To monitor the state of Explorer windows, you can handle the following Explorer-related events:

• NewExplorer

• Activate

• Close

• Deactivate

To monitor the state of Inspector windows, you can handle the following Inspector-related events:

• NewInspector

• Activate

• Close

• Deactivate

To prevent Outlook windows from displaying multiple instances of a custom task pane, explicitly remove the custom task pane from the CustomTaskPanes collection of the ThisAddIn class when each window is closed. Call the Remove method in an event that is raised when a window is closed, such as ExplorerEvents_10_Event..::.Close or InspectorEvents_10_Event..::.Close.

If you do not explicitly remove the custom task pane, Outlook windows might display multiple instances of the custom task pane. Outlook sometimes recycles windows, and recycled windows retain references to any custom task panes that were attached to them.

To monitor the state of document windows in Word, you can handle the following events:

• DocumentBeforeClose

• DocumentOpen

• NewDocument

• WindowActivate

• WindowDeactivate

To monitor the state of document windows in InfoPath, you can handle the following events:

• NewXDocument

• WindowActivate

• WindowDeactivate

• XDocumentBeforeClose

• XDocumentOpen

To monitor the state of workbooks in Excel, you can handle the following events:

• NewWorkbook

• WindowActivate

• WindowDeactivate

• WorkbookActivate

• WorkbookDeactivate

• WorkbookOpen

To monitor the state of presentations in PowerPoint, you can handle the following events:

• Microsoft.Office.Interop.PowerPoint.EApplication_Event.AfterNewPresentation

• Microsoft.Office.Interop.PowerPoint.EApplication_Event.AfterPresentationOpen

• Microsoft.Office.Interop.PowerPoint.EApplication_Event.NewPresentation

• Microsoft.Office.Interop.PowerPoint.EApplication_Event.PresentationOpen

• Microsoft.Office.Interop.PowerPoint.EApplication_Event.WindowActivate

• Microsoft.Office.Interop.PowerPoint.EApplication_Event.WindowDeactivate

The following code example demonstrates how to hide or display a custom task pane in an event handler for the WorkbookActivate event in an Excel add-in. When each workbook is activated, the task pane is visible only if the workbook is named SalesData.xls; otherwise, the task pane is hidden. To run this example, replace the default ThisAddIn_Startup event handler that Visual Studio Tools for Office generates in the ThisAddIn class with the following code. This example assumes that your project includes a UserControl named UserControl1.

Dim myUserControl As UserControl1
Dim myCustomTaskPane As Microsoft.Office.Tools.CustomTaskPane

Private Sub ThisAddIn_Startup(ByVal sender As Object, ByVal e As System.EventArgs) _
Handles Me.Startup
    myUserControl = New UserControl1()
    myCustomTaskPane = Me.CustomTaskPanes.Add(myUserControl, "Sales Task Pane")
End Sub

Private Sub Application_WorkbookActivate(ByVal Wb As Excel.Workbook) _
    Handles Application.WorkbookActivate

    If Wb.Name = "SalesData.xlsx" Then
        myCustomTaskPane.Visible = True
    Else
        myCustomTaskPane.Visible = False
    End If
End Sub

private UserControl1 myUserControl;
private Microsoft.Office.Tools.CustomTaskPane myCustomTaskPane;

private void ThisAddIn_Startup(object sender, System.EventArgs e)
{
    this.Application.WorkbookActivate += new Excel.AppEvents_WorkbookActivateEventHandler(
        Application_WorkbookActivate);

    myUserControl = new UserControl1();
    myCustomTaskPane = this.CustomTaskPanes.Add(myUserControl, "Sales Task Pane");
}

void Application_WorkbookActivate(Excel.Workbook Wb)
{
    if (Wb.Name == "SalesData.xlsx")
        myCustomTaskPane.Visible = true;
    else
        myCustomTaskPane.Visible = false;
}