Unity3D协程Coroutine解析
本文只是从Unity的角度去分析理解协程的内部运行原理,而不是从C#底层的语法实现来介绍(后续有需要再进行介绍),一共分为三部分:
1. 线程(Thread)和协程(Coroutine)
使用协程的作用一共有两点:1)延时(等待)一段时间执行代码;2)等某个操作完成之后再执行后面的代码。总结起来就是一句话:控制代码在特定的时机执行。 很多初学者,都会下意识地觉得协程是异步执行的,都会觉得协程是C# 线程的替代品,是Unity不使用线程的解决方案。 所以首先,请你牢记:协程不是线程,也不是异步执行的。协程和 MonoBehaviour 的 Update函数一样也是在MainThread中执行的。使用协程你不用考虑同步和锁的问题。
2. Unity中协程的执行原理
UnityGems.com给出了协程的定义: A coroutine is a function that is executed partially and, presuming suitable conditions are met, will be resumed at some point in the future until its work is done. 即协程是一个分部执行,遇到条件(yield return 语句)会挂起,直到条件满足才会被唤醒继续执行后面的代码。 Unity在每一帧(Frame)都会去处理对象上的协程。Unity主要是在Update后去处理协程(检查协程的条件是否满足),但也有写特例: 从上图的剖析就明白,协程跟Update()其实一样的,都是Unity每帧对会去处理的函数(如果有的话)。如果MonoBehaviour 是处于激活(active)状态的而且yield的条件满足,就会协程方法的后面代码。还可以发现:如果在一个对象的前期调用协程,协程会立即运行到第一个 yield return 语句处,如果是 yield return null ,就会在同一帧再次被唤醒。如果没有考虑这个细节就会出现一些奇怪的问题『1』。 『1』注 图和结论都是从UnityGems.com 上得来的,经过下面的验证发现与实际不符,D.S.Qiu用的是Unity 4.3.4f1 进行测试的。 经过测试验证,协程至少是每帧的LateUpdate()后去运行。
下面使用 yield return new WaitForSeconds(1f); 在Start,Update 和 LateUpdate 中分别进行测试:
using UnityEngine; using System.Collections; public class TestCoroutine : MonoBehaviour { private bool isStartCall = false; //Makesure Update() and LateUpdate() Log only once private bool isUpdateCall = false; private bool isLateUpdateCall = false; // Use this for initialization void Start () { if (!isStartCall) { Debug.Log("Start Call Begin"); StartCoroutine(StartCoutine()); Debug.Log("Start Call End"); isStartCall = true; } } IEnumerator StartCoutine() { Debug.Log("This is Start Coroutine Call Before"); yield return null; Debug.Log("This is Start Coroutine Call After"); } // Update is called once per frame void Update () { if (!isUpdateCall) { Debug.Log("Update Call Begin"); StartCoroutine(UpdateCoutine()); Debug.Log("Update Call End"); isUpdateCall = true; } } IEnumerator UpdateCoutine() { Debug.Log("This is Update Coroutine Call Before"); yield return null; Debug.Log("This is Update Coroutine Call After"); } void LateUpdate() { if (!isLateUpdateCall) { Debug.Log("LateUpdate Call Begin"); StartCoroutine(LateCoutine()); Debug.Log("LateUpdate Call End"); isLateUpdateCall = true; } } IEnumerator LateCoutine() { Debug.Log("This is Late Coroutine Call Before"); yield return null; Debug.Log("This is Late Coroutine Call After"); } }得到日志输入结果如下:
然后将yield return new WaitForSeconds(1f);改为 yield return null; 发现日志输入结果和上面是一样的,没有出现上面说的情况.
