbprb