如何确保一个协程在另一个协程运行之前完成？答案

【问题标题】：How to ensure that one coroutine completes before another is run?如何确保一个协程在另一个协程运行之前完成？
【发布时间】：2018-03-10 14:07:19
【问题描述】：

我有两个协程。一个有几个协程。在第二个协程在Start() 方法内运行之前，第一个协程不会等待第二个协程完成。请看下面的代码。

void Start() {
    StartCoroutine(DrawLineWithDuration (3.0f));
    StartCoroutine (changeLinePos (2.0f));
}

IEnumerator DrawLineWithDuration (float duration)  {

    lr.positionCount = 1;
    lr.SetPosition(0, GetPoint(0));

    float waitDur = duration / numPoints;

    for (int i = 1; i < numPoints + 1; i++) {
        float t = i / (float)numPoints;
        lr.positionCount = i+1;
        lr.SetPosition(i, GetPoint(t));

        yield return new WaitForSeconds(waitDur);
    }
}

IEnumerator moveToPosition1(Vector3 toPosition, float duration)
{

    float counter = 0;

    Vector3 startPos = points[1];

    while (counter < duration)
    {
        counter += Time.deltaTime;
        points[1] = Vector3.Lerp(startPos, toPosition, counter / duration);
        yield return null;
    }

}

IEnumerator moveToPosition2(Vector3 toPosition, float duration)
{
    float counter = 0;
    Vector3 startPos = points[2];

    while (counter < duration)
    {
        counter += Time.deltaTime;
        points[2] = Vector3.Lerp(startPos, toPosition, counter / duration);
        yield return null;
    }
}


IEnumerator moveToOriginal1(Vector3 toPosition, float duration)
{

    float counter = 0;

    Vector3 startPos = points[1];

    while (counter < duration)
    {
        counter += Time.deltaTime;
        points[1] = Vector3.Lerp(startPos, toPosition, counter / duration);
        yield return null;
    }

}

IEnumerator moveToOriginal2(Vector3 toPosition, float duration)
{
    float counter = 0;
    Vector3 startPos = points[2];

    while (counter < duration)
    {
        counter += Time.deltaTime;
        points[2] = Vector3.Lerp(startPos, toPosition, counter / duration);
        yield return null;
    }
}


IEnumerator changeLinePos(float waitTime)   {

    yield return new WaitForSeconds(waitTime);

    while (isRepeating) {
        StartCoroutine (moveToPosition1 (newPos1, moveDuration));
        StartCoroutine (moveToPosition2 (newPos2, moveDuration));
        yield return new WaitForSeconds (betweenPosMoveDelay);

        StartCoroutine (moveToOriginal1 (oriPos1, moveDuration));
        StartCoroutine (moveToOriginal2 (oriPos2, moveDuration));

        yield return new WaitForSeconds (betweenPosMoveDelay);
    }

}

在Start() 内，我如何确保StartCoroutine(DrawLineWithDuration (3.0f)); 在StartCoroutine (changeLinePos (2.0f)); 开始之前完成其给定的持续时间。同样在changeLinePos(float waitTime) 中，我如何确保moveToPosition1 和moveToPosition2 在moveToOriginal1 和moveToOriginal1 和moveToOriginal2 之前完成？

【问题讨论】：

标签： unity3d coroutine

【解决方案1】：

其实很简单，可以yield return StartCoroutine(DrawLineWithDuration (3.0f));作为changeLinePos的第一行，像这样：

void Start() {    
    StartCoroutine (ChangeLinePos (2.0f));
}

IEnumerator ChangeLinePos(float waitTime)   {
    yield return StartCoroutine(DrawLineWithDuration (3.0f));
    while (isRepeating) {
        StartCoroutine (MoveToOriginal1 (oriPos1, moveDuration));
        StartCoroutine (MoveToOriginal2 (oriPos2, moveDuration));
        yield return new WaitForSeconds (betweenPosMoveDelay);
    }
}

IEnumerator MoveToOriginal1(Vector3 toPosition, float duration) {
    yield return StartCoroutine (MoveToPosition1 (newPos1, moveDuration));
    //Rest of MoveToOriginal1 code
}

IEnumerator MoveToOriginal2(Vector3 toPosition, float duration) {
    yield return StartCoroutine (MoveToPosition2 (newPos2, moveDuration));
    //Rest of MoveToOriginal1 code
}

有了这个结构，时序如下：

ChangeLinePos 开始于 Start()
第一行以DrawLineWithDuration 开始并停止ChangeLinePos 的执行，直到前者完成
当DrawLineWithDuration完成时，如果isRepeating==true，代码同步启动MoveToOriginal1和MoveToOriginal2
MoveToOriginal1 和 MoveToOriginal2 都启动 MoveToPosition1 和 MoveToPosition2 并等待最后两个完成。

我离开了while，因为它似乎受到协程之外的东西的影响，所以请确保isRepeating在需要时更改为false，否则MoveToOriginal1和MoveToOriginal2协程将被启动一直到应用程序停止为止。

【讨论】：