Monobehaviour的函數執行順序圖
yield後面可以加的表達式
- null - then coroutine executes the next time that it is eligible; 暫停協同程序，下一幀在繼續執行
- WaitForEndOfFrame - the coroutine executes on the frame,after all of the rendering and GUI is complete
- WaitForFixedUpdate - causes this coroutine to execute at the next physics step, after all physics is calcuated
- WaitForSeconds - cause the corotine not to execute for a iven game time period
- WWW - waits for a web request to complete (resumes as if AwaiForSeconds or null)
- Another coroutine - in which case the new coroutine will run to completion before the yielder is resumed
值得注意的是WaitForSeconds()受Time.timeScale影響，當Time.timeScale = 0f時，yield return new WaitForSecond(x)將不會滿足。
IEnumerator & Coroutine
協程其實就是一個迭代器，IEnumerator接口有兩個方法Current和MoveNext(),只有當MoveNext()返回true時纔會訪問Current,否則回報錯，迭代器犯法運行到yield return語句時，會返回一個expression表達式並保留當前代碼中的位置。