C#中的yield return与Unity中的Coroutine（协程）（下）

Unity中的Coroutine（协程）

估计熟悉Unity的人看过或者用过StartCoroutine()

假设我们在场景中有一个UGUI组件， Image：

将以下代码绑定到Image

 using UnityEngine;
 using System.Collections;
 using System.Threading;
 using UnityEngine.UI;

 public class CoroutineDemo : MonoBehaviour {

     // Use this for initialization
     void Start () {

         Debug.Log (Thread.CurrentThread.Name + ": Start begin. fCount=" +  + Time.renderedFrameCount);

         this.StartCoroutine (exeuteCoroutine());
     }

     // Update is called once per frame
     void Update () {

         Debug.Log (Thread.CurrentThread.Name + ": Update(): fCount=" + Time.renderedFrameCount);
     }

     public IEnumerator exeuteCoroutine(){
         Debug.Log (Thread.CurrentThread.Name + ": Before yield return A, fCount=" + Time.renderedFrameCount);
         //yield return new WaitForSeconds(1);
         yield return "A";
 //        yield return "C";
 //        yield return "D";
         Debug.LogError (Thread.CurrentThread.Name + ": After yield return A, fCount=" + Time.renderedFrameCount);
     }

     IEnumerator LoadImage()
     {
         WWW www=new WWW("http://pic89.nipic.com/file/20160211/22571617_214730734684_2.jpg");
         Image img = this.gameObject.GetComponent<Image> ();

         Debug.Log("Before yield return: " + www.url + " is done? " + www.isDone + ", rf=" + Time.renderedFrameCount);

         yield return www;

         Debug.Log("After yield return, " + www.url + " is done? " + www.isDone + ", rf=" + Time.renderedFrameCount);
         Rect spriteRect = new Rect (, , www.texture.width, www.texture.height);
         Sprite imageSprite = Sprite.Create (www.texture, spriteRect, new Vector2 (0.5f, 0.5f));
         img.sprite = imageSprite;

     }
 }

运行之后日志输出（Error 日志是为了明显，才这么打的）：

fCount 代表的是当前已经渲染的帧数，发现， yield return 之后的代码， 是在yield return 之后的一帧执行的。

如果yield return 之后换成 new WaitForSeconds(1); yield之后的代码就在1秒后执行。

看一下MonoBehaviour的生命周期：

发现， 在StartCortinue()传入的方法中， 可以yield return 的类型有：

yield return null;

yield return WaitForSeconds(); (实际上， 继承自 YieldInstruction的都可以）

yield return WWW;

如果将例子中的代码改成加载图片：

     void Start () {
         Debug.Log (Thread.CurrentThread.ManagedThreadId + ": Start begin. fCount=" +  + Time.renderedFrameCount);
         this.StartCoroutine (LoadImage());
     }

     IEnumerator LoadImage()
     {
         WWW www=new WWW("http://pic89.nipic.com/file/20160211/22571617_214730734684_2.jpg");
         Image img = this.gameObject.GetComponent<Image> ();

         Debug.Log("Before yield return: " + www.url + " is done? " + www.isDone + ", rf=" + Time.renderedFrameCount);

         yield return www;

         Debug.Log("After yield return, " + www.url + " is done? " + www.isDone + ", rf=" + Time.renderedFrameCount);
         Rect spriteRect = new Rect (, , www.texture.width, www.texture.height);
         Sprite imageSprite = Sprite.Create (www.texture, spriteRect, new Vector2 (0.5f, 0.5f));
         img.sprite = imageSprite;

     }

通过输出日志， 你会发现， yield return www;之后的代码， 是在www.isDone之后， 也就是图片加载完毕之后才执行的！

Before yield return: http://pic89.nipic.com/file/20160211/22571617_214730734684_2.jpg is done? False, rf=1
UnityEngine.Debug:Log(Object)
<LoadImage>c__Iterator6:MoveNext() (at Assets/Scripts/CoroutineDemo.cs:)
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
CoroutineDemo:Start() (at Assets/Scripts/CoroutineDemo.cs:)

After yield return, http://pic89.nipic.com/file/20160211/22571617_214730734684_2.jpg is done? True, rf=34
UnityEngine.Debug:Log(Object)
<LoadImage>c__Iterator6:MoveNext() (at Assets/Scripts/CoroutineDemo.cs:)

总结：

yield return 搭配上WaitForSecond, WWW， 可以达到延时执行的效果。

但是， 特别注意的是， StartCoroutine()并没有开启新的线程来执行， 还是执行在与Start(), Update（）相同的主线程中！