Read original post at Rohit Sharma's Blog
Working with the default Win8 Gridview app (generated via VS 2012 GridView Template), I found it now supports a new way to share and access multiple view-models for a given view.
The idea is to bind the view’s DataContext property to a dictionary object (where key is the name of the viewmodel, and value is the viewmodel itself), you can then refer the viewmodel from XAML/View via Binding markup such as {Binding KeyName}. In other words, the Binding markup now supports KeyNames on the IObservableMap (beside getter properties).