unity3d之简单的时钟倒计时demo

输入结束时间，开始倒计时，时间差不超过一天，附上代码：(关于个位数显示，加个判断如果小于10 显示的字符串加上0)

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using System;
 public class CountdownDemo : MonoBehaviour {

     public Text hour;
     public Text min;
     public Text sec;
     public InputField timestr;
     public Coroutine cc;
     private DateTime endtime;

     IEnumerator countdown()
     {
         while (true)
         {
             TimeSpan temp = endtime - DateTime.Now;
             hour.text = temp.Hours.ToString();
             min.text = temp.Minutes.ToString();
             sec.text = temp.Seconds.ToString();
             yield return new WaitForSeconds();
         }
     }

     void OnGUI()
     {
         if (GUI.Button(new Rect(, , , ), "start"))
         {
             endtime = Convert.ToDateTime(timestr.text);
             cc = StartCoroutine(countdown());
         }
         if (GUI.Button(new Rect(, , , ), "end"))
         {
             this.StopCoroutine(cc);
         }
     }
 }