UnityUI加载进度条

初学者的写法：

System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;
public class NewBehaviourScript : MonoBehaviour {
    public float UI_Wight;
    public float UI_Height;
    float process;
    float _process;
    void Start ()
    {
              
    }
     void Update ()
     {
              
     }
    void OnGUI()
    {
        GUI.color = Color.red;
        if(GUI.Button(new Rect(Screen.width / 2 - UI_Wight / 2, Screen.height / 2 - UI_Height / 2, UI_Wight, UI_Height),"开始游戏"))
        {
            StartCoroutine("LoadSceneFromBtn");
        }
        GUILayout.Label("场景加载进度" + _process *100 +"%");
    }

    IEnumerator LoadSceneFromBtn()
    {
         AsyncOperation ao= SceneManager.LoadSceneAsync(1);
        ao.allowSceneActivation = false;
        while (_process<1.0f)
        {
            process =ao.progress;
            if (_process >= 0.9f)
            {
               _process= Mathf.MoveTowards(_process, 1.0f, 0.01f);
            }
            else
            {
               _process= Mathf.MoveTowards(_process, process, 0.01f);
            }
            yield return 0;
        }
        ao.allowSceneActivation = true;
    }
}