My WPF app has a MainWindow containing a usercontrol called TvshowGridView.
MainWindow:
Assuming that your MainWindows Datacontext is an instance of MainWindowViewModel, you can bind the usercontrol to TvshowGridViewModel like this:
...
You also should change the TvshowGridViewModel property code like shown:
public TvshowGridViewModel TvshowGridViewModel
{ get{return _tvshowGridViewModel;} }