Question Script can't find my CustomAttribute namespace

I've this script

Code (csharp):

1. using UnityEngine;
2.  
3.     public class Health : MonoBehaviour
4.     {
5.         [SerializeField] float _maxValue = 40f;
6.         [SerializeField, ReadOnly] float _currentValue = 40f;
7.     }

and this

Code (csharp):

1. PropertyAttribute
2.     using UnityEngine;
3.  
4.     public class ReadOnlyAttribute : PropertyAttribute
5.     {
6.     }

but VS and Unity said "Name or namespace could not be found".
I tried much solutions given in other questions, nothing worked. Can you help me?

-- Edit

This is my folder tree:
/Assets/Scripts/UnitComponents/Health.cs
/Assets/Scripts/Editor/Attributes/ReadOnlyAttribute.cs

 

Unity compiles scripts into default assemblies if you don't define your own, the main two being Assembly-Csharp and Assembly-Csharp-Editor. Files in folders with 'Editor' are compiled into the latter; read more here: https://docs.unity3d.com/Manual/ScriptCompileOrderFolders.html

Two assemblies can't each reference each other, only in one direction, so the editor assembly references the regular one. Thus, the normal one can't know anything about the editor assembly.

Your attribute will be in the regular assembly, just like Unity's attributes are as well.

 

Oh... I feel so dumb... I was going for Attributes like I usually go for Drawers and Editors...

Thank you so much!

 

No problem! Easy mistake to make the first time.

You can decorate attributes with

[System.Diagnostics.Conditional("UNITY_EDITOR")]

to prevent them being compiled into the built game, which I use for most of my attributes.

 

Yeah, for sure. Only it was not the first time XD.

Ty for Decorate, I didn't know it!