I can not assign a class in the Droid Project that is in the Shared Project

When I create a class in the APP and try to use it in the Droid, it is not recognized in the Droid, even adding the reference to it by the using clause. I create this class:

public partial class CircleView : BoxView
{
    public static readonly BindableProperty CornerRadiusProperty = BindableProperty.Create(nameof(CornerRadius), typeof(double), typeof(CircleView), 0.0);

    public double CornerRadius
    {
        get { return (double)GetValue(CornerRadiusProperty); }
        set { SetValue(CornerRadiusProperty, value); }
    }

    public CircleView()
    {
        InitializeComponent();
    }
}

And when I refer to it here, for example

[assembly: ExportRenderer(typeof(CircleView), typeof(RoundedBoxRenderer))]

error:

  

The name of the type or "CircleView" namespace can not be found ...

How do I resolve this?