Knowledge Base

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

Article ID: 196219

Article Last Modified on 10/16/2002


APPLIES TO


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.

MORE INFORMATION

Steps to reproduce behavior

  1. Create a new user control project in Visual Basic.
  2. Add two command buttons to the default form for the control.
  3. 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
    					
  4. Make the control.
  5. Place the control on a Web page (make sure you replace the CLSID in the code below):
    <HTML>
    <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>
    					
  6. Click on both command buttons.
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