UIPickerView BordersPickerView; //the view for the picker

        public GeneralMaintenanceScreen()
        {
            //create screen
            Screen = new UIViewController();
            Screen.View.BackgroundColor = UIColor.White;

            //1. create view
            //pages label
            PagesLabel               = new UILabel();
            PagesLabel.Text          = "Number of pages:";
            PagesLabel.TextColor     = UIColor.Black;
            PagesLabel.TextAlignment = UITextAlignment.Left;

            //buttons label
            ButtonsLabel               = new UILabel();
            ButtonsLabel.Text          = "Number of buttons:";
            ButtonsLabel.TextColor     = UIColor.Black;
            ButtonsLabel.TextAlignment = UITextAlignment.Left;

            //borders label
            BordersLabel               = new UILabel();
            BordersLabel.Text          = "Borders thickness:";
            BordersLabel.TextColor     = UIColor.Black;
            BordersLabel.TextAlignment = UITextAlignment.Left;

            //buttons per page dropdown
            ButtonsPickerModel = new PickerModel(ButtonsNum);
            ButtonsPickerModel.PickerChanged += (object sender, PickerChangedEventArgs e) =>
            {
                Debug.WriteLine("picker changed");
                Debug.WriteLine("value selected" + e.SelectedValue);
                ButtonsPerPage = Int32.Parse(e.SelectedValue.ToString());
            };
            //add picker model to ui picker and some styling
            ButtonsPickerView       = new UIPickerView();
            ButtonsPickerView.Model = ButtonsPickerModel;
            ButtonsPickerView.ShowSelectionIndicator = true;
            ButtonsPickerView.BackgroundColor        = UIColor.White;
            ButtonsPickerView.Layer.BorderColor      = UIColor.Gray.CGColor;
            ButtonsPickerView.Layer.BorderWidth      = 4.5f;
            ButtonsPickerView.Layer.CornerRadius     = ButtonCornerRadius;

            //pages dropdown
            //create picker model, and add function event when it changes
            //function will change the text fields value
            PagesPickerModel = new PickerModel(PagesNum);
            PagesPickerModel.PickerChanged += (object sender, PickerChangedEventArgs e) =>
            {
                Debug.WriteLine("picker changed");
                Debug.WriteLine("value selected" + e.SelectedValue);
                NumberOfPages = Int32.Parse(e.SelectedValue.ToString());
            };
            //add picker model to ui picker and some styling
            PagesPickerView       = new UIPickerView();
            PagesPickerView.Model = PagesPickerModel;
            PagesPickerView.ShowSelectionIndicator = true;
            //PagesPickerView.Frame = new CoreGraphics.CGRect(250, 150, 60, 60);
            PagesPickerView.BackgroundColor    = UIColor.White;
            PagesPickerView.Layer.BorderColor  = UIColor.Gray.CGColor;
            PagesPickerView.Layer.BorderWidth  = 4.5f;
            PagesPickerView.Layer.CornerRadius = ButtonCornerRadius;

            //borders dropdown
            //create picker model, and add function event when it changes
            //function will change the text fields value
            BordersPickerModel = new PickerModel(BordersNum);
            BordersPickerModel.PickerChanged += (object sender, PickerChangedEventArgs e) =>
            {
                Debug.WriteLine("picker changed");
                Debug.WriteLine("value selected" + e.SelectedValue);
                BordersThickness = Int32.Parse(e.SelectedValue.ToString());
            };
            //add picker model to ui picker and some styling
            BordersPickerView       = new UIPickerView();
            BordersPickerView.Model = BordersPickerModel;
            BordersPickerView.ShowSelectionIndicator = true;
            BordersPickerView.BackgroundColor        = UIColor.White;
            BordersPickerView.Layer.BorderColor      = UIColor.Gray.CGColor;
            BordersPickerView.Layer.BorderWidth      = 4.5f;
            BordersPickerView.Layer.CornerRadius     = ButtonCornerRadius;

