VB 4.0 Calls the FreezeEvents Method to Inform OLE Controls (129733)


The information in this article applies to:

  • Microsoft Visual Basic Standard Edition, 32-bit, for Windows 4.0
  • Microsoft Visual Basic Professional Edition, 16-bit, for Windows 4.0
  • Microsoft Visual Basic Professional Edition, 32-bit, for Windows 4.0
  • Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows 4.0
  • Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows 4.0
This article was previously published under Q129733

SUMMARY

Visual Basic version 4.0 uses the FreezeEvents method to inform an OLE control of its readiness to accept events at key points during execution.

MORE INFORMATION

This information is quoted from the OLE Control Developer's Kit, Part 4, Appendix D:

The FreezeEvents method determines whether the control should fire events. When initially created, the control's freeze count is at zero, and the control is free to fire events when appropriate. If the container calls FreezeEvents(TRUE), then the freeze count is incremented, and the control should not fire any events until the freeze count returns to zero by the container calling FreezeEvents(FALSE). This mechanism gives the container a way to suppress events being fired until it is fully ready to deal with them.

The control is free to decide whether to discard events triggered when the control is frozen, or to queue them up and fire them when the control becomes unfrozen. Normally, a control makes this decision based on how important the event is to the control's contract. If discarding the event is likely to break users' assumptions and therefore their code, then the control should queue the event.

Visual Basic uses the FreezeEvents at the following key points during run time:

  • Before starting to load a form, FreezeEvents(TRUE) is called on all existing controls. Any controls on the form being loaded will have FreezeEvents(TRUE) called immediately before their SetClientSite is called. FreezeEvents(FALSE) is called on all controls immediately after the Form_Load event is fired. This is to guarantee that Form_Load is the first event fired once a form is loaded.
  • Before dynamically loading a control, FreezeEvents(TRUE) is called on all existing controls. The control being dynamically loaded will have FreezeEvents(TRUE) called immediately before its SetClientSite is called. FreezeEvents(FALSE) is called on all controls after the new control is completely loaded.
  • FreezeEvents(TRUE) is called on all controls before a modal dialog or message box is put up. FreezeEvents(FALSE) is called after that dialog or messagebox is destroyed.
  • In design mode, whenever a control is first drawn on a form, its FreezeEvents(TRUE) is called immediately before its SetClientSite is called.
  • FreezeEvents(TRUE) is called on all controls whenever you exit run mode, whether transitioning to break or design mode. This is only interesting in the run-to-break transition in the design environment because in the run-to-design transition (or in built-EXEs), the controls are in the process of being destroyed.
  • FreezeEvents(FALSE) is called on all controls whenever you enter run mode from break mode. However, this doesn't apply to built EXEs.
Modification Type:MajorLast Reviewed:12/9/2003
Keywords:KB129733
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