Your ViewModelLocator
and Application
resides in different project. Hence there assemblies are different, so you need to provide assembly name along with namespace name in XAML definition.
xmlns:vm="clr-namespace:EasyDevis.EasyDevisPCL.ViewModel;assembly=AssemblyName"
Open properties of your PCL project and go to application tab, you will see AssemblyName
over there. Replace that assembly name with AssemblyName
in XAML.