Microsoft KB Archive/196219

= FIX: VB User Control AmbientChanged Event Does Not Fire in IE =

Article ID: 196219

Article Last Modified on 10/16/2002

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APPLIES TO


 * Microsoft Internet Explorer 3.0
 * Microsoft Internet Explorer 3.01
 * Microsoft Internet Explorer 3.02
 * Microsoft Internet Explorer 4.0 128-Bit Edition
 * Microsoft Internet Explorer 4.01 Service Pack 2
 * Microsoft Visual Basic 5.0 Professional Edition
 * Microsoft Visual Basic 6.0 Professional Edition
 * Microsoft Visual Basic 5.0 Enterprise Edition
 * Microsoft Visual Basic 6.0 Enterprise Edition

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This article was previously published under Q196219



SYMPTOMS
Visual Basic user controls that are hosted on an HTML page in Internet Explorer fail to fire the UserControl_AmbientChanged event, even when the ambient properties of the HTML container have clearly changed.



CAUSE
Internet Explorer always passes DISPID_UNKNOWN when calling the OnAmbientPropertyChanged method of the IOleControl interface. While legal according to the rules of this method, it forces controls to query the container back for each property of interest to determine which ambient properties changed.

Visual Basic 5.0 does not handle DISPID_UNKNOWN correctly in OnAmbientPropertyChanged and fails to fire the AmbientChanged event.



STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual Studio, 6.0.



Steps to reproduce behavior
 Create a new user control project in Visual Basic. Add two command buttons to the default form for the control.  Add the following code: Private Sub Command1_Click Parent.bgcolor = vbRed End Sub

Private Sub Command2_Click Parent.bgcolor = vbBlue End Sub

Private Sub UserControl_AmbientChanged(PropertyName As String) MsgBox "ambient changed" End Sub  Make the control.  Place the control on a Web page (make sure you replace the CLSID in the code below):  <HEAD><TITLE>Repro of DISPID_UNKNOWN AmbientChanged Bug</TITLE></HEAD> <BODY> <OBJECT ID="AmbientBugTest1" WIDTH=320 HEIGHT=240 CLASSID="CLSID:<Insert User Control's Class ID here.>"> <PARAM NAME="_ExtentX" VALUE="8467"> <PARAM NAME="_ExtentY" VALUE="6350"></OBJECT> </BODY> </HTML> </li> Click on both command buttons.</li></ol>

RESULT: The ambient back color of the Web page changes, but the AmbientChanged event never fires for the control.

Keywords: kbbug kbfix kbvs600fix kbinetdev kbctrl KB196219

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