How to make an enum-like Unity inspector drop-down menu from a string array with C#?

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I'm making a Unity C# script that is meant to be used by other people as a character dialog tool to write out conversations between multiple game characters.

I have a DialogueElement class and then I create a list of DialogueElement objects. Each object represents a line of dialogue.

[System.Serializable] //needed to make ScriptableObject out of this class
public class DialogueElement
{
    public enum Characters {CharacterA, CharacterB};
    public Characters Character; //Which characters is saying the line of dialog
    public string DialogueText; //What the character is saying
}

public class Dialogue : ScriptableObject
{
    public string[] CharactersList; //defined by the user in the Unity inspector
    public List<DialogueElement> DialogueItems; //each element represents a line of dialogue
}

I want the user to be able to use the dialog tool by only interacting with the Unity inspector (so no editing code). The problem with this setup then is that the user of the dialogue tool cannot specify their own custom names (such as Felix or Wendy) for the characters in the Characters enum since they are hardcoded as "CharacterA" and "CharacterB" in the DialogueElement class.

For those not familiar with Unity, it is a game creation program. Unity lets users create physical files (known as scriptable objects) that acts as containers for class objects. The public variables of the scriptable object can be defined through a visual interface called the "inspector" as you can see below:
Unity inspector

I want to use an enum to specify which characters is the one saying the line of dialog because using an enum creates a nice drop-down menu in the inspector where the user can easily select the character without having to manually type the name of the character for each line of dialogue.

How can I allow the user to define the elements of the Characters enum? In this case I was trying to use a string array variable where the player can type the name of all the possible characters and then use that array to define the enum.

I don't know if solving the problem this way is possible. I'm open to ANY ideas that will allow the user to specify a list of names that can then be used to create a drop down menu in the inspector where the user selects one of the names as seen in the image above.

The solution doesn't need to specifically declare a new enum from a string array. I just want to find a way to make this work. One solution I thought of is to write a separate script that would edit the text of the C# script that contains the Character enum. I think this would technically work since Unity automatically recompiles scripts every time it detects they were changed and updates the scriptable objects in the inspector, but I was hoping to find a cleaner way.

Link to repository for reference:
https://github.com/guitarjorge24/DialogueTool

unity-editor unity3d enums c#
2 Answers

You can't change the enum itself as it needs to be compiled (well it is not completely impossible but I wouldn't recommend to go ways like actively change a script and force a re-compile)

Without seeing the rest of the types you need it is a bit hard but what you want you would best do in a custom editor script using EditorGUILayout.Popup. As said I don't know your exact needs and the type Characters or how exactly you reference them so for now I will assume you reference your DialogueElement to a certain character via its index in the list Dialogue.CharactersList. This basically works like an enum then!

Since these editor scripts can get quite complex I try to comment every step:

    using System;
    using System.Collections.Generic;
    using System.Linq;
#if UNITY_EDITOR
    using UnityEditor;
    using UnityEditorInternal;
#endif
    using UnityEngine;

    [CreateAssetMenu]
    public class Dialogue : ScriptableObject
    {
        public string[] CharactersList;
        public List<DialogueElement> DialogueItems;
    }

    [Serializable] //needed to make ScriptableObject out of this class
    public class DialogueElement
    {
        // You would only store an index to the according character
        // Since I don't have your Characters type for now lets reference them via the Dialogue.CharactersList
        public int CharacterID;

        //public Characters Character; 

        // By using the attribute [TextArea] this creates a nice multi-line text are field
        // You could further configure it with a min and max line size if you want: [TextArea(minLines, maxLines)]
        [TextArea] public string DialogueText;
    }

    // This needs to be either wrapped by #if UNITY_EDITOR
    // or placed in a folder called "Editor"
#if UNITY_EDITOR
    [CustomEditor(typeof(Dialogue))]
    public class DialogueEditor : Editor
    {
        // This will be the serialized clone property of Dialogue.CharacterList
        private SerializedProperty CharactersList;

        // This will be the serialized clone property of Dialogue.DialogueItems
        private SerializedProperty DialogueItems;