            //create back button
            BackButton = new UIButton();
            BackButton.BackgroundColor = UIColor.Red;
            BackButton.TouchUpInside  += CloseScreen;
            BackButton.SetTitle("Back", UIControlState.Normal);
            BackButton.SetTitleColor(UIColor.Black, UIControlState.Normal);
            BackButton.Layer.BorderColor  = ButtonBorderColour.CGColor;
            BackButton.Layer.BorderWidth  = BordersThickness;
            BackButton.BackgroundColor    = ButtonBackgroundColour;
            BackButton.Layer.CornerRadius = ButtonCornerRadius;

            //create save button
            SaveButton = new UIButton();
            SaveButton.BackgroundColor = UIColor.Red;
            SaveButton.TouchUpInside  += Save;
            SaveButton.SetTitle("Save", UIControlState.Normal);
            SaveButton.SetTitleColor(UIColor.Black, UIControlState.Normal);
            SaveButton.Layer.BorderColor  = ButtonBorderColour.CGColor;
            SaveButton.Layer.BorderWidth  = BordersThickness;
            SaveButton.BackgroundColor    = ButtonBackgroundColour;
            SaveButton.Layer.CornerRadius = ButtonCornerRadius;

            //2. add view to parent view
            Screen.View.Add(PagesLabel);
            Screen.View.Add(ButtonsLabel);
            Screen.View.Add(ButtonsPickerView);
            Screen.View.Add(PagesPickerView);
            Screen.View.Add(BackButton);
            Screen.View.Add(SaveButton);
            Screen.View.Add(BordersLabel);
            Screen.View.Add(BordersPickerView);

            //3. call method on parent view
            Screen.View.SubviewsDoNotTranslateAutoresizingMaskIntoConstraints();

            //4. add constraints
            Screen.View.AddConstraints(
                PagesLabel.WithSameTop(BackButton),
                PagesLabel.AtLeftOf(Screen.View, 70),
                PagesLabel.WithRelativeWidth(Screen.View, 0.2f),
                //PagesLabel.Width().EqualTo(150),
                PagesLabel.Height().EqualTo(45),

                ButtonsLabel.WithSameTop(SaveButton),
                ButtonsLabel.WithSameLeft(PagesLabel),
                ButtonsLabel.WithSameWidth(PagesLabel),
                ButtonsLabel.WithSameHeight(PagesLabel),

                BordersLabel.Below(SaveButton, 80),//
                BordersLabel.WithSameLeft(PagesLabel),
                BordersLabel.WithSameWidth(PagesLabel),
                BordersLabel.WithSameHeight(PagesLabel),

                ButtonsPickerView.WithSameTop(ButtonsLabel),
                ButtonsPickerView.Left().EqualTo().RightOf(ButtonsLabel).Plus(30),
                ButtonsPickerView.Width().EqualTo(60),
                ButtonsPickerView.Height().EqualTo(60),

                PagesPickerView.WithSameTop(PagesLabel),
                PagesPickerView.WithSameLeft(ButtonsPickerView),
                PagesPickerView.WithSameWidth(ButtonsPickerView),
                PagesPickerView.WithSameHeight(ButtonsPickerView),

                BordersPickerView.WithSameTop(BordersLabel),//
                BordersPickerView.WithSameLeft(ButtonsPickerView),
                BordersPickerView.WithSameWidth(ButtonsPickerView),
                BordersPickerView.WithSameHeight(ButtonsPickerView),

                BackButton.AtTopOf(Screen.View, UIApplication.SharedApplication.StatusBarFrame.Height + 70),
                BackButton.AtRightOf(Screen.View, 70),
                BackButton.WithRelativeWidth(Screen.View, 0.2f),
                BackButton.Height().EqualTo(100),

                SaveButton.Below(BackButton, 80),
                SaveButton.WithSameRight(BackButton),
                SaveButton.WithSameWidth(BackButton),
                SaveButton.WithSameHeight(BackButton)
                );
        }