Get Size in iOS Project

Hi,
Render.Model.Width or Height always returning -1, How can I get Width or Height in Native project:

`

    public class MyNavigationRenderer : Xamarin.Forms.Platform.iOS.NavigationRenderer {

    public void ShowDialog(Xamarin.Forms.View view) {
        using (var renderer = Xamarin.Forms.Platform.iOS.RendererFactory.GetRenderer(view)) {

            var popup = renderer.NativeView;
            UIButton background = new UIButton();
            this.View.Window.RootViewController.View.AddSubview(background);
            this.View.Window.RootViewController.View.AddSubview(popup);

            background.BackgroundColor = UIColor.Black;
            popup.SizeToFit();
            background.SizeToFit();

            background.TitleLabel.Text = "";


            popup.Alpha = 0;
            popup.Frame = new RectangleF(new PointF(100, 100), new SizeF(1, 1));
            background.Alpha = 0.6f;
            background.Frame = background.Window.Frame;

            UIButton.Animate(0.4, () => {
                popup.Alpha = 1;

        //*****************************************************
        // renderer.Model.Width returning -1
                popup.Frame = new System.Drawing.RectangleF(0, 0, Convert.ToSingle(renderer.Model.Width), Convert.ToSingle(renderer.Model.Height));

                popup.Center = background.Window.Center;
            });


            background.TouchUpInside += (object sender, EventArgs e) => {
                UIButton.Animate(.3, () => {
                    popup.Alpha = 0;
                    popup.Frame = new RectangleF(new PointF(100, 100), new SizeF(1, 1));
                    background.Alpha = 0;
                }, () => {
                    background.RemoveFromSuperview();
                    popup.RemoveFromSuperview();
                });
            };
        }
    }

`

And this is my code in PCL Project:

`

            var p2 = new StackLayout {
                BackgroundColor = Color.Red, WidthRequest = 200, HeightRequest = 200,
                Children = { new Button(){ Text = "Hello" }
                 }
            };

            Parent.ShowDialog(p2);

`

Thanks.