Unity3D協(xié)程Coroutine解析
本文只是從Unity的角度去分析理解協(xié)程的內(nèi)部運(yùn)行原理，而不是從C#底層的語法實(shí)現(xiàn)來介紹（后續(xù)有需要再進(jìn)行介紹），一共分為三部分：
1. 線程（Thread）和協(xié)程（Coroutine）
使用協(xié)程的作用一共有兩點(diǎn)：1）延時(shí)（等待）一段時(shí)間執(zhí)行代碼；2）等某個(gè)操作完成之后再執(zhí)行后面的代碼。總結(jié)起來就是一句話：控制代碼在特定的時(shí)機(jī)執(zhí)行。 很多初學(xué)者，都會(huì)下意識(shí)地覺得協(xié)程是異步執(zhí)行的，都會(huì)覺得協(xié)程是C# 線程的替代品，是Unity不使用線程的解決方案。 所以首先，請你牢記：協(xié)程不是線程，也不是異步執(zhí)行的。協(xié)程和 MonoBehaviour 的 Update函數(shù)一樣也是在MainThread中執(zhí)行的。使用協(xié)程你不用考慮同步和鎖的問題。
2. Unity中協(xié)程的執(zhí)行原理
UnityGems.com給出了協(xié)程的定義： 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. 即協(xié)程是一個(gè)分部執(zhí)行，遇到條件（yield return 語句）會(huì)掛起，直到條件滿足才會(huì)被喚醒繼續(xù)執(zhí)行后面的代碼。 Unity在每一幀（Frame）都會(huì)去處理對(duì)象上的協(xié)程。Unity主要是在Update后去處理協(xié)程（檢查協(xié)程的條件是否滿足），但也有寫特例： 從上圖的剖析就明白，協(xié)程跟Update()其實(shí)一樣的，都是Unity每幀對(duì)會(huì)去處理的函數(shù)（如果有的話）。如果MonoBehaviour 是處于激活（active）狀態(tài)的而且yield的條件滿足，就會(huì)協(xié)程方法的后面代碼。還可以發(fā)現(xiàn)：如果在一個(gè)對(duì)象的前期調(diào)用協(xié)程，協(xié)程會(huì)立即運(yùn)行到第一個(gè) yield return 語句處，如果是 yield return null ，就會(huì)在同一幀再次被喚醒。如果沒有考慮這個(gè)細(xì)節(jié)就會(huì)出現(xiàn)一些奇怪的問題『1』。 『1』注 圖和結(jié)論都是從UnityGems.com 上得來的，經(jīng)過下面的驗(yàn)證發(fā)現(xiàn)與實(shí)際不符，D.S.Qiu用的是Unity 4.3.4f1 進(jìn)行測試的。 經(jīng)過測試驗(yàn)證，協(xié)程至少是每幀的LateUpdate()后去運(yùn)行。
下面使用 yield return new WaitForSeconds(1f); 在Start,Update 和 LateUpdate 中分別進(jìn)行測試：
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");
}
}
得到日志輸入結(jié)果如下：
然后將yield return new WaitForSeconds(1f);改為 yield return null; 發(fā)現(xiàn)日志輸入結(jié)果和上面是一樣的，沒有出現(xiàn)上面說的情況.
MonoBehaviour 沒有針對(duì)特定的協(xié)程提供Stop方法，其實(shí)不然，可以通過MonoBehaviour enabled = false 或者 gameObject.active = false 就可以停止協(xié)程的執(zhí)行『2』。
經(jīng)過驗(yàn)證，『2』的結(jié)論也是錯(cuò)誤的，正確的結(jié)論是，MonoBehaviour.enabled = false 協(xié)程會(huì)照常運(yùn)行，但 gameObject.SetActive(false) 后協(xié)程卻全部停止，即使在Inspector把 gameObject 激活還是沒有繼續(xù)執(zhí)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中調(diào)用 this.enabled = false; 得到的結(jié)果：
然后把 this.enabled = false; 注釋掉，換成 this.gameObject.SetActive(false); 得到的結(jié)果如下：
yield 后面可以有的表達(dá)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影響，當(dāng)Time.timeScale = 0f 時(shí)，yield return new WaitForSecond(x) 將不會(huì)滿足。
3. IEnumerator & Coroutine
協(xié)程其實(shí)就是一個(gè)IEnumerator（迭代器），IEnumerator 接口有兩個(gè)方法 Current 和 MoveNext() ，前面介紹的TaskManager就是利用者兩個(gè)方法對(duì)協(xié)程進(jìn)行了管理，這里在介紹一個(gè)協(xié)程的交叉調(diào)用類 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);
}
}
}
上面的代碼實(shí)現(xiàn)是兩個(gè)協(xié)程交替調(diào)用。
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