-2
Listview is a component for displaying the data list on the screen. To do this you must define a data source to popular Listview as a list(List), vector(Array) or any Ienumerable.
In your case you are not passing any data source to your Listview submit.
Listview documentation: https://docs.microsoft.com/pt-br/xamarin/xamarin-forms/user-interface/listview/