Coroutines in Unity3d (C# version)

Coroutines in C# work the same way that they do in Javascript (UnityScript), the only difference is that they require more typing (they have a slightly more complicated syntax). You should see the blog post on Javascript coroutines first.

Here, I present the differences:

Coroutines must have the IEnumerator return type:

IEnumerator MyCoroutine()
{
	//This is a coroutine
}

To invoke a coroutine you must do it using the StartCoroutine method:

public class MyScript : MonoBehaviour 
{
    void Start()
    {
		StartCoroutine(MyCoroutine());
    }

    IEnumerator MyCoroutine()
    {
        //This is a coroutine
    }
}

The yield statement becomes yield return in C# :

IEnumerator MyCoroutine()
{
    DoSomething();
    yield return 0;	//Wait one frame, the 0 here is only because we need to return an IEnumerable
    DoSomethingElse();
}

Remember that we need to return an IEnumerable, so the Javascript yield; becomes yield return 0; in C#

Also, since C# requires you to use the new operator to create objects, if you want to use WaitForSeconds you have to use it like this:

IEnumerator MyCoroutine()
{
    DoSomething();
    yield return new WaitForSeconds(2.0f);	//Wait 2 seconds
    DoSomethingElse();
}

Happy coroutining

Pingback: Coroutines in Unity3d (Javascript version) - Silent Kraken
http://www.facebook.com/gtjuggler Alex Schwartz

Thanks Seth for sharing these basics. Definitely useful to those looking to learn.

One note: I had heard that returning null is ever so slightly faster than returning 0 when yielding in a coroutine due to the allocation for creating a new variable
http://cjcurrie.net/ cjcurrie

So how do you create a coroutine that returns a value at the end?
http://rockingtech.blogspot.com Robert

thanks for sharing the code for this. i really needed to know and i will use a slightly modified one in my application. What if i wanted to return more than one values. Is there any way i can do it.
Richard Hensman

Hi,

So according to Unity Docs, you can’t use yield in an Update statement, but you can start a CoRoutine that does.

I am somewhat confused by this. In my code I have two objects. Object 1 needs to make two calls to Object 2. Object 2, in each case, starts an animation, waits X seconds (local member of Object 2), then returns to Object 1. So I think Object 2 code looks like:

IEnumerator MethodTwo() {
AnimationClip.play();
yield return new WaitForSeconds(x);
}

But does Object 1 need to “yield” at all, or can it just call MethodTwo(); directly?

Thanks,
Rich
http://www.silentkraken.com/ Daniel Rodriguez

If you want Object1 to wait for Object 2 it needs to yield StartCoroutine on Object2.
Chandan

Thanks for the post
http://twitter.com/m_s_ramzy Mina Samy

Hi, thanks for explaining
I have a question: why use a coroutine instead of a regular method ?
thanks
Dusan Petrovcic

ok explain why this doesn’t work please

[Code]
using UnityEngine;
using System.Collections;

public class CraftPosition : MonoBehaviour {
    public bool Building = true ;
    public bool Builded = false ;
    public float smooth = 1 ;
    public float Distance = 3 ;
    GameObject Player ;
    public Create Script ;

    public float time ;
    public float time1 ;
    public Vector3 position ;
    void Start () {
        Player = GameObject.Find(“Camera”);
        Script = Player.GetComponent(“Create”) as Create;
    }

    IEnumerator Wait3Sec (){
        yield return new WaitForSeconds(3.0f);
    }

    void Update () {

        //snap in to player’s controll
        if (Building){
            Player = GameObject.Find(“Camera”);
            transform.position = Vector3.Lerp (transform.position , Player.transform.position + Player.transform.forward * Distance , Time.deltaTime * smooth);
        }

        // change craft object to gravity and snap out of player’s controll
        if (Building){
            if (Input.GetKeyDown(KeyCode.Mouse0)){
                transform.rigidbody.useGravity = true ;
                Building = false ;
                Builded = true ;

            }
        }
        // after 3 sec make object to kinematic so it’s builded object
        if (Builded == true){
            position = transform.position;
            time = Time.time;
            //while (position == transform.position || time1 – time < 3) {
            StartCoroutine(Wait3Sec());
            //time1 = Time.time;
            transform.rigidbody.isKinematic = true;
            //}
            Script.NotBuilding = true;
            Builded = false ;
        }
    }
}

[/Code]