Xamarin Forms : Triggers {Programmatically}

using System;
using ReXamForms.util;
using Xamarin.Forms;

namespace ReXamForms.ui
{
    public class TriggersPage : ContentPage
    {
        public TriggersPage()
        {
            initUi();
        }

        private void initUi()
        {
            Title = "Triggers";
            BackgroundColor = Color.FromHex(AppConstant.COLOR_PAGE_BACKGROUND);

            Label propertyLabel = new Label
            {
                HorizontalOptions = LayoutOptions.Start,
                Text = "Property Trigger - Background changes to DimGray on Focus.",
                TextColor = Color.White,
                FontAttributes = FontAttributes.Bold | FontAttributes.Italic,
                FontSize = Device.GetNamedSize(NamedSize.Large, typeof(Label))
            };

            Entry myEntry1 = new Entry
            {
                Placeholder = "Tap to focus...",
                PlaceholderColor = Color.White,
                BackgroundColor = Color.FromHex("#484848"),
                TextColor = Color.White,
                Margin = new Thickness(0, 0, 0, 20)
            };
            //PROPERTY TRIGGER
            Trigger propertyTrigger = new Trigger(typeof(Entry));
            propertyTrigger.Property = IsFocusedProperty;
            propertyTrigger.Value = true;

            Setter setter = new Setter();
            setter.Property = BackgroundColorProperty;
            setter.Value = Color.DimGray;

            propertyTrigger.Setters.Add(setter);
            myEntry1.Triggers.Add(propertyTrigger);//entry focus .. changes entry background color.
            //END PROPERTY TRIGGER

            Label dataLabel = new Label
            {
                HorizontalOptions = LayoutOptions.Start,
                Text = "Data Trigger - Button is disabled if entry is empty.",
                TextColor = Color.White,
                FontAttributes = FontAttributes.Bold | FontAttributes.Italic,
                FontSize = Device.GetNamedSize(NamedSize.Large, typeof(Label))
            };

            Entry myEntry2 = new Entry
            {
                Placeholder = "Enter something and delete...",
                PlaceholderColor = Color.White,
                BackgroundColor = Color.FromHex("#484848"),
                TextColor = Color.White,
                Margin = new Thickness(0, 0, 0, 10)
            };

            Button triggerButton = new Button
            {
                Text = "Data Trigger",
                TextColor = Color.White,
                FontAttributes = FontAttributes.Bold,
                FontSize = Device.GetNamedSize(NamedSize.Medium, typeof(Button)),
                BackgroundColor = Color.FromHex("#484848"),
                Margin = new Thickness(0, 0, 0, 20)
            };
            triggerButton.Clicked += (sender, e) => { Console.WriteLine("Data Trigger button clicked."); };

            //DATA TRIGGER
            DataTrigger dataTrigger = new DataTrigger(typeof(Button));
            Binding dataBinding = new Binding();
            dataBinding.Source = myEntry2;
            dataBinding.Path = "Text.Length";
            dataTrigger.Binding = dataBinding;
            dataTrigger.Value = 0;

            Setter dataSetter1 = new Setter();
            dataSetter1.Property = IsEnabledProperty;
            dataSetter1.Value = false;

            Setter dataSetter2 = new Setter();
            dataSetter2.Property = Button.TextProperty;
            dataSetter2.Value = "Data Trigger Enforced.";

            dataTrigger.Setters.Add(dataSetter1);
            dataTrigger.Setters.Add(dataSetter2);
            triggerButton.Triggers.Add(dataTrigger);//if entry text > 0 enabled else disabled.
            //END DATA TRIGGER

            Label eventLabel = new Label
            {
                HorizontalOptions = LayoutOptions.Start,
                Text = "Event Trigger - Text color changes on validation.",
                TextColor = Color.White,
                FontAttributes = FontAttributes.Bold | FontAttributes.Italic,
                FontSize = Device.GetNamedSize(NamedSize.Large, typeof(Label))
            };

