Unity 双击Esc或者返回退出游戏,有文字提示

第一次点击Esc或者返回,显示提示文字"再次按下返回键退出游戏",在文字消失之前再次点击Esc或者返回,退出游戏.

此脚本挂在Text文字提示上:

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
public class ExitGame : MonoBehaviour
{
    [Tooltip("ExitMessage拖进来")]
    Text ExitMessageObj;
    float fadingSpeed = 1;
    bool fading;
    float startFadingTimep;
    Color originalColor;
    Color transparentColor;
    string sss;

    void Start()
    {
        ExitMessageObj = this.GetComponent<Text>();
        originalColor = ExitMessageObj.color;
        transparentColor = originalColor;
        transparentColor.a = 0;
        ExitMessageObj.text = "再次按下返回键退出游戏";
        ExitMessageObj.color = transparentColor;
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Escape))
        {
            if (startFadingTimep == 0)
            {
                ExitMessageObj.color = originalColor;
                startFadingTimep = Time.time;
                fading = true;
            }
            else
            {               44                 Application.Quit();//退出游戏
            }
        }
        if (fading)
        {
            ExitMessageObj.color = Color.Lerp(originalColor, transparentColor, (Time.time - startFadingTimep) * fadingSpeed);
            if (ExitMessageObj.color.a < 2.0 / 255)
            {
                ExitMessageObj.color = transparentColor;
                startFadingTimep = 0;
                fading = false;
            }
        }
    }
}