c# - StartCoroutine/ yield 返回模式在Unity中如何真正起作用？

我了解协程的原理。我知道如何获得标准的StartCoroutine/yield return模式以在Unity中的C#中工作，例如调用通过IEnumerator返回StartCoroutine的方法，然后在该方法中执行某项操作，执行yield return new WaitForSeconds(1);等待一秒钟，然后再执行其他操作。

我的问题是:幕后到底发生了什么？ StartCoroutine真正做什么？ IEnumerator返回什么WaitForSeconds？ StartCoroutine如何将控制权返回给被调用方法的“其他”部分？所有这些如何与Unity的并发模型(其中不使用协程同时进行很多事情)进行交互？

最佳答案

经常引用的Unity3D coroutines in detail链接已死。由于在评论和答案中提到了它，因此我将在此处发布文章的内容。该内容来自this mirror。

function LongComputation()
{
    while(someCondition)
    {
        /* Do a chunk of work */

        // Pause here and carry on next frame
        yield;
    }
}

IEnumerator LongComputation()
{
    while(someCondition)
    {
        /* Do a chunk of work */

        // Pause here and carry on next frame
        yield return null;
    }
}

IEnumerator TellMeASecret()
{
  PlayAnimation("LeanInConspiratorially");
  while(playingAnimation)
    yield return null;

  Say("I stole the cookie from the cookie jar!");
  while(speaking)
    yield return null;

  PlayAnimation("LeanOutRelieved");
  while(playingAnimation)
    yield return null;
}

IEnumerator e = TellMeASecret();
while(e.MoveNext()) { }

IEnumerator e = TellMeASecret();
while(e.MoveNext())
{
  // If they press 'Escape', skip the cutscene
  if(Input.GetKeyDown(KeyCode.Escape)) { break; }
}

List<IEnumerator> unblockedCoroutines;
List<IEnumerator> shouldRunNextFrame;
List<IEnumerator> shouldRunAtEndOfFrame;
SortedList<float, IEnumerator> shouldRunAfterTimes;

foreach(IEnumerator coroutine in unblockedCoroutines)
{
    if(!coroutine.MoveNext())
        // This coroutine has finished
        continue;

    if(!coroutine.Current is YieldInstruction)
    {
        // This coroutine yielded null, or some other value we don't understand; run it next frame.
        shouldRunNextFrame.Add(coroutine);
        continue;
    }

    if(coroutine.Current is WaitForSeconds)
    {
        WaitForSeconds wait = (WaitForSeconds)coroutine.Current;
        shouldRunAfterTimes.Add(Time.time + wait.duration, coroutine);
    }
    else if(coroutine.Current is WaitForEndOfFrame)
    {
        shouldRunAtEndOfFrame.Add(coroutine);
    }
    else /* similar stuff for other YieldInstruction subtypes */
}

unblockedCoroutines = shouldRunNextFrame;

YieldInstruction y;

if(something)
 y = null;
else if(somethingElse)
 y = new WaitForEndOfFrame();
else
 y = new WaitForSeconds(1.0f);

yield return y;

IEnumerator DoSomething()
{
  /* ... */
}

IEnumerator DoSomethingUnlessInterrupted()
{
  IEnumerator e = DoSomething();
  bool interrupted = false;
  while(!interrupted)
  {
    e.MoveNext();
    yield return e.Current;
    interrupted = HasBeenInterrupted();
  }
}

IEnumerator UntilTrueCoroutine(Func fn)
{
   while(!fn()) yield return null;
}

Coroutine UntilTrue(Func fn)
{
  return StartCoroutine(UntilTrueCoroutine(fn));
}

IEnumerator SomeTask()
{
  /* ... */
  yield return UntilTrue(() => _lives < 3);
  /* ... */
}