how to access current open file from custom ToolWindowPane

I have created ToolWindowPane (ToolBar for VS2008) using VSPackage but I am not able to access current opened file by the user. Is there any way to do this ? I wrote following code which travels through project and find out all element开发者_运维技巧s in opened solution.

EnvDTE.DTE dte = (EnvDTE.DTE)Microsoft.VisualStudio.Shell.Package.GetGlobalService(typeof(EnvDTE.DTE));

But not able to get reference of open file by user I also want each time user change focus from one file to another my toolbar should refresh.

Thanks in advance

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You could try using the events model?

http://msdn.microsoft.com/en-us/library/envdte.events.aspx