Changing object instance in custom editor does not apply modifications to prefab

I've been having issues with the new prefab workflow where changing the target value in an editor outside of SerializedObject does not apply modifications. In the past using EditorUtility.SetDirty(target) was enough to have the modifications apply.

The below editor works correctly outside of prefab mode, but in prefab mode the change to Value (from pressing the button) is not written to disk.

Any ideas? Thanks.

Code (csharp):

1. using UnityEditor;
2. using UnityEngine;
3.  
4. public class Demo : MonoBehaviour {
5.   public int Value;
6. }
7.  
8. [CustomEditor(typeof(Demo))]
9. class DemoEditor : Editor {
10.   public override void OnInspectorGUI() {
11.     if (GUILayout.Button("Generate new value")) {
12.       ((Demo)target).Value = Random.Range(0, 10000);
13.       EditorUtility.SetDirty(target);
14.     }
15.  
16.     DrawDefaultInspector();
17.   }
18. }

 

Ah, got it. For future reference you need to mark the scene as dirty.

Code (csharp):

1. var behavior = target as MonoBehaviour;
2. if (behavior)
3.   EditorSceneManager.MarkSceneDirty(behavior.gameObject.scene);

https://forum.unity.com/threads/saving-prefab-after-contextmenu-change.599389/ also has lots of helpful tips.