C#中的yield return與Unity中的Coroutine（協程）（下）

Unity中的Coroutine（協程）

估計熟悉Unity的人看過或者用過StartCoroutine()

假設咱們在場景中有一個UGUI組件， Image：

將如下代碼綁定到Image

 1 using UnityEngine;
 2 using System.Collections;
 3 using System.Threading;
 4 using UnityEngine.UI;
 5 
 6 public class CoroutineDemo : MonoBehaviour {
 7 
 8     // Use this for initialization
 9     void Start () {
10     
11         Debug.Log (Thread.CurrentThread.Name + ": Start begin. fCount=" +  + Time.renderedFrameCount);
12 
13 
14         this.StartCoroutine (exeuteCoroutine());
15     }
16     
17     // Update is called once per frame
18     void Update () {
19         
20         Debug.Log (Thread.CurrentThread.Name + ": Update(): fCount=" + Time.renderedFrameCount);
21     }
22 
23      
24     public IEnumerator exeuteCoroutine(){
25         Debug.Log (Thread.CurrentThread.Name + ": Before yield return A, fCount=" + Time.renderedFrameCount);
26         //yield return new WaitForSeconds(1);
27         yield return "A";
28 //        yield return "C";
29 //        yield return "D";
30         Debug.LogError (Thread.CurrentThread.Name + ": After yield return A, fCount=" + Time.renderedFrameCount);
31     }
32 
33     IEnumerator LoadImage()
34     {
35         WWW www=new WWW("http://pic89.nipic.com/file/20160211/22571617_214730734684_2.jpg");
36         Image img = this.gameObject.GetComponent<Image> ();
37 
38         Debug.Log("Before yield return: " + www.url + " is done? " + www.isDone + ", rf=" + Time.renderedFrameCount);
39 
40         yield return www;
41 
42         Debug.Log("After yield return, " + www.url + " is done? " + www.isDone + ", rf=" + Time.renderedFrameCount);
43         Rect spriteRect = new Rect (0, 0, www.texture.width, www.texture.height);
44         Sprite imageSprite = Sprite.Create (www.texture, spriteRect, new Vector2 (0.5f, 0.5f));
45         img.sprite = imageSprite;
46 
47     }
48 }

View Code

運行以後日誌輸出（Error 日誌是爲了明顯，才這麼打的）：

 

fCount 表明的是當前已經渲染的幀數，發現， yield return 以後的代碼， 是在yield return 以後的一幀執行的。

若是yield return 以後換成 new WaitForSeconds(1); yield以後的代碼就在1秒後執行。

看一下MonoBehaviour的生命週期：

 

 

發現， 在StartCortinue()傳入的方法中， 能夠yield return 的類型有：

yield return null;

yield return WaitForSeconds(); (實際上， 繼承自 YieldInstruction的均可以）

yield return WWW;

若是將例子中的代碼改爲加載圖片：

 

1     void Start () {  
3         Debug.Log (Thread.CurrentThread.ManagedThreadId + ": Start begin. fCount=" +  + Time.renderedFrameCount);
6         this.StartCoroutine (LoadImage());
7     }

 

 1     IEnumerator LoadImage()
 2     {
 3         WWW www=new WWW("http://pic89.nipic.com/file/20160211/22571617_214730734684_2.jpg");
 4         Image img = this.gameObject.GetComponent<Image> ();
 5 
 6         Debug.Log("Before yield return: " + www.url + " is done? " + www.isDone + ", rf=" + Time.renderedFrameCount);
 7 
 8         yield return www;
 9 
10         Debug.Log("After yield return, " + www.url + " is done? " + www.isDone + ", rf=" + Time.renderedFrameCount);
11         Rect spriteRect = new Rect (0, 0, www.texture.width, www.texture.height);
12         Sprite imageSprite = Sprite.Create (www.texture, spriteRect, new Vector2 (0.5f, 0.5f));
13         img.sprite = imageSprite;
14 
15     }

 

經過輸出日誌， 你會發現， yield return www;以後的代碼， 是在www.isDone以後， 也就是圖片加載完畢以後才執行的！

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:38)
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
CoroutineDemo:Start() (at Assets/Scripts/CoroutineDemo.cs:14)

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:42)

總結：

yield return 搭配上WaitForSecond, WWW， 能夠達到延時執行的效果。

可是， 特別注意的是， StartCoroutine()並無開啓新的線程來執行， 仍是執行在與Start(), Update（）相同的主線程中！