com.unity.uiextensions/Runtime/Scripts/Utilities/UIHighlightable.cs

/// Credit SimonDarksideJ
/// Sourced from - Issue Proposal #153

using UnityEngine.EventSystems;

namespace UnityEngine.UI.Extensions
{
    [AddComponentMenu("UI/Extensions/UI Highlightable Extension")]
    [RequireComponent(typeof(RectTransform), typeof(Graphic))]
    public class UIHighlightable : MonoBehaviour, IPointerEnterHandler, IPointerExitHandler, IPointerDownHandler, IPointerUpHandler
    {
        private Graphic m_Graphic;
        private bool m_Highlighted;
        private bool m_Pressed;

        [System.Serializable]
        public class InteractableChangedEvent : Events.UnityEvent<bool> { }
        [System.Serializable]
        public class HighlightChangedEvent : Events.UnityEvent<bool> { }
        [System.Serializable]
        public class PressChangedEvent : Events.UnityEvent<bool> { }

        [SerializeField][Tooltip("Can this panel be interacted with or is it disabled? (does not affect child components)")]
        private bool m_Interactable = true;
        [SerializeField][Tooltip("Does the panel remain in the pressed state when clicked? (default false)")]
        private bool m_ClickToHold;

        public bool Interactable
        {
            get { return m_Interactable; }
            set
            {
                m_Interactable = value;
                HighlightInteractable(m_Graphic);
                OnInteractableChanged.Invoke(m_Interactable);

                if(!m_Interactable)
                {
                    if(m_Highlighted)
                    {
                        m_Highlighted = false;
                        OnHighlightChanged.Invoke(false);
                    }

                    if(m_Pressed)
                    {
                        m_Pressed = false;
                        OnPressChanged.Invoke(false);
                    }
                }
            }
        }

        public bool ClickToHold
        {
            get { return m_ClickToHold; }
            set
            {
                m_ClickToHold = value;

                if(!m_ClickToHold && m_Pressed)
                {
                    m_Pressed = false;
                    OnPressChanged.Invoke(false);
                }
            }
        }

        public bool Highlighted
        {
            get { return m_Highlighted; }
            set
            {
                if(m_Highlighted != value)
                {
                    m_Highlighted = value;
                    HighlightInteractable(m_Graphic);
                    if(m_Interactable)
                    {
                        OnHighlightChanged.Invoke(m_Highlighted);
                    }
                }
            }
        }

        public bool Pressed
        {
            get { return m_Pressed; }
            set
            {
                if(m_Pressed != value)
                {
                    m_Pressed = value;
                    m_Graphic.color = (m_Pressed ? PressedColor : NormalColor);
                    if(m_Interactable)
                    {
                        OnPressChanged.Invoke(m_Pressed);
                    }
                }
            }
        }

        [Tooltip("The default color for the panel")]
        public Color NormalColor = Color.grey;
        [Tooltip("The color for the panel when a mouse is over it or it is in focus")]
        public Color HighlightedColor = Color.yellow;
        [Tooltip("The color for the panel when it is clicked/held")]
        public Color PressedColor = Color.green;
        [Tooltip("The color for the panel when it is not interactable (see Interactable)")]
        public Color DisabledColor = Color.gray;

        [Tooltip("Event for when the panel is enabled / disabled, to enable disabling / enabling of child or other gameobjects")]
        public InteractableChangedEvent OnInteractableChanged;
        [Tooltip("Event for when the panel highlight state is activated or deactivated")]
        public HighlightChangedEvent OnHighlightChanged;
        [Tooltip("Event for when the panel press state is activated or deactivated")]
        public PressChangedEvent OnPressChanged;

        void Awake()
        {
            m_Graphic = GetComponent<Graphic>();
        }

        public void OnPointerEnter(PointerEventData eventData)
        {
            if (Interactable && !m_Pressed)
            {
                m_Highlighted = true;
                m_Graphic.color = HighlightedColor;
                OnHighlightChanged.Invoke(true);
            }
        }

        public void OnPointerExit(PointerEventData eventData)
        {
            if (Interactable && !m_Pressed)
            {
                m_Highlighted = false;
                m_Graphic.color = NormalColor;
                OnHighlightChanged.Invoke(false);
            }
        }

        public void OnPointerDown(PointerEventData eventData)
        {
            if (Interactable)
            {
                m_Graphic.color = PressedColor;
                if (ClickToHold)
                {
                    if(m_Pressed)
                    {
                        m_Pressed = false;
                    }
                    else
                    {
                        m_Pressed = true;
                        OnPressChanged.Invoke(true);
                    }
                }
                else
                {
                    OnPressChanged.Invoke(true);
                }
            }
        }

        public void OnPointerUp(PointerEventData eventData)
        {
            if(!m_Pressed)
            {
                HighlightInteractable(m_Graphic);
                if(m_Interactable)
                {
                    OnPressChanged.Invoke(false);
                }
            }
        }

        private void HighlightInteractable(Graphic graphic)
        {
            if (m_Interactable)
            {
                if (m_Highlighted)
                {
                    graphic.color = HighlightedColor;
                }
                else
                {
                    graphic.color = NormalColor;
                }
            }
            else
            {
                graphic.color = DisabledColor;
            }
        }

#if UNITY_EDITOR
        private void OnValidate()
        {
            HighlightInteractable(GetComponent<Graphic>());
        }
#endif
    }
}