PRB: TreeView Control HitTest Method Returns Empty String (168060)


The information in this article applies to:

  • Microsoft Visual FoxPro for Windows 5.0
  • Microsoft Visual FoxPro for Windows 5.0a
  • Microsoft Visual FoxPro for Windows 6.0
This article was previously published under Q168060

SYMPTOMS

The TreeView control that is contained within the COMCTL32.OCX, version 1.0.2908, returns NULL from the TreeView HitTest method when there is no Node at the specified coordinates. Version 5.00.3714 of the OCX returns an empty string in Visual FoxPro.

RESOLUTION

The best resolution to this is to disable ActiveX dual interface (VTABLE binding) support. Issue the =SYS(2333,0) command prior to the instantiation of the TreeView control. After the control is instantiated, ActiveX dual interface support can be turned back on if desired. See the SYS(2333) Online Help topic in Visual FoxPro for more information. Microsoft Technical Support has found that it is usually best to leave ActiveX dual interface support disabled.

If disabling the ActiveX dual interface support is not desired, the ISBLANK() function can be used in the TreeView HitTest method to return a NULL value. For example, =IIF(ISBLANK(xHitTest),.NULL.,xHitTest). See the More Information section below for an example of using this technique.

STATUS

Microsoft is researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Comctl32.ocx, version 1.0.2908, returns NULL in the TreeView HitTest method when there is no Node at the specified coordinates. Version 5.00.3714 returns an empty string. In Visual Basic, both versions of the OCX return nothing (NULL). Visual FoxPro appears to be handling the return value differently. The behavior occurs in both Visual FoxPro 5.0 and Visual FoxPro 5.0a. The newest version of the OCX ships with Visual FoxPro 5.0a. The following code illustrates the behavior: 
   =SYS(2333,1)                && to make sure VTABLE binding is on
   *=SYS(2333,0)               && as a test, unremark this and rerun code
   frmOLEForm=CREATEOBJECT('form')
   frmOLEForm.Show
   =MessageBox('In the next dialog box, choose the "Insert Control" '+ ;
      'button and then the "Microsoft TreeView Control" from the list.',0)
   frmOLEForm.AddObject('OLETree1','olecontrol')
   frmOLEForm.OLETree1.Visible = .T.
   =SYS(2333,1)                && this is optional

   ACTIVATE SCREEN

   xHitTest=frmOLEForm.OLETree1.HitTest(1,1)
   ? TYPE("xHitTest")
   ? IIF(ISBLANK(xHitTest), 'Empty', xHitTest)
   * The following is the workaround if VTABLE binding is not disabled
   ? IIF(ISBLANK(xHitTest), .NULL., xHitTest)
TYPE("xHitTest") should return "O" for object, because, according to the Help file, the HitTest method returns an object reference. In the newest version of the OCX and with ActiveX Dual Interface support enabled, xHitTest will return a Character type ("C") with a value of blank or "empty."
Modification Type:MajorLast Reviewed:8/13/1999
Keywords:KB168060
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