            Entry myEntry3 = new Entry
            {
                Placeholder = "Green = OK, Red = Error.",
                PlaceholderColor = Color.White,
                BackgroundColor = Color.FromHex("#484848"),
                TextColor = Color.White,
                Margin = new Thickness(0, 0, 0, 20)
            };
            //EVENT TRIGGER
            EventTrigger entryEventTrigger = new EventTrigger();
            entryEventTrigger.Event = "TextChanged";
            entryEventTrigger.Actions.Add(new NumericValidationTriggerAction());
            myEntry3.Triggers.Add(entryEventTrigger);//entry TextChanged event .. checks entered valid double and changes entry color.
            //END EVENT TRIGGER

            Label multiLabel = new Label
            {
                HorizontalOptions = LayoutOptions.Start,
                Text = "Multi Trigger - Button enabled on validation.",
                TextColor = Color.White,
                FontAttributes = FontAttributes.Bold | FontAttributes.Italic,
                FontSize = Device.GetNamedSize(NamedSize.Large, typeof(Label))
            };

            Entry myEntry4 = new Entry
            {
                Placeholder = "Enter 2 characters...",
                PlaceholderColor = Color.White,
                BackgroundColor = Color.FromHex("#484848"),
                TextColor = Color.White,
                Margin = new Thickness(0, 0, 0, 10)
            };

            Entry myEntry5 = new Entry
            {
                Placeholder = "Enter 4 characters...",
                PlaceholderColor = Color.White,
                BackgroundColor = Color.FromHex("#484848"),
                TextColor = Color.White,
                Margin = new Thickness(0, 0, 0, 10)
            };

            Button multiTriggerButton = new Button
            {
                Text = "Multi Trigger",
                TextColor = Color.White,
                FontAttributes = FontAttributes.Bold,
                FontSize = Device.GetNamedSize(NamedSize.Medium, typeof(Button)),
                BackgroundColor = Color.FromHex("#484848"),
                Margin = new Thickness(0, 0, 0, 10),
                IsEnabled = false
            };
            multiTriggerButton.Clicked += (sender, e) => { Console.WriteLine("Multi Trigger button clicked."); };

            //MULTI TRIGGER
            MultiTrigger multiTrigger = new MultiTrigger(typeof(Button));
            BindingCondition bindingCondition1 = new BindingCondition()
            {
                Binding = new Binding("Text") { Path = "Text.Length", Source = myEntry4 },
                Value = "2"
            };

            BindingCondition bindingCondition2 = new BindingCondition()
            {
                Binding = new Binding("Text") { Path = "Text.Length", Source = myEntry5 },
                Value = "4"
            };

            multiTrigger.Conditions.Add(bindingCondition1);
            multiTrigger.Conditions.Add(bindingCondition2);

            Setter multiSetter1 = new Setter();
            multiSetter1.Property = IsEnabledProperty;
            multiSetter1.Value = true;

            Setter multiSetter2 = new Setter();
            multiSetter2.Property = BackgroundColorProperty;
            multiSetter2.Value = Color.Purple;

            multiTrigger.Setters.Add(multiSetter1);
            multiTrigger.Setters.Add(multiSetter2);
            multiTriggerButton.Triggers.Add(multiTrigger);//button is enabled if both entry are of length =2 and =4 respectively.
            //END MULTI TRIGGER




            FlexLayout mainContainerFlexLayout = new FlexLayout
            {
                Direction = FlexDirection.Column,
                Margin = new Thickness(25, 10, 25, 0),
                Children = { propertyLabel, myEntry1, dataLabel, myEntry2, triggerButton, eventLabel, myEntry3, multiLabel, myEntry4, myEntry5, multiTriggerButton }
            };

            Content = mainContainerFlexLayout;
        }
    }

    //Class for Event Triggers.
    public class NumericValidationTriggerAction : TriggerAction<Entry>
    {
        protected override void Invoke(Entry entry)
        {
            double result;
            bool isValid = Double.TryParse(entry.Text, out result);
            entry.TextColor = isValid ? Color.GreenYellow : Color.Red;
        }
    }
}