Sometimes it can be useful to make parts of your Edit mode project code run immediately when the Unity Editor launches without requiring any user action. You can do this by applying the InitializeOnLoad attribute to a class which has a static constructor. A static constructor is a function with the same name as the class, declared static and without a return type or parameters. For more information, refer to Static constructors in the Microsoft C# documentation.
using UnityEngine;
using UnityEditor;
[InitializeOnLoad]
public class Startup {
static Startup()
{
Debug.Log("Up and running");
}
}
A static constructor is always guaranteed to be called before any static function or instance of the class is used, but the InitializeOnLoad attribute ensures it’s called when the Editor launches. Static constructors with this attribute are called when scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary in the project are recompiled, also known as a domain reload. This happens when:
An example use of the initialize on load functionality is setting up a regular callback which could be thought of as a sort of “frame update” for the Editor application. The EditorApplication class has a delegate called update which is called many times per second while the Editor is running. The following code example defines a small custom class decorated with [InitializeOnLoad] and assigns a member method to the EditorApplication.update delegate so that it runs and begins printing Updating to the console on Editor launch:
using UnityEditor;
using UnityEngine;
// InitializeOnLoad ensures this code runs on Editor launch
[InitializeOnLoad]
class MyClass
{
// Define a static constructor in which we assign the custom Update method to the delegate
static MyClass ()
{
EditorApplication.update += Update;
}
// Define a method with the required signature that performs work we want to do on launch
static void Update ()
{
Debug.Log("Updating");
}
}