如何只在Unity编辑器启动时运行脚本？

[InitializeOnLoad]
public class MyEditorScript
{
    static MyEditorScript()
    {
        // 在这里编写只在编辑器启动时运行的代码
    }
}

using UnityEditor;

[InitializeOnLoad]
public class MyEditorScript
{
    static bool isFirstFrame = true;

    static MyEditorScript()
    {
        EditorApplication.update += OnEditorUpdate;
    }

    static void OnEditorUpdate()
    {
        if (isFirstFrame)
        {
            isFirstFrame = false;
            // 在这里编写只在编辑器启动时运行的代码
        }
    }
}

using UnityEditor;

[InitializeOnLoad]
public class MyEditorScript
{
    static MyEditorScript()
    {
        EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
    }

    static void OnPlayModeStateChanged(PlayModeStateChange state)
    {
        if (state == PlayModeStateChange.EnteredPlayMode)
        {
            // 在这里编写只在编辑器启动时运行的代码
        }
    }
}