        // This is a little bonus from my side!
        // These Lists are extremely more powerful then the default presentation of lists!
        // you can/have to implement completely custom behavior of how to display and edit 
        // the list elements
        private ReorderableList charactersList;
        private ReorderableList dialogItemsList;

        // Reference to the actual Dialogue instance this Inspector belongs to
        private Dialogue dialogue;

        // class field for storing available options
        private GuiContent[] availableOptions;

        // Called when the Inspector is opened / ScriptableObject is selected
        private void OnEnable()
        {
            // Get the target as the type you are actually using
            dialogue = (Dialogue) target;

            // Link in serialized fields to their according SerializedProperties
            CharactersList = serializedObject.FindProperty(nameof(Dialogue.CharactersList));
            DialogueItems = serializedObject.FindProperty(nameof(Dialogue.DialogueItems));

            // Setup and configure the charactersList we will use to display the content of the CharactersList 
            // in a nicer way
            charactersList = new ReorderableList(serializedObject, CharactersList)
            {
                displayAdd = true,
                displayRemove = true,
                draggable = false, // for now disable reorder feature since we later go by index!

                // As the header we simply want to see the usual display name of the CharactersList
                drawHeaderCallback = rect => EditorGUI.LabelField(rect, CharactersList.displayName),

                // How shall elements be displayed
                drawElementCallback = (rect, index, focused, active) =>
                {
                    // get the current element's SerializedProperty
                    var element = CharactersList.GetArrayElementAtIndex(index);

                    // Get all characters as string[]
                    var availableIDs = dialogue.CharactersList;

                    // store the original GUI.color
                    var color = GUI.color;
                    // Tint the field in red for invalid values
                    // either because it is empty or a duplicate
                    if(string.IsNullOrWhiteSpace(element.stringValue) || availableIDs.Count(item => string.Equals(item, element.stringValue)) > 1)
                    {
                        GUI.color = Color.red;
                    }
                    // Draw the property which automatically will select the correct drawer -> a single line text field
                    EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width, EditorGUI.GetPropertyHeight(element)), element);

                    // reset to the default color
                    GUI.color = color;

                    // If the value is invalid draw a HelpBox to explain why it is invalid
                    if (string.IsNullOrWhiteSpace(element.stringValue))
                    {
                        rect.y += EditorGUI.GetPropertyHeight(element);
                        EditorGUI.HelpBox(new Rect(rect.x, rect.y, rect.width, EditorGUIUtility.singleLineHeight), "ID may not be empty!", MessageType.Error );
                    }else if (availableIDs.Count(item => string.Equals(item, element.stringValue)) > 1)
                    {
                        rect.y += EditorGUI.GetPropertyHeight(element);
                        EditorGUI.HelpBox(new Rect(rect.x, rect.y, rect.width, EditorGUIUtility.singleLineHeight), "Duplicate! ID has to be unique!", MessageType.Error );
                    }
                },

                // Get the correct display height of elements in the list
                // according to their values
                // in this case e.g. dependent whether a HelpBox is displayed or not
                elementHeightCallback = index =>
                {
                    var element = CharactersList.GetArrayElementAtIndex(index);
                    var availableIDs = dialogue.CharactersList;

                    var height = EditorGUI.GetPropertyHeight(element);

                    if (string.IsNullOrWhiteSpace(element.stringValue) || availableIDs.Count(item => string.Equals(item, element.stringValue)) > 1)
                    {
                        height += EditorGUIUtility.singleLineHeight;
                    }

                    return height;
                },

                // Overwrite what shall be done when an element is added via the +
                // Reset all values to the defaults for new added elements
                // By default Unity would clone the values from the last or selected element otherwise
                onAddCallback = list =>
                {
                    // This adds the new element but copies all values of the select or last element in the list
                    list.serializedProperty.arraySize++;

                    var newElement = list.serializedProperty.GetArrayElementAtIndex(list.serializedProperty.arraySize - 1);
                    newElement.stringValue = "";
                }

            };

