Retrieving array size but no array was provided

[tribaleur]

Hello,

I’m trying to do a custom PropertyDrawer for a custom class with a List. To format the list i use the ReordorableList classe provided by Unity.

The problème is when i try to initialise the list, i got the error : Retrieving array size but no array was provided.

Here my PropertyDrawer :

using UnityEngine;
using UnityEditor;
using UnityEditorInternal;

[CustomPropertyDrawer(typeof(SpellsEffectsList))]
public  class Drawer_SpellsEffectsList : PropertyDrawer {
    //_____ PROTECTED PROPERTIES ________________________________________________
    protected ReorderableList _reorderableList;
    protected SerializedProperty _serializedList;
    protected string _headerText = "";



    //_____ CONSTRUCTOR _________________________________________________________
    ~Drawer_SpellsEffectsList () {       
        // Delete Callback to make sure we don't get memory leaks etc.
        this._reorderableList.drawHeaderCallback -= this.DrawHeader;
        this._reorderableList.drawElementCallback -= this.DrawElement;

        this._reorderableList.onAddCallback -= this.AddItem;
        this._reorderableList.onRemoveCallback -= this.RemoveItem;
    }





    //_____ TRIGGER _____________________________________________________________
    public override void OnGUI (Rect position, SerializedProperty property, GUIContent label){
        this._reorderableList = new ReorderableList(property.serializedObject, property, true, true, true, true);
            // => this is where the error occured : Input elements should be an Array SerializedProperty
       
        // Add listeners to draw events
        this._reorderableList.drawHeaderCallback += this.DrawHeader;
        this._reorderableList.drawElementCallback += this.DrawElement;

        this._reorderableList.onAddCallback += this.AddItem;
        this._reorderableList.onRemoveCallback += this.RemoveItem;

        // Add header
        this._headerText = label.text;

        // Override logic works on the entire property
        EditorGUI.BeginProperty(position, label, property);
       
        this._reorderableList.DoLayoutList();

        EditorGUI.EndProperty();
       
        // Apply changes to the serializedProperty
        property.serializedObject.ApplyModifiedProperties();
    }



    //_____ METHODES ____________________________________________________________   
    /* -------------------------------------------------------------------------------------------------------------------------
     * Draws one element of the list
     * ------------------------------------------------------------------------------------------------------------------------- */
    protected void  DrawElement (Rect rect, int index, bool active, bool focused) {
        SerializedProperty item = this._serializedList.GetArrayElementAtIndex(index);
        SerializedProperty element_Id = item.FindPropertyRelative("_id");

        EditorGUI.BeginChangeCheck();
        EditorGUI.PropertyField(rect, element_Id);
        if (EditorGUI.EndChangeCheck()){
            // Set the item as modified and add the modification in the undo action list
            Undo.RecordObject(this._serializedList.serializedObject.targetObject, "Cancel item's modification on " + this._serializedList.GetType().ToString() + " reorderable list");
        }   
    }
   
   
    /* -------------------------------------------------------------------------------------------------------------------------
     * Draws the header of the list
     * ------------------------------------------------------------------------------------------------------------------------- */
    private void DrawHeader(Rect rect){
        GUI.Label(rect, this._headerText);
    }
         
    /* -------------------------------------------------------------------------------------------------------------------------
     * Add an item in the list
     * ------------------------------------------------------------------------------------------------------------------------- */
     private void AddItem(ReorderableList list){
        this._serializedList.InsertArrayElementAtIndex(list.index);

        // Set the list as modified and add the modification in the undo action list
        Undo.RecordObject(this._serializedList.serializedObject.targetObject, "Cancel Add item on " + this._serializedList.GetType().ToString() + " reorderable list");
     }

    /* -------------------------------------------------------------------------------------------------------------------------
     * Delete an item of the list
     * ------------------------------------------------------------------------------------------------------------------------- */
     private void RemoveItem(ReorderableList list) {
        this._serializedList.DeleteArrayElementAtIndex(list.index);
       
        // Set the list as modified and add the modification in the undo action list
        Undo.RecordObject(this._serializedList.serializedObject.targetObject, "Cancel Remove item on " + this._serializedList.GetType().ToString() + " reorderable list");
     }
}

