Outlook VSTO CustomPanesIssue.Add - Such Interface is not supported

Question

I am working on Outlook VSTO Plugins to display a message on top of Current Opened Window. Such as I want to display a message to user when try to "Reply All" on certain conditions. On Email it is working fine but same is not working on Meeting.

Case Email - (Reply, Reply All, New)

It is working fine code as is follows.

     'Starup Event to initialize control objects
            Private Sub ThisAddIn_Startup() Handles Me.Startup
                Try
                    'Insitialize outlook inspector.
                    inspectors = Globals.ThisAddIn.Application.Inspectors
        
                    'Create new inspector
                    AddHandler inspectors.NewInspector, AddressOf inspectors_NewInspector
       
        
                Catch ex As System.Exception
                    'MessageBox.Show(ex.StackTrace)
                End Try
        
            End Sub
    
      
    
    Sub inspectors_NewInspector(inspector As Microsoft.Office.Interop.Outlook.Inspector)
        Try
            subInspector = inspector
    
            Dim mailItem As Outlook.MailItem
            mailItem = DirectCast(inspector.CurrentItem, Outlook.MailItem)
    
            'AddHandler mailItem.Open, AddressOf explorer_onOpen
    
        Catch ex As System.Exception
    
        End Try
    End Sub

      Private Sub explorer_onOpen()
        'I am using Thread to wait few seconds until New Email Windows open.
        'Else message message bar display on the windows which opened and on top. and 
         ' New/Reply email windows takes some time to appear.
        
        Dim thread As New Thread(AddressOf MyBackgroundThread)
        thread.IsBackground = True
        thread.Start()
    End Sub

 Private Sub MyBackgroundThread()
        Try
            'Pause code for 2.5 seconds
            Thread.Sleep(2500)
            MessageBox.Show("Threading")

            _obj = New UserControl2
            Dim _pane1 = Globals.ThisAddIn.CustomTaskPanes.Add(_obj,"Test",Globals.ThisAddIn.Application.ActiveWindow)
           _pane1.Visible=True
        Catch ex As System.Exception
            MessageBox.Show(ex.Message)
        End Try

    End Sub

But the same code is not working on AppointmentItem. Code is as follows. Only changes I have done in Open event and Thread

Sub inspectors_NewInspector(inspector As Microsoft.Office.Interop.Outlook.Inspector)
        Try
            subInspector = inspector            
            Dim appouitmentItem As Outlook.AppointmentItem
            appouitmentItem = DirectCast(inspector.CurrentItem, Outlook.AppointmentItem)

            AddHandler appouitmentItem.Open, AddressOf explorer_onOpen

        Catch ex As System.Exception

        End Try
    End Sub

    Private Sub explorer_onOpen()
        'Thread to display warning message after few seconds
        MessageBox.Show("Thread to display warning message after few seconds")
        Dim thread As New Thread(AddressOf MyBackgroundThread)
        thread.IsBackground = True
        thread.Start()

    End Sub

 Private Sub MyBackgroundThread()
        Try
            'Pause code for 2.5 seconds
            Thread.Sleep(2500)
            MessageBox.Show("Threading")

            _obj = New UserControl2
                Dim _pane1 = Globals.ThisAddIn.CustomTaskPanes.Add(_obj,"Test",Globals.ThisAddIn.Application.ActiveWindow)
               _pane1.Visible=True
        Catch ex As System.Exception
            MessageBox.Show(ex.Message)
        End Try

    End Sub

I am getting error Unable to cast COM object type 'System._ComObject' to interface type 'Microsoft.VisualStudio.Tools.Office.Runtime.ICustomTaskPaneSite'. This operation faled because the QueryInterface call on teh COM component for the itnterface with IID{} failed due to the following error: No Such interface supported.

Environment: Visual Studio 2019 Office 2016

Eugene Astafiev Eugene Astafiev · Accepted Answer · 2021-06-10T06:25:41

First of all, there is no need to use task panes for inspector windows in Outlook. Instead, you may consider using Outlook form regions. Form regions offer many enhancements over traditional Outlook forms development:

Customize the default page of any standard form.
Add up to 12 extra pages to any standard form.
Replace or enhance any standard form.
Display custom UI in the Reading Pane and in Inspectors.

For more information, see Customize form pages and form regions.

The FormRegionInitializing event handler is exposed in the form region code file. You can use this event handler to specify whether Outlook should display the form region. For more information, see Handle form region events.

Also you need to run the code from the main thread (UI thread) because Outlook uses a single-threaded apartment model. Moreover, any UI changes should be made from the main thread.

Outlook VSTO CustomPanesIssue.Add - Such Interface is not supported

Case Email - (Reply, Reply All, New)

1 Answers