VSIP 2005: Tracking the Active Visual Studio Window

In a VSPackage using the Managed Package Framework (MPF), how do you track the active editor pane in VS? To start with, I create a new VSPackage project (New project -> Other project types -> Extensibility -> Visual Studio Integration Package) and have the wizard create a C# based project with a tool window for me. From the standard button click (to keep things under control easily), I run the following initialization code:

DTE dte = (DTE) GetService(typeof(DTE));

Window outputWindow = (Window) dte.Windows.Item(EnvDTE.Constants.vsWindowKindOutput);
outputWindow.Visible = true;
outputPane = ((OutputWindow) outputWindow.Object).OutputWindowPanes.Add("Active window tracking");
outputPane.Activate( );

IVsMonitorSelection monitorSelection = (IVsMonitorSelection) GetService(typeof(SVsShellMonitorSelection));
monitorSelection.AdviseSelectionEvents(this, out myCookie);

Two different things are being done here:

  1. An output pane is installed into the VS output window, titled Active window tracking, that I can use throughout my package to output debug information. The output pane is stored in a field of type OutputWindowPane, to be used later.
  2. The last two lines query the IVsMonitorSelection service from the VS shell, and install my class as an event receiver for event pertaining to selections. A selection in VS can be for any type of object that the IDE deals with, so windows are one such type. The cookie that’s returned by the call to AdviseSelectionEvents isn’t important for us, it’s stored away in a field of uint type.

Now the class has to implement the interface IVsSelectionEvents to be able to receive notifications about selections. The three methods of the interface are implemented here:

int IVsSelectionEvents.OnElementValueChanged(uint elementid, object varValueOld, object varValueNew) {
  if (elementid == (uint) VSConstants.VSSELELEMID.SEID_WindowFrame) {
    string oldCaption = GetWindowFrameCaption((IVsWindowFrame) varValueOld);
    string newCaption = GetWindowFrameCaption((IVsWindowFrame) varValueNew);
    LogWindowChange(oldCaption, newCaption);
  }
  return VSConstants.S_OK;
}

int IVsSelectionEvents.OnSelectionChanged(IVsHierarchy pHierOld, uint itemidOld, IVsMultiItemSelect
  pMISOld, ISelectionContainer pSCOld, IVsHierarchy pHierNew, uint itemidNew, IVsMultiItemSelect
  pMISNew, ISelectionContainer pSCNew) {
  return VSConstants.S_OK;
}

int IVsSelectionEvents.OnCmdUIContextChanged(uint dwCmdUICookie, int fActive) {
  return VSConstants.S_OK;
}

As you can see, the only method of interest to me is the OnElementValueChanged method, in which I evaluate the elementid to make sure that the given element is indeed a WindowFrame and I extract the window caption for demonstration purposes, which is then shown in the output window I installed in the beginning. Here are the missing helper functions:

void Log(string text ) {
  if (outputPane != null)
    outputPane.OutputString(text + Environment.NewLine);
}

void LogWindowChange(string oldCaption, string newCaption) {
  Log("Focus changed from '" + oldCaption + "' to '" + newCaption + "'");
}

string GetWindowFrameCaption(IVsWindowFrame frame) {
  object result = null;
  if (frame != null)
    frame.GetProperty((int) __VSFPROPID.VSFPROPID_Caption, out result);
  return (string) result;
}

Have fun!

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