How do you cancel a ToolWindowPane or Visual Studio IDE close operation via a VSPackage?

I have a VSPackage with a dockable tool window containing form data. If there are unsaved changes in this form, I would like to cancel a close to either the tool window and the visual studio IDE if the user clicks cancel on saving changes before closing. I can perform the save test on close, but I don't see any event handler methods or other options to actually cancel the close.

Here is some blurb from the package:

    private DTE2 _applicationObject = null;
    ///--------------------------------------------------------------------------------
    /// <summary>This property gets the visual studio IDE application object.</summary>
    ///--------------------------------------------------------------------------------
    public DTE2 ApplicationObject
    {
        get
        {
            if (_applicationObject == null)
            {
                // Get an instance of the currently running Visual Studio IDE
                DTE dte = (DTE)GetService(typeof(DTE));
                _applicationObject = dte as DTE2;
            }
            return _applicationObject;
        }
    }
    ///--------------------------------------------------------------------------------
    /// <summary>
    /// Initialization of the package; this method is called right after the package is sited, so this is the place
    /// where you can put all the initilaization code that rely on services provided by VisualStudio.
    /// </summary>
    ///--------------------------------------------------------------------------------
    protected override void Initialize()
    {
        Trace.WriteLine(string.Format(CultureInfo.CurrentCulture, "Entering Initialize() of: {0}", this.ToString()));
        base.Initialize();

        // add the event handlers
        if (ApplicationObject != null)
        {
            // wire up window events
            PackageWindowEvents = (WindowEvents)ApplicationObject.Events.get_W开发者_如何学CindowEvents(null);
            PackageWindowEvents.WindowClosing += new _dispWindowEvents_WindowClosingEventHandler(PackageWindowEvents_WindowClosing);

            // wire up solution events
            PackageSolutionEvents = ApplicationObject.Events.SolutionEvents;
            PackageSolutionEvents.Opened += new _dispSolutionEvents_OpenedEventHandler(CheckOpenCurrentSolution);

            // wire up DTE events
            PackageDTEEvents = ApplicationObject.Events.DTEEvents;
            PackageDTEEvents.OnBeginShutdown += new _dispDTEEvents_OnBeginShutdownEventHandler(HandleVisualStudioShutdown);
        }
    }

    void PackageWindowEvents_WindowClosing(Window window)
    {
        // handle save/cancel scenarios
    }

And some blurb from the ToolWindowPane that implements IVsWindowFrameNotify3:

    protected override void OnClose()
    {
        base.OnClose();
    }
    public int OnClose(ref uint pgrfSaveOptions)
    {
        return (int)__FRAMECLOSE.FRAMECLOSE_PromptSave;
    }

The OnClose and WindowClosing methods fire when expected, but I'm not finding a way to cancel the close. What am I missing? Are there different events required to cancel a close?

For completeness, there IS a useful way to cancel a close with a tool window (provided by user Chicobo on the msdn forum and repeated here).

1. In your ToolWindowPane class, implement the IVsWindowFrameNotify2 interface, which provides a method OnClose.

2. To cancel the window closing, consider using :

   public int OnClose(ref uint pgrfSaveOptions)
   {
       // Check if your content is dirty here, then
   
       // Prompt a dialog
       MessageBoxResult res = MessageBox.Show("This Document has been modified. Do you want to save the changes ?",
                     "Unsaved changes", MessageBoxButton.YesNoCancel, MessageBoxImage.Warning);
       // If the users wants to save
       if (res == MessageBoxResult.Yes)
       {
           // Handle with your "save method here"
       }
   
       if (res == MessageBoxResult.Cancel)
       {
           // If "cancel" is clicked, abort the close
           return VSConstants.E_ABORT;
       }
   
       // Else, exit
       return VSConstants.S_OK;
   }
   

For the purpose of completing the previous answer, the following code snippet targets an unanswered part of the question which is on how to prevent the close operation of the Visual Studio IDE inside a VsPackage:

    protected override int QueryClose(out bool pfCanClose)
    {
        pfCanClose = false;
        return VSConstants.S_OK;
    }

Use the above code inside your package class.