VSIP: ITrackSelection

Yesterday I was trying to access to the service STrackSelection (in order to change the selection in visual studio), I was very confused because in some cases the GetService failed.

For example when I requested the service in the package initialize the getservice failed.

protected class MyPackage : Package

 override void Initialize()

{           base.Initialize();

            ITrackSelection track = (ITrackSelection) GetService(typeof(STrackSelection));

}

However  If I implement a tool window and call the GetService on the service provider of the toolwindow the GetService call succeed

This behavior was very well explained by  Douglas Hodges (Microsoft):

“...ITrackSelection or IVsTrackSelectionEx (“SID_STrackSelection” or “SID_SVsTrackSelectionEx” respectively) are only available from the IServiceProvider that is implemented on the site object of a WindowFrame. Basically selection is tracked on a per-window basis. The site pointer that is used to site the IVsWindowPane object provides these TrackSelection services. You can not get these services from the global IServiceProvider that is passed to your IVsPackage object. So the easiest thing is when you are the IVsWindowPane object sited in an IVsWindowFrame, then you are passed the IServiceProvider to use as part of IVsWindowPane::SetSite. If you are not this object, you can still get to the IServiceProvider of an IVsWindowFrame by calling IVsWindowFrame::GetProperty(VSFPROPID_SPFrame, …). Remember you can only set the selection on a window; there is no notion of a global selection context. Each WindowFrame remembers its selection. When the window is activated, its selection is pushed to the global IVsMonitorSelection service that is used by anyone to get events when the selection changes.”