HorizontalArrowKey.cs

/* By Thomas "noio" van den Berg

Add this script to the UI.Buttons that form
a left/right arrow pair. For each button,
drag the *other* button into the "other" field.

It requires that your buttons are animated using
"Transition: Animation", (not Sprite Swap) with an
animator that has the default Trigger parameters defined
("Normal", "Highlighted", "Pressed")
*/

using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System.Collections;

public class HorizontalArrowKey : MonoBehaviour, ISelectHandler, IDeselectHandler, IPointerExitHandler
{
    public enum Direction
    {
        Left,
        Right
    }

    public Direction direction;
    public HorizontalArrowKey other;

    bool _selected;

    Rewired.Player _rewired;
    Animator _animator;
    Button _button;

    void Awake()
    {
        _button = Require.Component<Button>(this);
        _rewired = Rewired.ReInput.players.GetPlayer(0);
        _animator = Require.Component<Animator>(this);
    }

    void Update()
    {
        if (_selected || other._selected)
        {
            if (direction == Direction.Left && _rewired.GetNegativeButtonDown(RewiredAxis.Horizontal))
            {
                StartCoroutine(Press());
            }
            else if (direction == Direction.Right && _rewired.GetButtonDown(RewiredAxis.Horizontal))
            {
                StartCoroutine(Press());
            }
        }
    }

    IEnumerator Press()
    {
        _button.onClick.Invoke();
        _animator.ResetTrigger("Normal");
        _animator.ResetTrigger("Highlighted");
        _animator.SetTrigger("Pressed");
        float elapsed = 0;
        while (elapsed < 0.1f)
        {
            elapsed += Time.unscaledDeltaTime;
            yield return null;
        }
        _animator.SetTrigger("Highlighted");
    }

    public void OnSelect(BaseEventData eventData)
    {
        _selected = true;
        //  _animator.SetTrigger("Highlighted");
        other._animator.ResetTrigger("Normal");
        other._animator.SetTrigger("Highlighted");
    }

    public void OnDeselect(BaseEventData eventData)
    {
        _selected = false;
        // _animator.SetTrigger("Normal");
        other._animator.SetTrigger("Normal");
    }

    public void OnPointerExit(PointerEventData eventData)
    {
        if (other._selected)
        {
            _animator.ResetTrigger("Normal");
            _animator.SetTrigger("Highlighted");
        }
    }
}