TL;DR: open the whole solution in blend*.
*for my scenario.
On using the Open In Blend menu option from right clicking a view in Visual Studio…
…I was experiencing the following System.NullReferenceException when opening the view in the Designer…
…on further investigation “The Resource “Locator” Could not be resolved.”
Explanation
When you right click Open in Blend, it will open the project that your view resides in, along with the View itself in the design window. What it won’t do however, is bring with it any resources it requires from other projects at design time. In this case, my App.xaml file located within the .Shared project, and NOT the platform specific project being loaded was defining my static resources and as such it could not be resolved due to not currently being loaded in Expression Blend. As mentioned in a previous post, the shared folder for all intents and purposes is part of the platform specific projects at compile time.
Resolution
My resolution was simple, open the entire Solution in Blend allowing it to be resolved!
Seems obvious now but I was stumped for a little while there! Hopefully this will come in handy to someone.
Mike Childs 