Custom Attribute : an Array Size Limiter

Hi everybody.

I'm trying to make a Custom Attribute to set a max size for array properties. But I have some difficulties with the SerializedProperty class' accessors...

Here's my code :

Code (CSharp):

1. using UnityEngine;
2.  
3. #if UNITY_EDITOR
4. using UnityEditor;
5. #endif
6.  
7. public class ArrayLimitAttribute : PropertyAttribute
8. {
9.  
10.     #region Members
11.  
12.         private    uint    m_Size    = 0;
13.  
14.     #endregion
15.  
16.  
17.     #region Initialisation / Destruction
18.  
19.         private ArrayLimitAttribute()
20.         {
21.  
22.         }
23.  
24.         public ArrayLimitAttribute(int _MaxArraySize)
25.         {
26.             m_Size = (_MaxArraySize < 0) ? 0 : (uint)_MaxArraySize;
27.         }
28.  
29.         public ArrayLimitAttribute(uint _MaxArraySize)
30.         {
31.             m_Size = _MaxArraySize;
32.         }
33.  
34.     #endregion
35.  
36.  
37.     #region Accessors
38.  
39.         public int MaxSize
40.         {
41.             get { return (int)m_Size; }
42.         }
43.  
44.     #endregion
45.  
46. }
47.  
48. #if UNITY_EDITOR
49.  
50. [CustomPropertyDrawer(typeof(ArrayLimitAttribute))]
51. public class ArrayLimitDrawer : PropertyDrawer
52. {
53.  
54.     #region UI
55.  
56.         public override void OnGUI(Rect _Position, SerializedProperty _Property, GUIContent _Label)
57.         {
58.             ArrayLimitAttribute limit    = attribute as ArrayLimitAttribute;
59.             int                    maxSize = limit.MaxSize;
60.  
61.             if(_Property.isArray)
62.             {
63.                 if(_Property.arraySize > maxSize)
64.                 {
65.                     _Property.arraySize = maxSize;
66.                 }
67.             }
68.  
69.             else
70.             {
71.                 Debug.Log("The ArrayLimitAttribute is useless for properties that are not an array.");
72.             }
73.  
74.             EditorGUI.PropertyField(_Position, _Property);
75.         }
76.  
77.     #endregion
78.  
79. }
80.  
81. #endif

When I use this attribute for an int array, _Property.isArray returns false. For a string array, isArray returns true. Why ? Note that when isArray is true, _Property.arraySize value is always 0.

Results are the same if you use Lists.

So, two questions : why the values are not the expected ones ? And How I can do my Array Size Limiter with fake values from SerializedProperty ?

Thanks for your answers.

 

The property drawer is executed once per item in the array, and not for the entire array as a single property..
You can verify that by debugging and checking what is the SerializedProperty you're currently drawing.

 

Ok you're right, it's clearly that. So, does it means there's no way to do what I want on the array ?

Of course, I can do it by creating a CustomEditor for my class... But I prefer create one attribute, to avoid create tons of Custom Editor for every class that could use it !

 

I don't think you could do that with the current support from Property drawers...

You *could* get away with some hacked solution by defining a new wrapper type around your array. This will be a new class (or struct) that will internally hold your actual array. You could decorate this type with your attribute (getting the 1 to 1 mapping between the attribute and the property it's used on), internally you would check whether the property satisfies your condition (e.g: whether the internal array is sized within limits).

EDIT: i just googled this and found this solution (which is pretty much what i just wrote, but takes it one step further using implicit conversions: http://answers.unity3d.com/questions/605875/custompropertydrawer-for-array-types-in-43.html)

 

Ok. I found this one, but the post was on version 4.3 so I hoped that's possible now. :/

Thanks for your answers ^^