Serialize C# Properties (how-to with code)

Hi all!

There's one particular C# feature I use a lot in my projects, and that is properties: They allow you to execute arbitrary code whenever a variable is read/written. Which is nice and leads to quite clean code.

However, Unity does not serialize properties by default. Which makes sense, since calling arbitrary code when serializing/deserializing objects probably is not a good idea.

Calling the getter/setter in editor automatically when tinkering with the inspector without the need to write a custom Editor has proven extremely useful though. I made my own implementation using PropertyDrawers. Here it is, feel free to copy and paste to your project:

Code (CSharp):

1. using System;
2. using System.Reflection;
3. using UnityEngine;
4. #if UNITY_EDITOR
5. using UnityEditor;
6. #endif
7.  
8.      [System.AttributeUsage(System.AttributeTargets.Field)]
9.     public class SerializeProperty : PropertyAttribute
10.     {
11.         public string PropertyName { get; private set; }
12.  
13.         public SerializeProperty(string propertyName)
14.         {
15.             PropertyName = propertyName;
16.         }
17.     }
18.  
19.     #if UNITY_EDITOR
20.     [CustomPropertyDrawer(typeof(SerializeProperty))]
21.     public class SerializePropertyAttributeDrawer : PropertyDrawer
22.     {
23.         private PropertyInfo propertyFieldInfo = null;
24.  
25.         public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
26.         {
27.             UnityEngine.Object target = property.serializedObject.targetObject;
28.  
29.             // Find the property field using reflection, in order to get access to its getter/setter.
30.             if (propertyFieldInfo == null)
31.                 propertyFieldInfo = target.GetType().GetProperty(((SerializeProperty)attribute).PropertyName,
32.                                                      BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
33.  
34.             if (propertyFieldInfo != null){
35.  
36.                   // Retrieve the value using the property getter:
37.                 object value = propertyFieldInfo.GetValue(target,null);
38.  
39.                 // Draw the property, checking for changes:
40.                 EditorGUI.BeginChangeCheck();
41.                 value = DrawProperty(position,property.propertyType,propertyFieldInfo.PropertyType,value,label);
42.      
43.                 // If any changes were detected, call the property setter:
44.                 if (EditorGUI.EndChangeCheck() && propertyFieldInfo != null){
45.      
46.                     // Record object state for undo:
47.                     Undo.RecordObject(target, "Inspector");
48.      
49.                     // Call property setter:
50.                     propertyFieldInfo.SetValue(target,value,null);
51.                 }
52.  
53.             }else{
54.                 EditorGUI.LabelField(position,"Error: could not retrieve property.");
55.             }
56.         }
57.  
58.         private object DrawProperty(Rect position, SerializedPropertyType propertyType, Type type, object value, GUIContent label)
59.         {
60.             switch (propertyType) {
61.                 case SerializedPropertyType.Integer:
62.                     return EditorGUI.IntField(position,label,(int)value);
63.                 case SerializedPropertyType.Boolean:
64.                     return EditorGUI.Toggle(position,label,(bool)value);
65.                 case SerializedPropertyType.Float:
66.                     return EditorGUI.FloatField(position,label,(float)value);
67.                 case SerializedPropertyType.String:
68.                     return EditorGUI.TextField(position,label,(string)value);
69.                 case SerializedPropertyType.Color:
70.                     return EditorGUI.ColorField(position,label,(Color)value);
71.                 case SerializedPropertyType.ObjectReference:
72.                     return EditorGUI.ObjectField(position,label,(UnityEngine.Object)value,type,true);
73.                 case SerializedPropertyType.ExposedReference:
74.                     return EditorGUI.ObjectField(position,label,(UnityEngine.Object)value,type,true);
75.                 case SerializedPropertyType.LayerMask:
76.                     return EditorGUI.LayerField(position,label,(int)value);
77.                 case SerializedPropertyType.Enum:
78.                     return EditorGUI.EnumPopup(position,label,(Enum)value);
79.                 case SerializedPropertyType.Vector2:
80.                     return EditorGUI.Vector2Field(position,label,(Vector2)value);
81.                 case SerializedPropertyType.Vector3:
82.                     return EditorGUI.Vector3Field(position,label,(Vector3)value);
83.                 case SerializedPropertyType.Vector4:
84.                     return EditorGUI.Vector4Field(position,label,(Vector4)value);
85.                 case SerializedPropertyType.Rect:
86.                     return EditorGUI.RectField(position,label,(Rect)value);
87.                 case SerializedPropertyType.AnimationCurve:
88.                     return EditorGUI.CurveField(position,label,(AnimationCurve)value);
89.                 case SerializedPropertyType.Bounds:
90.                     return EditorGUI.BoundsField(position,label,(Bounds)value);
91.                 default:
92.                     throw new NotImplementedException("Unimplemented propertyType "+propertyType+".");
93.             }
94.         }
95.  
96.     }
97.     #endif
98.  

