Yield使用方法

matthew_1983

C#中Yield使用方法小结，可能理解的不正确，后续修改。

yield return可以看做是一种特殊的return，会返回到父类继续执行，但是yield return后面的类型或方法会有一个执行条件，当条件满足时会回调包含yield的子函数，例如下面代码

例1：

1. void Start () {
   
2.         print("Starting:" + Time.time);
   
3.         StartCoroutine(WaitAnPrint(2.0F));
   
4.         print("Before WaiAndPrint:" + Time.time);
   
5.     }
   
6. IEnumerator WaitAndPrint(float waitTime)
   
7.     {
   
8.         yield return new WaitForSeconds(waitTime);
   
9.         print("WaitAndPrint:" + Time.time);    
   
10.     }

在执行yield return new WaitForSeconds(waitTime)时暂停的条件没有满足，故返回到start函数中继续执行，直到满足条件后再回调WaitAndPrint,所以输出为：

1. Starting:0
   
2. Before WaiAndPrint:0
   
3. WaitAndPrint:2.12291

例2:

1. IEnumerator Start()
   
2.     {
   
3.         print("starting:" + Time.time);
   
4.         yield return StartCoroutine(WaitAndPrint(2.0F));
   
5.         print("done:" + Time.time);
   
6.     }
   
7. IEnumerator WaitAndPrint(float waitTime)
   
8.     {
   
9.         yield return new WaitForSeconds(waitTime);
   
10.         print("WaitAndPrint:" + Time.time);    
    
11.     }

因为start为顶级函数，所以会阻塞在这里，直到StartCoroutine(WaitAndPrint(2.0F))执行完毕，输出为：

1. starting:0
   
2. WaitAndPrint:2.00315
   
3. done:2.00315