Question by jklw10 · Apr 10, 2020 at 12:33 AM · scripting problem propertydrawer customization onscenegui

how do i draw something in the scene for a property

i'm trying to make an attribute that i can add for anything be it monobehaviour or scriptable object that when it's property is drawn it draws something in the scene, currently the drawing part works but after closing the property drawer the custom OnSceneGui function is not removed from the scene and causes a null exception error (even though there's a null check) here's the most working version:

 [CustomPropertyDrawer(typeof(DraggablePoint), true)]
 public class DraggablePointDrawer : PropertyDrawer
 {
 
     SerializedProperty Prop;
 
     private void OnSceneGui(SceneView obj)
     {
         //SceneView.duringSceneGui -= OnSceneGui;
         
         Handles.color = Color.green;
         int id = GUIUtility.GetControlID(FocusType.Passive);
         if (Prop is object)
         {
             Handles.SphereHandleCap(id, Prop.vector3Value, Quaternion.identity, 1, EventType.Repaint);
             Prop.vector3Value = Handles.PositionHandle(Prop.vector3Value, Quaternion.identity);
         }
 
        // SceneView.duringSceneGui -= OnSceneGui;
     }
 
     public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
     {
         EditorGUILayout.PropertyField(property);
         if (fieldInfo.FieldType == typeof(Vector3))
         {
             Prop = property;
             SceneView.duringSceneGui -= OnSceneGui;
             SceneView.duringSceneGui += OnSceneGui;
         }//*/
         if (Prop is object)
         {
             property = Prop;
         }
         property.serializedObject.ApplyModifiedProperties();
     }
     public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
     {
         return 1;
     }
     
 }

Add comment · Show 2

zORg_alex · May 25 at 06:27 AM 0

I just bumped in the same issue. I can unsubscribe on Selection.selectionChanged. I can monitor if a value changed and I need to update the scene drawer. You can do a trick to unsubscribe when a selection is changed. I had a property with a preview in scene on mouse hover and a toggle that would keep preview on even when mouse is not hovering:

         private void SetUpPreview(bool newPreviewValue)
         {
             if (newPreviewValue != previewAlways)
             {
                 previewAlways = newPreviewValue;
                 SceneView.duringSceneGui -= _PreviewHandlesInternal;
                 if (previewAlways)
                 {
                     SceneView.duringSceneGui += _PreviewHandlesInternal;
                     Selection.selectionChanged += UnsubscribeSetUpPreview;
                 }
             }
 
             void UnsubscribeSetUpPreview()
             {
                 Selection.selectionChanged -= UnsubscribeSetUpPreview;
                 SceneView.duringSceneGui -= _PreviewHandlesInternal;
             }
         }

And yes, nested methods are a thing, so you can unsubscribe themselves, no problemo.

I wish there would be a way to get all property drawers of a type to ask them to draw from a static method, so you would do that only for active ones.

zORg_alex · May 25 at 06:33 AM 0

I bet you should check if

 if (Prop)

instead of is object. It's a UnityObject. When it's null, it's not a null really. .NET doesn't treat it as null, but fails to read any fields or call on any members. It has it's == operator overloaded.

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