Unity协程（Coroutine）之yield和迭代原理分析

public static IEnumerable<int> GenerateFibonacci()
｛
    yield return 0;
    yield return 1;
    int last0 = 0, last1 = 1, current;
    while (true)
    ｛
        current = last0 + last1;
        yield return current;
        last0 = last1;
        last1 = current;
    ｝
｝

1. 游戏结算分数时，分数从0逐渐上涨，而不是直接显示最终分数
2. 人物对话时，文字一个一个很快的出现，而不是一下突然出现
3. 10、9、8……0的倒计时
4. 某些游戏（如拳皇）掉血时血条UI逐渐减少，而不是突然降低到当前血量

using UnityEngine;
using System.Collections;
public class dialog_yield : MonoBehaviour ｛
    public string dialogStr = "yield return的作用是在执行到这行代码之后，将控制权立即交还给外部。yield return之后的代码会在外部代码再次调用MoveNext时才会执行，直到下一个yield return——或是迭代结束。虽然上面的代码看似有个死循环，但事实上在循环内部我们始终会把控制权交还给外部，这就由外部来决定何时中止这次迭代。有了yield之后，我们便可以利用“死循环”，我们可以写出含义明确的“无限的”斐波那契数列。";
    public float speed = 5.0f;
    void Start ()
｛
        StartCoroutine(ShowDialog());
 ｝
    void Update ()
｛
 ｝  
    IEnumerator ShowDialog()
｛
        float timeSum = 0.0f;
        while(guiText.text.Length < dialogStr.Length)｛
            timeSum += speed * Time.deltaTime;
            guiText.text = dialogStr.Substring(0,         System.Convert.ToInt32(timeSum));
            yield return null;
        ｝
    ｝
｝

1. null - the coroutine executes the next time that it is eligible
2. WaitForEndOfFrame - the coroutine executes on the frame, after all of the rendering and GUI is complete
3. WaitForFixedUpdate - causes this coroutine to execute at the next physics step, after all physics is calculated
4. WaitForSeconds - causes the coroutine not to execute for a given game time period
5. WWW - waits for a web request to complete (resumes as if WaitForSeconds or null)
6. Another coroutine - in which case the new coroutine will run to completion before the yielder is resumed

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;
        ｝
｝
    IEnumerator UpdateCoutine()
    ｛
        Debug.Log("This is Update Coroutine Call Before");
        yield return new WaitForSeconds(1f);
        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 new WaitForSeconds(1f);
        Debug.Log("This is Late Coroutine Call After");
    ｝
｝

1. null - the coroutine executes the next time that it is eligible
2. WaitForEndOfFrame - the coroutine executes on the frame, after all of the rendering and GUI is complete
3. WaitForFixedUpdate - causes this coroutine to execute at the next physics step, after all physics is calculated
4. WaitForSeconds - causes the coroutine not to execute for a given game time period
5. WWW - waits for a web request to complete (resumes as if WaitForSeconds or null)
6. Another coroutine - in which case the new coroutine will run to completion before the yielder is resumed

using System;  
using System.Collections.Generic;  
using System.Linq;  
using UnityEngine;  
using System.Collections;  
[RequireComponent(typeof(GUIText))]  
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  
        guiText.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);  
        ｝  
    ｝  
｝