Version: 2021.3
LanguageEnglish
  • C#

MonoBehaviour.Start()

Suggest a change

Success!

Thank you for helping us improve the quality of Unity Documentation. Although we cannot accept all submissions, we do read each suggested change from our users and will make updates where applicable.

Close

Submission failed

For some reason your suggested change could not be submitted. Please <a>try again</a> in a few minutes. And thank you for taking the time to help us improve the quality of Unity Documentation.

Close

Cancel

Switch to Manual

Description

Start is called on the frame when a script is enabled just before any of the Update methods are called the first time.

Like the Awake function, Start is called exactly once in the lifetime of the script. However, Awake is called when the script object is initialised, regardless of whether or not the script is enabled. Start may not be called on the same frame as Awake if the script is not enabled at initialisation time.

The Awake function is called on all objects in the Scene before any object's Start function is called. This fact is useful in cases where object A's initialisation code needs to rely on object B's already being initialised; B's initialisation should be done in Awake, while A's should be done in Start.

Where objects are instantiated during gameplay, their Awake function is called after the Start functions of Scene objects have already completed.

The Start function can be defined as a Coroutine, which allows Start to suspend its execution (yield).

// Initializes the target variable.
// target is private and thus not editable in the Inspector

// The ExampleClass starts with Awake. The GameObject class has activeSelf // set to false. When activeSelf is set to true the Start() and Update() // functions will be called causing the ExampleClass to run. // Note that ExampleClass (Script) in the Inspector is turned off. It // needs to be ticked to make script call Start.

using UnityEngine; using System.Collections;

public class ExampleClass : MonoBehaviour { private float update;

void Awake() { Debug.Log("Awake"); update = 0.0f; }

IEnumerator Start() { Debug.Log("Start1"); yield return new WaitForSeconds(2.5f); Debug.Log("Start2"); }

void Update() { update += Time.deltaTime; if (update > 1.0f) { update = 0.0f; Debug.Log("Update"); } } }