Unity script life cycle and execution sequence

Catalog

• Script life cycle
  • MonoBehavior Life cycle diagram
• Script execution order
  • Custom execution order

@( List of articles )

stay Unity in , A script can be understood as an instruction code attached to a game object to define the behavior of the game object . You must bind to a GameObject to start its lifecycle . Game objects can be understood as containers that can hold various components , All the components of the game object together determine the behavior of the object and the performance in the game .

Script life cycle

Unity Common inevitable events in scripts are shown in the following table

name	trigger	purpose
Awake	Called when a script instance is created	Used for initialization of game objects , Be careful Awake The execution of is earlier than that of all scripts Start function
OnEnable	Called when an object becomes available or active	purpose
Start	Update The function is called before the first run	Used for initialization of game objects
Update	Once per frame	Used to update game scenes and status
FixedUpdate	Called once per fixed physical interval	Used to update the physical state
LateUpdate	Once per frame （ stay update Then call ）	Used to update game scenes and status , Camera related updates are usually placed here
OnGUI	Rendering and processing OnGUI event	purpose
OnDisable	Called when the current object is unavailable or inactive	purpose
OnDestroy	Called when the current object is destroyed	purpose

Let's take a look at the call timing of these inevitable events with code
Create a new one C# Script , And add the following code , Then hang it on any GameObject

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

public class TestTest : MonoBehaviour
{
    private void Awake()
    {
        Debug.Log("Awake");
    }

    private void OnEnable()
    {
        Debug.Log("OnEnable");
    }

    // Start is called before the first frame update
    void Start()
    {
        Debug.Log("Start");
    }

    // Update is called once per frame
    void Update()
    {
        Debug.Log("Update");
    }

    private void FixedUpdate()
    {
        Debug.Log("FixedUpdate");
    }

    private void LateUpdate()
    {
        Debug.Log("LateUpdate");
    }

    private void OnGUI()
    {
        Debug.Log("OnGUI");
    }

    private void OnDisable()
    {
        Debug.Log("OnDisable");
    }

    private void OnDestroy()
    {
        Debug.Log("OnDestroy");
    }
}

The print result is shown in the following figure ：

You can find ,Awake, Start Functions are called once when the game object is created .
When you adjust the script's visible state during the game , Will call... Separately OnEnable, OnDisable function , and Awake and Start Will no longer call , That is, once the script is mounted ,Awake and Start There is and will only be executed once .
and Update, FixedUpdate, LateUpdate, OnGUI Function will be called many times during the game （ The number on the right side of the log window indicates the number of times the log information is printed ）.
Finally, when the game object is destroyed , Will call in turn OnDisable, OnDestory function .

MonoBehavior Life cycle diagram

Here is a life cycle diagram drawn by a foreign friend

Script execution order

In game development , Inevitably, many scripts will be used , So how to determine the sequence of calls between different scripts

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

public class Test1 : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        Debug.Log("start 1");
    }

    private void Awake()
    {
        Debug.Log("awake 1");
    }

    // Update is called once per frame
    void Update()
    {
        Debug.Log("update 1");
    }
}

Add the above code to Test1, Test2 and Test3 Script （ Modify the printed log properly ）, And mount to different game objects .
The order of mounting is to mount first Test3, Re mount Test2, Finally mount Test1
The printing result is shown in the figure below

Print the result first Test1 Of , Re print Test2, Finally print Test3.
In fact, the execution order of the script is related to the sequence of attaching to the game object . The last execution that is mounted first , The last mounted is executed first （ If the reader has doubts , You can constantly adjust the mounting order of scripts , See whether the log printing is consistent with the above conclusion ）.

It should be noted that , Regardless of the order in which multiple scripts are executed , But all the scripts Awake Functions must be better than all Start The function is executed first , be-all Start Functions must be better than all Update The function is executed first , Other ordered lifecycle functions are similar （ It can also be seen from the log information in the above figure ）.

Custom execution order

Sometimes there may be such a need ,A Attribute instantiation in scripts may require B Properties in the script , So in A When the script attribute is instantiated , Must ensure B The script has been instantiated . Of course, we can do it by hanging it on A Script remount B Script to achieve . But in real development , Many scripts are used , It's hard to remember the order in which each script is mounted . therefore Unity Provides Script Execution Order Configuration item , To configure the execution order of multiple scripts .
Select a script file by clicking it in the project panel , The script details will appear in the property panel , Choose... In the upper right corner Execution Order..., Open the interface shown in the following figure

Click on “+” You can add scripts , Set it up order value ,order The smaller the value is, the earlier it is executed ,order The higher the value, the later the execution