Usage:

Code (CSharp):

1.  
2. class PropertySerializationTest : MonoBehaviour{
3.  
4.         [SerializeProperty("Test")] // pass the name of the property as a parameter
5.         public float test;
6.  
7.         public float Test{
8.             get{
9.                 Debug.Log("Getter called");
10.                 return test;
11.             }
12.             set{
13.                 Debug.Log("Setter called");
14.                 test = value;
15.             }
16.         }
17. }

 

Its working. I'm so happy about that ). Thank you @arkano22

 

With C# version > 7.3, there is a very neat trick to expose auto-properties. All auto properties have a backing field, so all you have to do is mark that field with SerializeField like this:

Code (CSharp):

1. [field: SerializeField]
2. public float Speed { get; set; }

Note: u have to use "field: ". This syntax tells compiler that all attributes in that block refer to backing field.

 

Neat indeed! However, functionally speaking this is basically the same as having a public field, am I right? No custom set/get code called during serialization...

 

I agree that being able to expose properties is extremely useful!

One common use case is exposing settings properties, and applying their effects to all affected systems whenever their value is changed.

It also makes it trivial to expose EditorPrefs and PlayerPrefs in the inspector as if they were normal fields.

[field: SerializeField] is pretty useful, as it can be used to serialize properties and expose them in the inspector with minimal boilerplate code.

The main benefit it offers over using normal fields is that you can restrict the accessibility of the set accessor.

Code (CSharp):

1.  
2. // You can look, but you can't touch!
3. [field: SerializeField]
4. public int Value
5. {
6.     get;
7.     private set;
8. }

So functionally it is very similar to having this:

Code (CSharp):

1. [SerializeField]
2. private int _value;
3.  
4. // You can look, but you can't touch!
5. public int Value
6. {
7.     get
8.     {
9.         return _value;
10.     }
11.  
12.     private set
13.     {
14.         _value = value;
15.     }
16. }

Unfortunately the property backing field will have a very ugly label in the inspector by default, which is something you'll need to fix before it really becomes a usable solution.

This is how it looks in the inspector by default (the one on the left):

 

Any idea how to get this to work with a custom struct?

 

Found that it's not working like this, because

can't found property, any suggestion how to fix?

 

row and column aren’t properties, nor backing fields of a property. They’re just public variables, you don’t need to do anything special for them to be serialized.

This method is intended to deal with properties.

 

Interesting. @arkano22 does this need the backing field to be set to public? Doesn't this defeat part of the point of using properties, which is keeping our fields private and controlling their access?

EDIT: Nevermind, I figured out I can just have my field private and add the [SerializeField] attribute together with the [SerializeProperty()] one.

Great stuff!

 

@arkano22 do the SerializeProperty and SerializePropertyAttributeDrawer classes need to be in the same script as the class in which you'd like to use SerializeProperty()?

I created a script with your first code block, then I created a second script following your PropertySerializationTest. The problem is I can't use [SerializeProperty()] in that second script; I'm getting a "missing type or namespace" error for SerializePropertyAttribute and SerializeProperty.

I feel like I'm missing something basic here, but I'm at the edge of my programming knowledge with this one.

 

@reinfeldx Scripts placed inside a folder named Editor are not visible to other scripts, that is probably the source of your issues.

Good practice would be to split the code into two separate files: one containing just the SerializeProperty class and another file one containing just the SerializePropertyAttributeDrawer class. The SerializePropertyAttributeDrawer.cs file should then be placed inside an Editor folder while the SerializeProperty.cs file should not be inside an Editor folder. This is because the drawer is only needed in the editor while the attribute might be used within classes that exist in builds too.

