UGUI Toggle 实现图片切换

用Toggle 来实现选中状态一张图片不选中状态另一张图片时，Transition 选择Sprite Swap 会出现IsOn状态下两张图片叠加。

解决思路：背景图片IsOn状态时将其alpha值设为0。

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;


public class ToggleIsOn : MonoBehaviour
{
    private Toggle toggle;
    //未选中图片，Background
    private Image unselectedImage;
    //选中图片，Checkmark
    private Image selectedImage;
    private void Start()
    {
        toggle = GetComponent<Toggle>();
        unselectedImage = toggle.targetGraphic as Image;
        selectedImage = toggle.graphic as Image;
        toggle.onValueChanged.AddListener(OnToggleValueChanged);
    }
    private void OnToggleValueChanged(bool isOn)
    {
        if (isOn)
        {
            unselectedImage.color = new Color(255,255,255,0);
        }
        else
        {
            unselectedImage.color = new Color(255,255,255,255);
        }
    }
}