Coroutine basics (IEnumerator) in Unity

Introduction

Coroutines let your program wait or pause without stopping everything. They help do tasks step-by-step over time.

You want to wait a few seconds before doing something, like showing a message.

You want to run a task slowly, like moving an object smoothly across the screen.

You want to load something in the background without freezing the game.

You want to repeat an action every few seconds without blocking other code.

Syntax

Unity

IEnumerator CoroutineName() {
    // code before waiting
    yield return new WaitForSeconds(seconds);
    // code after waiting
}

IEnumerator is a special return type that allows pausing and resuming the function.

yield return tells Unity when to pause and when to continue the coroutine.

Examples

This coroutine waits 2 seconds, then prints a message.

Unity

IEnumerator WaitAndPrint() {
    yield return new WaitForSeconds(2);
    Debug.Log("Hello after 2 seconds");
}

This coroutine prints a message every second forever.

Unity

IEnumerator RepeatMessage() {
    while(true) {
        Debug.Log("Repeating every 1 second");
        yield return new WaitForSeconds(1);
    }
}

Sample Program

This program starts a coroutine when the game begins. It prints a message, waits 3 seconds, then prints another message.

Unity

using UnityEngine;
using System.Collections;

public class CoroutineExample : MonoBehaviour {
    void Start() {
        StartCoroutine(WaitAndPrint());
    }

    IEnumerator WaitAndPrint() {
        Debug.Log("Start waiting...");
        yield return new WaitForSeconds(3);
        Debug.Log("3 seconds passed!");
    }
}

Important Notes

Coroutines run alongside other code without freezing the game.

You must start coroutines using StartCoroutine() in Unity.

Coroutines can pause on many things, not just time (like waiting for a condition).

Summary

Coroutines let you pause and resume code smoothly over time.

Use IEnumerator and yield return to create coroutines.

Start coroutines with StartCoroutine() to run them in Unity.