geometry-tower-defense/Assets/GameMain/Scripts/UI/CommonButton.cs

using UnityEngine;
using UnityEngine.Events;
using UnityEngine.EventSystems;
using UnityEngine.Serialization;

namespace GeometryTD.UI
{
    public class CommonButton : MonoBehaviour, IPointerEnterHandler, IPointerExitHandler, IPointerDownHandler,
        IPointerUpHandler
    {
        private const float FadeTime = 0.3f;
        private const float OnHoverAlpha = 0.7f;
        private const float OnClickAlpha = 0.6f;

        [FormerlySerializedAs("m_OnHover")] [SerializeField]
        private UnityEvent _onHover = null;

        [FormerlySerializedAs("m_OnClick")] [SerializeField]
        private UnityEvent _onClick = null;

        [SerializeField] private UnityEvent _onHoverEnd = null;

        [SerializeField] private bool _allowFade = true;

        private CanvasGroup _canvasGroup = null;

        private void Awake()
        {
            _canvasGroup = gameObject.GetOrAddComponent<CanvasGroup>();
        }

        private void OnDisable()
        {
            _canvasGroup.alpha = 1f;
        }

        public void OnPointerEnter(PointerEventData eventData)
        {
            if (eventData.button != PointerEventData.InputButton.Left)
            {
                return;
            }

            StopAllCoroutines();
            if (_allowFade)
                StartCoroutine(_canvasGroup.FadeToAlpha(OnHoverAlpha, FadeTime));
            _onHover.Invoke();
        }

        public void OnPointerExit(PointerEventData eventData)
        {
            if (eventData.button != PointerEventData.InputButton.Left)
            {
                return;
            }

            StopAllCoroutines();
            if (_allowFade)
                StartCoroutine(_canvasGroup.FadeToAlpha(1f, FadeTime));
            _onHoverEnd?.Invoke();
        }

        public void OnPointerDown(PointerEventData eventData)
        {
            if (eventData.button != PointerEventData.InputButton.Left)
            {
                return;
            }

            _canvasGroup.alpha = OnClickAlpha;
            _onClick.Invoke();
        }

        public void OnPointerUp(PointerEventData eventData)
        {
            if (eventData.button != PointerEventData.InputButton.Left)
            {
                return;
            }

            _canvasGroup.alpha = OnHoverAlpha;
        }
    }
}