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()

假設我們在場景中有一個UGUI組件， Image：

將以下代碼綁定到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 (0, 0, www.texture.width, www.texture.height);
        Sprite imageSprite = Sprite.Create (www.texture, spriteRect, new Vector2 (0.5f, 0.5f));
        img.sprite = imageSprite;

    }
}

運行之后日志輸出（Error 日志是為了明顯，才這么打的）：

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fCount 代表的是當前已經渲染的幀數，發現， yield return 之后的代碼， 是在yield return 之后的一幀執行的。

如果yield return 之后換成 new WaitForSeconds(1);?yield之后的代碼就在1秒后執行。

看一下MonoBehaviour的生命周期：

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

yield return null;

yield return WaitForSeconds(); (實際上， 繼承自 YieldInstruction的都可以）

yield return WWW;

如果將例子中的代碼改成加載圖片：

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

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    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 (0, 0, www.texture.width, www.texture.height);
        Sprite imageSprite = Sprite.Create (www.texture, spriteRect, new Vector2 (0.5f, 0.5f));
        img.sprite = imageSprite;

    }

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通過輸出日志， 你會發現， yield return www;之后的代碼， 是在www.isDone之后， 也就是圖片加載完畢之后才執行的！

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， 可以達到延時執行的效果。

但是， 特別注意的是， StartCoroutine()并沒有開啟新的線程來執行， 還是執行在與Start(), Update（）相同的主線程中！

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