Here my SpellsEffectsList :

using System.Collections.Generic;
using System;

[Serializable]
public class SpellsEffectsList : List<SpellEffect> {
    // Only some methodes here ...
}

Here how the list is declared :

[SerializeField]
    private SpellsEffectsList    _spellsEffects    = new SpellsEffectsList();

Here how the the propertyDrawer is called from a custom Editor :

public override void OnInspectorGUI () {
        // few code ...
        EditorGUILayout.PropertyField(serializedSpell.FindProperty("_spellsEffects"), true);
        // some other code ...
    }

When i’m in debug mode,I have this in Visual Studio :

I don’t understand why i have this problème.

Do you have an idea ?

Thanks for your help.

[eses]

Hi @tribaleur

Is there a specific reason you are extending generic list?

public class SpellsEffectsList : List<SpellEffect> {}

Try using list with type instead, and you should get your list working (in Custom Editor):

public List<SpellEffect> list = new List<SpellEffect>();

[tribaleur]

Hi Eses,

I already tried it, but i have the message “nullReferenceException: Object reference not set to an instance of an object” in the Editor when i call the propertyDrawer .

In the custom Editor :

public override void OnInspectorGUI () {

        Spell gameObject_Spell = (Spell)target;
        if (gameObject_Spell.SpellsEffects == null) { Debug.Log("Null liste"); }
        else { Debug.Log("Not Null liste"); } // The log show me this message so the list is instanciate  ?
        SerializedObject serializedSpell = new SerializedObject(gameObject_Spell);

*** EDIT ***
SerializedProperty spl = serializedSpell.FindProperty("_spellsEffects");
// This always return Null even if the serializedSpell have the property "_spellsEffects" set.
// I tried as well with the name of the Get accessor but it still doesn't works.
// So the question is why the List can't be found by "FindProperty()" ?
*** END EDIT ***

        // ...

        EditorGUILayout.PropertyField(serializedSpell.FindProperty("_spellsEffects"), true);
        // => The error message is there !

        // ...
    }

I don’t understand why i have this error.

About the extend of the generic list : it’s to modify the Add() method and to create some news one

[eses]

What I mean;

I tried this - if using just a generic list, this will find the list:

var prop = serializedObject.FindProperty("list");

And the classes look like this:

public class SpellEffects : MonoBehaviour
{
    // this will work
    public List<SpellEffect> list = new List<SpellEffect>();
}

[System.Serializable]
public class SpellEffect
{
    public string someString = "foo";
}

But if using sub class of generic list (what you were using) Unity serialized property doesn’t seem to be able to find the list… Maybe such list isn’t supported.

[Errorsatz]

You can achieve similar results by using extension methods. For example:

public static class SpellEffectListExtensions
{
   public void AddEffect(this IList<SpellEffect> self, SpellEffect item)
   {
      self.Add(item);
      // Whatever else
   }
}

...

List<SpellEffect> list;
list.AddEffect(myEffect);

[tribaleur]

Hi guys,

Thanks for your help.

@eses : I tried the following to understand.

I declared 3 list :

[SerializeField]
    private SpellsEffectsList    _spellsEffects    = new SpellsEffectsList();
    [SerializeField]
    private List<SpellEffect>    _spellsEffects2    = new List<SpellEffect>();
    [SerializeField]
    private List<Object>    _objects    = new List<Object>();

In the editor i tried this :

        SerializedProperty se = serializedObject.FindProperty("_spellsEffects"); // Return a serialisedProperty but not as an array
        SerializedProperty se2 = serializedObject.FindProperty("_spellsEffects2"); // Return Null
        SerializedProperty lo = serializedObject.FindProperty("_objects"); // Return an empty List of object (isArray = true)

So it doesn’t works when the elements have the SpellEffect type.
After few test i found why … SpellEffect is an abstract class for inheritance. It’s looks like unity can’t serialise abstract class. I have to think on how to change that classe to not abstract.

Anyway, SpellsEffectsList is still not recognised as an array when List does. So i have to think on @ErrorStatz solution. Thanks for your help guys.