If you are building a XAML based WinRT application which uses a GridView it is very likely you are going to use an ItemTemplate style OR use the ItemTemplateSelector to determine which style to use.  This is great and using either of these could not be any easier.  HOWEVER, make sure you do not have both of them set at the same time in your XAML.  Because if you do use them both you will be left to wonder why your TemplateSelector code is NOT working, but your provided style is.

As far as I can tell the ItemTemplate trumps the ItemTemplateSelector and your selector will NEVER get executed.

You will want to either use just the ItemTemplate OR use the ItemTemplateSelector.

Hope this helps.

Till next time,