Daniel Hindrikes

I often see code that for example binds colors and texts for a button when they want to show different color and/or text when app is in different states. For example a button for login/logout the XAML could look like below.

public class LoginButtonBehavior : Behavior
    {
        public static readonly BindableProperty IsLoggedInProperty =
        BindableProperty.Create("IsLoggedIn", typeof(bool), typeof(LoginButtonBehavior),
            null, propertyChanged: (bindable, oldValue, newValue) => {
                var behavior = (LoginButtonBehavior)bindable;
                behavior.Update();
            });

        public bool IsLoggedIn
        {
            get
            {
                return (bool)GetValue(IsLoggedInProperty);
            }
            set
            {
                SetValue(IsLoggedInProperty, value);
            }
        }


        public Button Control { get; set; }

        protected override void OnAttachedTo(Button bindable)
        {
            base.OnAttachedTo(bindable);

            Control = bindable;

           bindable.BindingContextChanged += (sender, _) => this.BindingContext = ((BindableObject)sender).BindingContext;
        }

        public void Update()
        {
            Device.BeginInvokeOnMainThread(() =>
            {
                 if(IsLoggedIn)
                 {
                       Control.BackgroundColor = Color.Red;
                       Control.Text = "Logout";
                 }
                 else
                 {
                       Control.BackgroundColor = Color.Green;
                       Control.Text = "Login";
                 }
            });
        }
    }

When we have created the behavior we will attach it to the button.

You can read more about behaviors at Xamarin's developer portal, https://developer.xamarin.com/guides/xamarin-forms/working-with/behaviors/