There's an example in the manual under Customize the GUI of script members using Property Attributes.

 

In Unity 2020 you can use

Code (CSharp):

1. [field: SerializeField]

 

I guess they fixed the backing-field name issue above?
When did they do that?

 

Why does

private set

is required? Resharper says it is redundant but unity won't parse it without that (However, in versions before 2020 it worked). I had to switch that inspection off, pretty silly

 

Is there a way to use your SerializeProperty class with lists or arrays?

 

Thanks very much. Super useful!

Edit: @arkano22 I can't get it working with int :/ I might be doing something wrong though.

Code (CSharp):

1. [SerializeProperty("Min")] public int minimum;
2.        
3.         public int Min
4.         {
5.             get => _min;
6.             set => Set(value, _max);
7.         }

it just returns the error of not being able to retrieve. I am using Unity 2019.4.14f1

 

Please start your on fresh post with all the information needed.

How to report your problem productively in the Unity3D forums:

http://plbm.com/?p=220

How to understand errors in general:

https://forum.unity.com/threads/ass...3-syntax-error-expected.1039702/#post-6730855

The first error I see is, "What on earth is

_min

and

_max

in your code?"

 

I had a similar issue. I had a scriptable object that was referencing properties from a namespaced script.
I thought it was the fact the properties where not in classes and instead just in namespaces, that that was the issue.
As others have said, it turned out to be just simply adding [field: SerializeField] to each property did the trick.
In the inspector, the label will look ugly, but just make a custom editor for that.

Also note that if your scriptable object is stored as a .asset file, don't forget to set the object as dirty and save the asset database.

 

Has anyone found a way to use this together with validation code? Can't seem to get this working when "expanding" the getter/setter methods.

For instance, I've tried to make a small class that makes sure an AudioClip is ambisonic (as that sometimes takes us by surprise during importing);

Code (CSharp):

1. [Serializable]
2. public class AmbisonicAudioClip : ISerializationCallbackReceiver
3. {
4.     [SerializeField]
5.     private AudioClip clip;
6.  
7.     public AudioClip Clip
8.     {
9.         get => clip;
10.         set
11.         {
12.             clip = value;
13.             ValidateClip();
14.         }
15.     }
16.  
17.     public void OnAfterDeserialize()
18.     {
19.        
20.     }
21.  
22.     public void OnBeforeSerialize()
23.     {
24.         ValidateClip();
25.     }
26.  
27.     private void ValidateClip()
28.     {
29.         if(clip)
30.             if (!Clip.ambisonic)
31.                 Debug.LogError("Clip " + clip.name + " is not ambisonic!");
32.     }
33. }

This works fine but looks bad in the editor, and I can't serialize the public property...

 

I just autocompleted my way to this thing here:

[field: SerializeField] public int CurrentVoxelCount { get; private set; }

That is exposed in the inspector.

 

This is cool, thanks @arkano22 !

I got it working on a regular script - very nice indeed.

I tried to add it to a [serializable] class that is being displayed as part of a larger class in the inspector, but it didn't like that.
Looks like this line in the code is getting confused, since the the target here is returning the larger class, rather than the initial serialized class with the property on it.

Code (CSharp):

1. UnityEngine.Object target = property.serializedObject.targetObject;

If anyone has thought about how to fix this and come up with a solution I would love to hear it! I might do some thinking on it later.

 

This only works for auto properties, as all it does is serialize their backing field (handy when you want to have a read-only property, though). You can't insert arbitrary code in the getter/setter, which is what the solution presented in this thread is intended for and the whole point of using properties.

 

Is there a way to do this without creating a field? I wanna add a property that does not have a backing field. With this method, I can add a fake field for this property to show in the inspector. Also, the field has to be public, which is another problem.

 

What do you mean you don't want a backing field? all properties have a backing field, even auto-properties (though in their case, the compiler automatically creates the field under the hood).

Properties are just syntactic sugar for getters/setters. You need to store their value somewhere, it's just not possible to have a property with no backing field. If you meant an auto property, you can use [field:SerializeField] as pointed out above.

 

Auto-properties are just a subtype of properties. Some properties can be just accessors to something.

The example is not ideal.
Does anyone know if there is a way to make Unity serialize properties?

