A PropertyDrawer to show a popup field with a generic list of string for your Unity3d attribute

ExampleBehavior.cs

public class MyBehavior : MonoBehaviour {
    // This will store the string value
    [StringInList("Cat", "Dog")] public string Animal;
    // This will store the index of the array value
    [StringInList("John", "Jack", "Jim")] public int PersonID;
    
    // Showing a list of loaded scenes
    [StringInList(typeof(PropertyDrawersHelper), "AllSceneNames")] public string SceneName;
}

PropertyDrawersHelper.cs

using UnityEditor;
using UnityEngine;

public static class PropertyDrawersHelper {
  #if UNITY_EDITOR

  public static string[] AllSceneNames()
  {
    var temp = new List<string>();
    foreach (UnityEditor.EditorBuildSettingsScene S in UnityEditor.EditorBuildSettings.scenes)
    {
      if (S.enabled)
      {
        string name = S.path.Substring(S.path.LastIndexOf('/')+1);
        name = name.Substring(0,name.Length-6);
        temp.Add(name);
      }
    }
    return temp.ToArray();
  }

  #endif
}

StringInListDrawer.cs

using System;
using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
#endif

public class StringInList : PropertyAttribute {
  public delegate string[] GetStringList();

  public StringInList(params string [] list) {
    List = list;
  }

  public StringInList(Type type, string methodName) {
    var method = type.GetMethod (methodName);
    if (method != null) {
      List = method.Invoke (null, null) as string[];
    } else {
      Debug.LogError ("NO SUCH METHOD " + methodName + " FOR " + type);
    }
  }

  public string[] List {
    get;
    private set;
  }
}

#if UNITY_EDITOR
[CustomPropertyDrawer(typeof(StringInList))]
public class StringInListDrawer : PropertyDrawer {
  // Draw the property inside the given rect
  public override void OnGUI (Rect position, SerializedProperty property, GUIContent label) {
    var stringInList = attribute as StringInList;
    var list = stringInList.List;
    if (property.propertyType == SerializedPropertyType.String) {
      int index = Mathf.Max (0, Array.IndexOf (list, property.stringValue));
      index = EditorGUI.Popup (position, property.displayName, index, list);

      property.stringValue = list [index];
    } else if (property.propertyType == SerializedPropertyType.Integer) {
      property.intValue = EditorGUI.Popup (position, property.displayName, property.intValue, list);
    } else {
      base.OnGUI (position, property, label);
    }
  }
}
#endif

Thanks your code :)
Can I use your code in my commercial app?
Please let me know how I can use the code for commercial distribution.

Sure! Assume the license is MIT :)