PRB: Some OLE Control Events Do Not Fire in Visual FoxPro 3.0b

ID: Q143303

3.00b WINDOWS kbinterop kbprb

The information in this article applies to:

Microsoft Visual FoxPro for Windows, version 3.0b

SYMPTOMS

Under certain circumstances, user code attached to events of OLE Controls may not execute. In particular, if you click a control while user code of another control is running, the OLE control seems to get the focus. However, the user code associated with the Click event is not called. This article explains why this behavior may happen.

CAUSE

Visual FoxPro regularly calls the Windows API PeekMessage to handle function keys and ON KEY LABEL. Calling PeekMessage yields Visual FoxPro processing and allows the OLE control to trigger the event. However, the firing of the event fails, and this behavior is not handled by the OLE control.

STATUS

This behavior is by design.

MORE INFORMATION

In xBase a user has the ability to assign commands to Hot-Keys, or ON KEY LABEL (OKL).The command associated with OKLs is called as soon as the key is pressed, no matter what is happening in Visual FoxPro. In the following example program, pressing the F5 key stops the execution of the program and immediately calls the statement assigned to the OKL. Once the OKL command is completed, Visual FoxPro resumes the program.

   ON KEY LABEL F5 ?MESSAGEBOX("Hello World")

   FOR i = 1 TO 1000000
   ENDFOR

To support this behavior, Visual FoxPro calls the Application Program Interface (API) PeekMessage() between each execution of a command. In the previous case, Visual FoxPro calls PeekMessage between the FOR command and the ENDFOR command. Visual FoxPro also calls PeekMessage() when it is executing a query or indexing a big table because users may press the ESC key to interrupt and halt the command. If Visual FoxPro didn't call PeekMessage, it wouldn't see the key until it's too late.

Calling PeekMessage yields Visual FoxPro processing and gives an OLE control a chance to look at its message queue and trigger events. However, at that time, Visual FoxPro does not handle the firing of an event because it is looking for key messages that are defined with OKLs. Visual FoxPro thus fails the firing of the control event.

Visual FoxPro fails the firing of the event in two different situations.

1. Visual FoxPro is currently handling an event. As Visual FoxPro begins

   to handle an event, it calls the FreezeEvents method on the OLE control
   that fired the event. Once the event has been handled, Visual FoxPro
   indicates that the container is accepting events from the control.

2. Visual FoxPro sees that the event was fired while it was executing

   user code (the FOR loop above.) At this point, Visual FoxPro tells the
   control that it failed the event but it does not call the FreezeEvents
   method.

   Visual FoxPro does not inform the control when to activate the event.
   So, if an event fails while Visual FoxPro is executing user code, the
   OLE control that placed the event in a queue cannot refire the event.

Steps to Reproduce Behavior

1. Create a new form.

2. Place an OLE Container control on the form. When the Insert object

   dialog box appears, follow these steps:

   a. Click Insert control.
   b. In the Control Type list box, click Outline control.

3. Place the following code in the Init event of the OLE control:

   THIS.Additem('Apples')
   THIS.Additem('Oranges')
   THIS.Additem('Bananas')
   THIS.Additem('Lemons')
   THIS.Indent(2)=2

4. Place the following code in the MouseDown and the Click events:

   *MouseDown
   =MESSAGEBOX("This is the MouseDown event")

   *Click
   =MESSAGEBOX("This is the Click event")

5. Place a command button on the form, and in its Click event, type:

   ACTIVATE SCREEN
   FOR i=1 TO 1000
   ?i
   ENDFOR

6. Save the form, and run it. When the window appears, click the command

   button. While the FOR loop is running, click the word Oranges in the
   Outline control. It appears as though the Outline is getting the focus,
   but the code associated with the Click event is not executed.

KBCategory: kbinterop kbprb KBSubcategory: FxinteropOle Additional reference words: 3.00b ActiveX OCX

Keywords          : FxinteropOle 
Version           : 3.00b
Platform          : WINDOWS