Unity创建自定义菜单项

我尝试按照以下教程将自定义菜单项添加到主菜单栏: https://docs.unity3d.com/ScriptReference/MenuItem.html ,但我始终接收menuitem不是属性类。我确实把文件放在了名为editor的文件夹下,直接放在了assets下。

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

public class ShipFrameEditorMenu {

    [MenuItem("GameObject/Open Entity")]
    static void OpenEntity()
    {
        Debug.Log("Doing Something...");
    }
}