            // Setup and configure the dialogItemsList we will use to display the content of the DialogueItems 
            // in a nicer way
            dialogItemsList = new ReorderableList(serializedObject, DialogueItems)
            {
                displayAdd = true,
                displayRemove = true,
                draggable = true, // for the dialogue items we can allow re-ordering

                // As the header we simply want to see the usual display name of the DialogueItems
                drawHeaderCallback = rect => EditorGUI.LabelField(rect, DialogueItems.displayName),

                // How shall elements be displayed
                drawElementCallback = (rect, index, focused, active) =>
                {
                    // get the current element's SerializedProperty
                    var element = DialogueItems.GetArrayElementAtIndex(index);

                    // Get the nested property fields of the DialogueElement class
                    var character = element.FindPropertyRelative(nameof(DialogueElement.CharacterID));
                    var text = element.FindPropertyRelative(nameof(DialogueElement.DialogueText));

                    var popUpHeight = EditorGUI.GetPropertyHeight(character);

                    // store the original GUI.color
                    var color = GUI.color;

                    // if the value is invalid tint the next field red
                    if(character.intValue < 0) GUI.color = Color.red;

                    // Draw the Popup so you can select from the existing character names
                    character.intValue =  EditorGUI.Popup(new Rect(rect.x, rect.y, rect.width, popUpHeight), new GUIContent(character.displayName), character.intValue,  availableOptions);

                    // reset the GUI.color
                    GUI.color = color;
                    rect.y += popUpHeight;

                    // Draw the text field
                    // since we use a PropertyField it will automatically recognize that this field is tagged [TextArea]
                    // and will choose the correct drawer accordingly
                    var textHeight = EditorGUI.GetPropertyHeight(text);
                    EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width, textHeight), text);
                },

                // Get the correct display height of elements in the list
                // according to their values
                // in this case e.g. we add an additional line as a little spacing between elements
                elementHeightCallback = index =>
                {
                    var element = DialogueItems.GetArrayElementAtIndex(index);

                    var character = element.FindPropertyRelative(nameof(DialogueElement.CharacterID));
                    var text = element.FindPropertyRelative(nameof(DialogueElement.DialogueText));

                    return EditorGUI.GetPropertyHeight(character) + EditorGUI.GetPropertyHeight(text) + EditorGUIUtility.singleLineHeight;
                },

                // Overwrite what shall be done when an element is added via the +
                // Reset all values to the defaults for new added elements
                // By default Unity would clone the values from the last or selected element otherwise
                onAddCallback = list =>
                {
                    // This adds the new element but copies all values of the select or last element in the list
                    list.serializedProperty.arraySize++;

                    var newElement = list.serializedProperty.GetArrayElementAtIndex(list.serializedProperty.arraySize - 1);
                    var character = newElement.FindPropertyRelative(nameof(DialogueElement.CharacterID));
                    var text = newElement.FindPropertyRelative(nameof(DialogueElement.DialogueText));

                    character.intValue = -1;
                    text.stringValue = "";
                }
            };

            // Get the existing character names ONCE as GuiContent[]
            // Later only update this if the charcterList was changed
            availableOptions = dialogue.CharactersList.Select(item => new GUIContent(item)).ToArray();
        }

        public override void OnInspectorGUI()
        {
            DrawScriptField();

            // load real target values into SerializedProperties
            serializedObject.Update();

            EditorGUI.BeginChangeCheck();
            charactersList.DoLayoutList();
            if(EditorGUI.EndChangeCheck())
            {
                // Write back changed values into the real target
                serializedObject.ApplyModifiedProperties();

                // Update the existing character names as GuiContent[]
                availableOptions = dialogue.CharactersList.Select(item => new GUIContent(item)).ToArray();
            }

            dialogItemsList.DoLayoutList();

            // Write back changed values into the real target
            serializedObject.ApplyModifiedProperties();
        }

        private void DrawScriptField()
        {
            EditorGUI.BeginDisabledGroup(true);
            EditorGUILayout.ObjectField("Script", MonoScript.FromScriptableObject((Dialogue)target), typeof(Dialogue), false);
            EditorGUI.EndDisabledGroup();

            EditorGUILayout.Space();
        }
    }
#endif

And this is how it would look like now

enter image description here

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