DraggableView.v1.cs

    public class DraggableView : ContentView, IDisposable
    {
        public DraggableArea LimitArea { get; set; }

        protected override void OnParentSet()
        {
            base.OnParentSet();
            if (Parent is View parent)
            {
                parent.SizeChanged += Parent_SizeChanged;
            }
        }

        private void Parent_SizeChanged(object sender, EventArgs e)
        {
            if (sender is View {Height: > 0, Width: > 0} parent)
            {
                LimitArea = new DraggableArea(parent.X, parent.Y,
                        parent.Width,
                        parent.Height);
            }
        }

        public void Dispose()
        {
            if (Parent is View parent)
            {
                parent.SizeChanged -= Parent_SizeChanged;
            }
        }
    }