Supply an identifier name for this view, to later retrieve it with Android.Views.View.FindViewById(int) or Android.App.Activity.FindViewById(int). This must be a resource reference; typically you set this using the @+ syntax to create a new ID resources. For example: android:id="@+id/my_id" which allows you to later retrieve the view with findViewById(R.id.my_id).

Must be a reference to another resource, in the form "@[+][package:]type:name" or to a theme attribute in the form "?[package:][type:]name".

[Android Documentation]