MonoBehaviour 没有针对特定的协程提供Stop方法,其实不然,可以通过MonoBehaviour enabled = false 或者 gameObject.active = false 就可以停止协程的执行『2』。
经过验证,『2』的结论也是错误的,正确的结论是,MonoBehaviour.enabled = false 协程会照常运行,但 gameObject.SetActive(false) 后协程却全部停止,即使在Inspector把 gameObject 激活还是没有继续执行:
using UnityEngine; using System.Collections; public class TestCoroutine : MonoBehaviour { private bool isStartCall = false; //Makesure Update() and LateUpdate() Log only once private bool isUpdateCall = false; private bool isLateUpdateCall = false; // Use this for initialization void Start () { if (!isStartCall) { Debug.Log("Start Call Begin"); StartCoroutine(StartCoutine()); Debug.Log("Start Call End"); isStartCall = true; } } IEnumerator StartCoutine() { Debug.Log("This is Start Coroutine Call Before"); yield return new WaitForSeconds(1f); Debug.Log("This is Start Coroutine Call After"); } // Update is called once per frame void Update () { if (!isUpdateCall) { Debug.Log("Update Call Begin"); StartCoroutine(UpdateCoutine()); Debug.Log("Update Call End"); isUpdateCall = true; this.enabled = false; //this.gameObject.SetActive(false); } } IEnumerator UpdateCoutine() { Debug.Log("This is Update Coroutine Call Before"); yield return new WaitForSeconds(1f); Debug.Log("This is Update Coroutine Call After"); yield return new WaitForSeconds(1f); Debug.Log("This is Update Coroutine Call Second"); } void LateUpdate() { if (!isLateUpdateCall) { Debug.Log("LateUpdate Call Begin"); StartCoroutine(LateCoutine()); Debug.Log("LateUpdate Call End"); isLateUpdateCall = true; } } IEnumerator LateCoutine() { Debug.Log("This is Late Coroutine Call Before"); yield return null; Debug.Log("This is Late Coroutine Call After"); } }先在Update中调用 this.enabled = false; 得到的结果:
然后把 this.enabled = false; 注释掉,换成 this.gameObject.SetActive(false); 得到的结果如下:
整理得到 :通过设置MonoBehaviour脚本的enabled对协程是没有影响的,但如果 gameObject.SetActive(false) 则已经启动的协程则完全停止了,即使在Inspector把gameObject 激活还是没有继续执行。也就说协程虽然是在MonoBehvaviour启动的(StartCoroutine)但是协程函数的地位完全是跟MonoBehaviour是一个层次的,不受MonoBehaviour的状态影响,但跟MonoBehaviour脚本一样受gameObject 控制,也应该是和MonoBehaviour脚本一样每帧“轮询” yield 的条件是否满足。
yield 后面可以有的表达式:
a) null - the coroutine executes the next time that it is eligible
b) WaitForEndOfFrame - the coroutine executes on the frame, after all of the rendering and GUI is complete
c) WaitForFixedUpdate - causes this coroutine to execute at the next physics step, after all physics is calculated
d) WaitForSeconds - causes the coroutine not to execute for a given game time period
e) WWW - waits for a web request to complete (resumes as if WaitForSeconds or null)
f) 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影响,当Time.timeScale = 0f 时,yield return new WaitForSecond(x) 将不会满足。
3. IEnumerator & Coroutine
协程其实就是一个IEnumerator(迭代器),IEnumerator 接口有两个方法 Current 和 MoveNext() ,前面介绍的TaskManager就是利用者两个方法对协程进行了管理,这里在介绍一个协程的交叉调用类 Hijack:
using System; using System.Collections.Generic; using System.Linq; using UnityEngine; using System.Collections; using UnityEngine.UI; [RequireComponent(typeof(Text))] public class HiJack : MonoBehaviour { //This will hold the counting up coroutine IEnumerator _countUp; //This will hold the counting down coroutine IEnumerator _countDown; //This is the coroutine we are currently //hijacking IEnumerator _current; //A value that will be updated by the coroutine //that is currently running int value = 0; void Start() { //Create our count up coroutine _countUp = CountUp(); //Create our count down coroutine _countDown = CountDown(); //Start our own coroutine for the hijack StartCoroutine(DoHijack()); } void Update() { //Show the current value on the screen GetComponent().text = value.ToString (); } void OnGUI() { //Switch between the different functions if(GUILayout.Button("Switch functions")) { if(_current == _countUp) _current = _countDown; else _current = _countUp; } } IEnumerator DoHijack() { while(true) { //Check if we have a current coroutine and MoveNext on it if we do if(_current != null && _current.MoveNext()) { //Return whatever the coroutine yielded, so we will yield the //same thing yield return _current.Current; } else //Otherwise wait for the next frame yield return null; } } IEnumerator CountUp() { //We have a local increment so the routines //get independently faster depending on how //long they have been active float increment = 0; while(true) { //Exit if the Q button is pressed if(Input.GetKey(KeyCode.Q)) break; increment+=Time.deltaTime; value += Mathf.RoundToInt(increment); yield return null; } } IEnumerator CountDown() { float increment = 0f; while(true) { if(Input.GetKey(KeyCode.Q)) break; increment+=Time.deltaTime; value -= Mathf.RoundToInt(increment); //This coroutine returns a yield instruction yield return new WaitForSeconds(0.1f); } } }上面的代码实现是两个协程交替调用,对有这种需求来说实在太妙了。
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