Question Call method when dropdown item is selected in Inspector

I would like a method to be called every time I select a value from a dropdown in the Inspector. Is this possible?

Code sample:

Code (CSharp):

1. public class Animal : MonoBehaviour
2. {
3.     public enum AnimalType
4.     {
5.         Dog, Cat, Hamster, Bunny,
6.     }
7.  
8.     [SerializeField] private AnimalType animalType;
9.  
10.     // TODO: Call this function every time I select a value
11.     // from the enum dropdown in the Inspector.
12.     private void OnAnimalSelected() { }
13. }

 

Think you might be looking for this.

https://docs.unity3d.com/ScriptReference/MonoBehaviour.OnValidate.html

 

Thanks, but that one gets called more often than I need it to be. It also gets called very early, seemingly before Awake, and because of that I cannot access components in it that I have set with GetComponent in Awake.

 

The answer is via a custom inspector.

 

You can achieve this with a custom property attribute and property drawer.

Something like this:

Code (CSharp):

1. [AttributeUsage(AttributeTargets.Field), Conditional("UNITY_EDITOR")]
2. public sealed class OnValueChangedAttribute : PropertyAttribute
3. {
4.     public string MethodName { get; }
5.  
6.     public OnValueChangedAttribute(string methodName) => MethodName = methodName;
7. }

Code (CSharp):

1. [CustomPropertyDrawer(typeof(OnValueChangedAttribute))]
2. public class OnValueChangedAttributeDrawer : PropertyDrawer
3. {
4.     public override VisualElement CreatePropertyGUI(SerializedProperty property)
5.     {
6.         var result = new PropertyField(property);
7.         result.RegisterValueChangeCallback(OnValueChanged);      
8.         return result;
9.  
10.         static void OnValueChanged(SerializedPropertyChangeEvent @event)
11.         {
12.             const BindingFlags flags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;
13.             var serializedProperty = @event.changedProperty;
14.             var targets = serializedProperty.serializedObject.targetObjects;
15.             var type = targets.First().GetType();
16.             var field = type.GetField(serializedProperty.name, flags);
17.             var attribute = field.GetCustomAttributes(typeof(OnValueChangedAttribute), false).First() as OnValueChangedAttribute;
18.             var method = type.GetMethod(attribute.MethodName, flags);
19.             Undo.RecordObjects(targets, "On Value Changed");
20.             foreach(var target in targets)
21.             {
22.                 var parameters = method.GetParameters();
23.                 switch(parameters.Length)
24.                 {
25.                     case 0:
26.                         method.Invoke(target, null);
27.                         break;
28.                     case 1 when parameters[0].ParameterType is Type parameterType:
29.                         if(parameterType == typeof(SerializedProperty))
30.                         {
31.                             method.Invoke(target, new object[] { serializedProperty });
32.                         }
33.                         else
34.                         {
35.                             method.Invoke(target, new object[] { field.GetValue(target) });
36.                         }
37.                         break;
38.                 }
39.             }
40.             serializedProperty.serializedObject.Update();
41.         }
42.     }
43. }

And usage:

Code (CSharp):

1. [OnValueChanged(nameof(OnValueChanged))]
2. private float value;
3.  
4. private void OnValueChanged(float value)
5. {
6.     Debug.Log("Value changed to: " + value);
7. }