Unity Interface Serialization-Expose Interface field In Inspector

Posted 2020-06-16

Unity has some quirks about their inspector, so as a preface they are listed here:

• If you add a [Serializable] attribute to a class, Unity‘s Inspector will attempt to show all public fields inside that class.
• Any class extending Monobehaviour automatically has the [Serializable] attribute
• Unity‘s inspector will attempt to display any private field with the [SerializeField] attribute.
• Unity‘s inspector will not attempt to display generic types or interfaces, with the exception of List<T>, which is hard-coded.
• Unity‘s inspector will not attempt to display properties. A common workaround is to have a private backing field for your property with [SerializeField] attached. Setters won‘t be called on the value set in the inspector, but since that‘s only set pre-compilation, that‘s acceptable.
• Unity has a PropertyDrawer class you can extend to control how a type is displayed in the inspector. The PropertyDrawer for an interface or generic type will be ignored.

When we want to Serialize the Interface,What we can do？

Unity, by itself, does not expose fields that are of an interface type. It is possible to manually enable this functionality by implementing a custom inspector each time as Mike 3 has pointed out,but even then the reference would not be serialized ("remembered" between sessions and entering/exiting playmode).

It is possible however to create a serializable container object that wraps around a Component field (which is serialized) and casts to the desired interface type through a generic property. And with the introduction of custom property drawers into Unity, you can effectively expose a serialized interface field in your scripts without having to write a custom inspector / property drawer each time.

Some simple demo code :

using UnityEngine;

[System.Serializable]
public class InterfaceHelper  {

	public Component target;

	public T getInterface<T>() where T : class
	{
		return target as T;
	}
}

And the Custom property drawer:

using UnityEngine;
using UnityEditor;

[CustomPropertyDrawer(typeof(InterfaceHelper))]
public class EditorInterfaceHelper : PropertyDrawer {

	public override void OnGUI(Rect pos, SerializedProperty prop, GUIContent label)
	{
		EditorGUI.BeginProperty(pos, label, prop);
		pos = EditorGUI.PrefixLabel(pos,GUIUtility.GetControlID(FocusType.Passive),label);
		EditorGUI.PropertyField(pos,prop.FindPropertyRelative("target"),GUIContent.none);
		EditorGUI.EndProperty();
	}
}

Usage:

public interface IData
{
	void getData();
}

#define
public InterfaceHelper dataSrc;
...
//call the function
dataSrc.getInterface<IData>().getData();

The interface field in inspector is like this:

Of course， You can use abstract class instead sometimes,but if you do that, you will miss the benefit of mul-inherit.

參考：

http://codereview.stackexchange.com/questions/65028/inspector-interface-serializer

http://answers.unity3d.com/questions/46210/how-to-expose-a-field-of-type-interface-in-the-ins.html

http://answers.unity3d.com/questions/783456/solution-how-to-serialize-interfaces-generics-auto.html