 

Oh, I see. You can only serialize data. A property that basically acts as a getter/setter for your own data, still has a “backing field” of sorts, even if it’s more complex than a single string/integer/etc. So you either serialize that data, or all you have is a couple methods. In your example, this data is a reference to the TextMeshPro component.

So you want a property that shows up in the inspector, isn’t serialized (saved), and all you need is the getter/setter to be called when its data is changed in the inspector via UI. Correct? In that case you’ll need to use a custom editor I think, and manually set/get your property there using editor fields.

 

this is pretty cool, One problem though : doesnt work with the undo function in the editor.

 

what I mean is that this does not call the setter on Undo/Redo.

 

Now that Unity officially support most of the C# 9 features like records, does someone knows how to serialize properties with a init only setter?

The trick with [field: SerializeField] does not seem to work; it doesn't work on properties with no setter or a implicit private setter either, but works if the setter is explicitly flagged private.

 

This is real progress, but most of my usage of properties is to call validating and housekeeping code related to the change in the value.

[field: SerializeField]

doesn't support this.

As an example, I'm working with a GameObject right now that has multiple layers, with procedural properties to their scale and rendering, controlled by the parent; it would be easy, from a coding perspective, to monitor the number-of-layers property for changes and bolster or trim the child objects automatically; but the moment I add anything other than autoproperty code, the inspector stops showing the property.

That basically means I've got to disregard the entire inspector to do it like this, even though it keeps my code much cleaner (and depending on the chosen workaround, more efficient, too).

So, I would politely argue that the feature is ultimately half-finished.

 

I noticed that following code does not work in 2021.3.12

Code (CSharp):

1. #if UNITY_EDITOR
2.  
3. [CustomEditor(typeof(SceneGroupList))]
4. public class SceneGroupListEditor : Editor
5. {
6.     private SceneGroupList _sceneGroupList;
7.     void OnEnable()
8.     {
9.         _sceneGroupList = target as SceneGroupList;
10.     }
11.  
12. [System.Serializable]
13. public class SceneGroup
14. {
15.     [field: SerializeField] public uint Idx { get; set; }
16. }
17.  
18. public override void OnInspectorGUI()
19. {
20.     serializedObject.Update();
21.     for (var i = 0; i < len; i++)
22.     {
23.         var arrayElement = property.GetArrayElementAtIndex(i);
24.         DrawSceneGroup(arrayElement, _sceneGroupList.SceneGroups[i]);
25.     }
26. }
27.  
28. private void DrawSceneGroup(SerializedProperty arrayElement, SceneGroup sceneGroup)
29. {
30.     EditorGUILayout.Space();
31.     EditorGUILayout.BeginVertical(GUI.skin.box);
32.  
33.     EditorGUILayout.PropertyField(arrayElement.FindPropertyRelative("Idx"));
34.  
35.     EditorGUILayout.EndVertical();
36. }
37.  
38. }
39.  
40. #endif

But changing "[field: SerializeField] public uint Idx { get; set; }" line into

Code (CSharp):

1. public uint Idx;

works.

 

Wow, thanks for this solution.
However, when trying to use it combined with the [Range(min,max)] attribute it doesn't work anymore.

Code (CSharp):

1.  
2.         [Range(0, 3), SerializeField, SerializeProperty("Channel")]
3.         private int m_channel = 0;
4.         public int Channel
5.         {
6.             set
7.             {
8.                 if (m_channel != value)
9.                 {
10.                     m_channel = value;
11.                     m_propertyBlock.SetInt("_Channel", m_channel);
12.                 }
13.             }
14.             get { return m_channel; }
15.         }

The above example shows the range attribute in the inspector, but the setter isn't called anymore when changing the "Channel" value. When moving the Range attribute to the end "[SerializeField, SerializeProperty("Channel"),Range(0, 3)]", the setter still gets called, but the slider does not show up in the inspector.

Any idea how to fix this?

 

You can't combine multiple property drawers on a single member variable. One attribute will take precedence and the others will be ignored, otherwise you'd be drawing the same property multiple times.

As with pretty anything in Unity, you can work around this limitation by writing your own drawer system. See the following thread for more info on an approach that composes multiple property drawers: https://forum.unity.com/threads/drawing-a-field-using-multiple-property-drawers.479377/