MonoBehaviour.StartCoroutine

Description

Starts a coroutine.

The execution of a coroutine can be paused at any point using the yield statement. The yield return value specifies when the coroutine is resumed. Coroutines are excellent when modelling behaviour over several frames. Coroutines have virtually no performance overhead. StartCoroutine function always returns immediately, however you can yield the result. This will wait until the coroutine has finished execution. There is no guarantee that coroutines end in the same order that they were started, even if they finish in the same frame.

When using JavaScript it is not necessary to use StartCoroutine, the compiler will do this for you. When writing C# code you must call StartCoroutine.

// In this example we show how to invoke a coroutine and continue executing
// the function in parallel.

function Start() {
    // - After 0 seconds, prints "Starting 0.0"
    // - After 0 seconds, prints "Before WaitAndPrint Finishes 0.0"
    // - After 2 seconds, prints "WaitAndPrint 2.0"
    print ("Starting " + Time.time);
    // Start function WaitAndPrint as a coroutine. And continue execution while it is running

    // this is the same as WaitAndPrint(2.0) as the compiler does it for you automatically
    StartCoroutine(WaitAndPrint(2.0));
    print ("Before WaitAndPrint Finishes " + Time.time);
}

function WaitAndPrint (waitTime : float) {
    // suspend execution for waitTime seconds
    yield WaitForSeconds (waitTime);
    print ("WaitAndPrint "+ Time.time);
}

using UnityEngine;
using System.Collections;

// In this example we show how to invoke a coroutine and continue executing
// the function in parallel.

public class ExampleClass : MonoBehaviour
{
    // In this example we show how to invoke a coroutine and
    // continue executing the function in parallel.

    private IEnumerator coroutine;

    void Start()
    {
        // - After 0 seconds, prints "Starting 0.0"
        // - After 0 seconds, prints "Before WaitAndPrint Finishes 0.0"
        // - After 2 seconds, prints "WaitAndPrint 2.0"
        print("Starting " + Time.time);

        // Start function WaitAndPrint as a coroutine.

        coroutine = WaitAndPrint(2.0f);
        StartCoroutine(coroutine);

        print("Before WaitAndPrint Finishes " + Time.time);
    }

    // every 2 seconds perform the print()
    private IEnumerator WaitAndPrint(float waitTime)
    {
        while (true)
        {
            yield return new WaitForSeconds(waitTime);
            print("WaitAndPrint " + Time.time);
        }
    }
}

Another example:

// In this example we show how to invoke a coroutine and wait until it
// is completed

function Start() {
    // - After 0 seconds, prints "Starting 0.0"
    // - After 2 seconds, prints "WaitAndPrint 2.0"
    // - After 2 seconds, prints "Done 2.0"
    print ("Starting " + Time.time);
    // Start function WaitAndPrint as a coroutine. And wait until it is completed.
    // the same as yield WaitAndPrint(2.0);
    yield StartCoroutine(WaitAndPrint(2.0));
    print ("Done " + Time.time);
}

function WaitAndPrint (waitTime : float) {
    // suspend execution for waitTime seconds
    yield WaitForSeconds (waitTime);
    print ("WaitAndPrint "+ Time.time);
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    IEnumerator Start() {
        print("Starting " + Time.time);
        yield return StartCoroutine(WaitAndPrint(2.0F));
        print("Done " + Time.time);
    }
    IEnumerator WaitAndPrint(float waitTime) {
        yield return new WaitForSeconds(waitTime);
        print("WaitAndPrint " + Time.time);
    }
}

Description

Starts a coroutine named methodName.

In most cases you want to use the StartCoroutine variation above. However StartCoroutine using a string method name allows you to use StopCoroutine with a specific method name. The downside is that the string version has a higher runtime overhead to start the coroutine and you can pass only one parameter.

// In this example we show how to invoke a coroutine using a string name and stop it

function Start () {
    StartCoroutine("DoSomething", 2.0);
    yield WaitForSeconds(1);
    StopCoroutine("DoSomething");
}

function DoSomething (someParameter : float) {
    while (true) {
        print("DoSomething Loop");
        // Yield execution of this coroutine and return to the main loop until next frame
        yield;
    }
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    IEnumerator Start() {
        StartCoroutine("DoSomething", 2.0F);
        yield return new WaitForSeconds(1);
        StopCoroutine("DoSomething");
    }
    IEnumerator DoSomething(float someParameter) {
        while (true) {
            print("DoSomething Loop");
            yield return null;
        }
    }
}

Parameters

Description

Starts a Coroutine named coroutine.

Create a Coroutine. Any coroutine name can be used. A StartCoroutine function terminates immediately, however, the Coroutine it creates runs as expected. A created coroutine can start another coroutine. These two coroutines can operate together in many ways. This includes both coroutine running in parallel. Alternatively one coroutine can stop the other while it continues itself. The script example below shows one coroutine pausing at it starts another one. Once this second coroutine finishes it restarts the first one.

no example available in JavaScript

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ExampleClass : MonoBehaviour
{
    void Start()
    {
        StartCoroutine(coroutineA());
    }

    IEnumerator coroutineA()
    {
        // wait for 1 second
        Debug.Log("coroutineA created");
        yield return new WaitForSeconds(1.0f);
        yield return StartCoroutine(coroutineB());
        Debug.Log("coroutineA running again");
    }

    IEnumerator coroutineB()
    {
        Debug.Log("coroutineB created");
        yield return new WaitForSeconds(2.5f);
        Debug.Log("coroutineB enables coroutineA to run");
    }
}