This line turn off the default options into Xamarin form to make all button text Upper Case.
<item name="android:textAllCaps">false</item>
This line of code enable CollectionView usage into Xamarin Forms application since the feature it is not 100% released.
Forms.SetFlags("CollectionView_Experimental");
First of all you need to bring the design namespace on your xaml.
xmlns:d="http://xamarin.com/schemas/2014/forms/design"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
Then your can set the proper ViewModel for you page
<d:ContentPage.BindingContext>
<viewmodels:CustomViewModel />
</d:ContentPage.BindingContext>
Now enjoy the Intellisense!
I am about to report it asap. Thank you for your time!