A Xamarin.Forms Effect where you can subscribe to an event handler when the keyboard is shown

ConversionHelpers.cs

public static class ConversionHelpers
    {
        public static Xamarin.Forms.Rectangle AsRectangle(this CGRect o)
        {
            return new Xamarin.Forms.Rectangle
            {
                Height = o.Height,
                Width = o.Width,
                X = o.X,
                Y = o.Y,
                Bottom = o.Bottom,
                Top = o.Top,
                Left = o.Left,
                Location = o.Location.ToPoint()
            };
        }
    }

CustomKeyboardEventArgs.cs

public class CustomKeyboardEventArgs : EventArgs
    {
        public CustomKeyboardEventArgs(Rectangle frameStart, Rectangle frameEnd)
        {
            this.FrameStart = frameStart;
            this.FrameEnd = frameEnd;
        }

        public Rectangle FrameStart { get; }

        public Rectangle FrameEnd { get; }
    }

KeyboardNotificationEffect.cs

public class KeyboardNotificationEffect : RoutingEffect
    {
        public event EventHandler<CustomKeyboardEventArgs> KeyboardShown;
        public event EventHandler<CustomKeyboardEventArgs> KeyboardHidden;
        
        public KeyboardNotificationEffect()
            : base("Telerik.KeyboardNotificationEffect")
        { }

        public void InvokeShown(Rectangle frameStart, Rectangle frameEnd)
        {
            KeyboardShown?.Invoke(this, new CustomKeyboardEventArgs(frameStart, frameEnd));
        }

        public void InvokeHidden(Rectangle frameStart, Rectangle frameEnd)
        {
            KeyboardHidden?.Invoke(this, new CustomKeyboardEventArgs(frameStart, frameEnd));
        }
    }

KeyboardNotificationEffect.iOS.cs

[assembly: ResolutionGroupName("Telerik")]
[assembly: ExportEffect(typeof(YourProject.iOS.Effects.KeyboardNotificationEffect), "KeyboardNotificationEffect")]
namespace YourProject.iOS.Effects
{
    public class KeyboardNotificationEffect : PlatformEffect
    {
        protected override void OnAttached()
        {
            UIKeyboard.Notifications.ObserveWillShow(UIKeyboard_WillShow);
            UIKeyboard.Notifications.ObserveWillHide(UIKeyboard_WillHide);
        }

        protected override void OnDetached()
        {
        }

        private void UIKeyboard_WillHide(object sender, UIKeyboardEventArgs e)
        {
            if (Element.Effects.FirstOrDefault(ef => ef is ArtGalleryCRM.Forms.Effects.KeyboardNotificationEffect) is ArtGalleryCRM.Forms.Effects.KeyboardNotificationEffect effect)
            {
                effect.InvokeHidden(e.FrameBegin.AsRectangle(), e.FrameEnd.AsRectangle());
            }
        }

        private void UIKeyboard_WillShow(object sender, UIKeyboardEventArgs e)
        {
            if (Element.Effects.FirstOrDefault(ef => ef is ArtGalleryCRM.Forms.Effects.KeyboardNotificationEffect) is ArtGalleryCRM.Forms.Effects.KeyboardNotificationEffect effect)
            {
                effect.InvokeShown(e.FrameBegin.AsRectangle(), e.FrameEnd.AsRectangle());
            }
        }
    }
}

MainPage.xaml

<conversationalUi:RadChat ...>
    <conversationalUi:RadChat.Effects>
        <effects:KeyboardNotificationEffect KeyboardShown="KeyboardNotificationEffect_OnKeyboardShown" KeyboardHidden="KeyboardNotificationEffect_OnKeyboardHidden"/>
    </conversationalUi:RadChat.Effects>
</conversationalUi:RadChat>

MainPage.xaml.cs

private void KeyboardNotificationEffect_OnKeyboardShown(object sender, CustomKeyboardEventArgs e)
{
    if (vm.Items.Count > 0)
    {
        var emptyMessage = vm.Items[0];

        if (emptyMessage.Category == MessageCategory.Empty)
        {
            emptyMessage.EmptyHeight = (double)e.FrameEnd.Height;
        }
    }
}

private void KeyboardNotificationEffect_OnKeyboardHidden(object sender, CustomKeyboardEventArgs e)
{
    if (vm.Items.Count > 0)
    {
        var emptyMessage = vm.Items[0];
	    
        if (emptyMessage.Category == MessageCategory.Empty)
        {
            emptyMessage.EmptyHeight = 0;
        }
    }
}