I found the solution for checking if a gameobject is "prefab ghost" or not!!!

* You can go to Edit 3 directly for solution.
* Read Edit 2 for explanation.

Edit:
Today I found out about GameObject.hideFlags so it can be used for finding if the gameobject is prefab or not. if hideFlags is HideInHierarchy then it's a prefab.
Please ignore the rest of this post...

Edit 2:
1) I take back my first edit because hideFlags can't be used for this purpose. The real gameobjects can also be hidden in hierarchy and that doesn't mean they are prefabs.

2) I have to make some clarifications. The code hereby has nothing to do with the prefab files in your project or prefab instances in your scene. It solves another problem about the ghost prefabs which lives only in runtime. As we all know, there is no prefab concept in runtime. Evertything is regular gameobject in runtime including the prefabs in your project folder. Well, they are not so regular because they don't live inside the scene, they are not visible, they don't receive the events like start, update, etc.. but still, they are just hidden gameobjects which are waiting to be instantiated by your command. So they are like ghost objects and my code below tries to distinguish those ghost objects from the real scene objects. From now on, I'll call them as "prefab ghosts" and I'll update the title of this post.

3) Unity has a bug about GetSiblingIndex method. It works fine in editor (both edit and play modes) but it always returns zero in build runtime only for scene root objects. It works fine for non-root game objects in runtime too. So the code below doesn't work for root objects in build runtime until Unity team fixes this bug.

Edit 3:

Code (CSharp):

1.  
2.         /// <summary>
3.         /// Play mode only!
4.         /// </summary>
5.         public static bool IsPrefab(this Transform This)
6.         {
7.             if (Application.isEditor && !Application.isPlaying) throw new InvalidOperationException(Strings.MethodIsOnlyAllowedInPlayMode("IsPrefab"));
8.  
9.             return This.gameObject.scene.buildIndex < 0;
10.         }
11.  

How to use...

Code (CSharp):

1.  
2.        if (transform.IsPrefab()) print("this is a prefab ghost which is invisible and lives in runtime silently");
3.  

---------------------
Original post(Obsolete):

I finally found a better way than searching through all scene objects... (Play mode only)

Code (CSharp):

1.  
2.     static class TransformExtensions
3.     {
4.         internal static bool IsPrefabGhost(this Transform This)
5.         {
6.             var TempObject = new GameObject();
7.             try
8.             {
9.                 TempObject.transform.parent = This.parent;
10.  
11.                 var OriginalIndex = This.GetSiblingIndex();
12.  
13.                 This.SetSiblingIndex(int.MaxValue);
14.                 if (This.GetSiblingIndex() == 0) return true;
15.  
16.                 This.SetSiblingIndex(OriginalIndex);
17.                 return false;
18.             }
19.             finally
20.             {
21.                 Object.DestroyImmediate(TempObject);
22.             }
23.         }
24.     }
25.  

How to use...

Code (CSharp):

1.  
2.        if (transform.IsPrefabGhost()) print("this is a prefab ghost which is invisible and lives in runtime silently");
3.  

 

So I gave this a try using:

Code (csharp):

1.  
2.     [MenuItem("Test/Selection Is Prefab")]
3.     public static void CheckPrefab() {
4.         Debug.Log(Selection.activeTransform.IsPrefab());
5.     }

Selecting a non prefab in the scene and running this logged False.
Selecting a prefab in the scene logged False.
Selecting a prefab in the project view caused a null reference exception.

How is this supposed to work?

 

Or just...
http://docs.unity3d.com/ScriptReference/PrefabUtility.GetPrefabParent.html
check if null

 

hpjohn, PrefabUtility is editor only. My version is for runtime.

 

ThermalFusion, I'm happy you tested it. I'll check what's wrong...

 

ThermalFusion, I see the problem with your test. My code is for play mode only because in editor mode we have other options for a long time. But I didn't see any solution for play mode until now.

In play mode, there is no "REAL" prefabs. Everything is gameobject. Even the prefab instances in your scene becomes regular gameobjects when you start play mode. And also, your prefabs in the project tree are created as regular gameobjects in play mode. But they don't appear in the scene. So my function can distinguish the difference between the gameobjects in the scene and gameobject off the screen (formerly prefabs in edit mode).

I checked your tested myself...

1) Non-prefab in scene logs as false and this is correct.
2) Your second test returns false because any object in the scene is not a prefab even if they are in blue color. They are instances of prefabs and instances are gameobject actually. This is also correct.
3) When you select a prefab in the project window, Selection.activeTransform is null. that's why you got Null exception. Not because of my code.

 

I'm curious what problem you're solving by determining if something is a prefab or not while the game is playing.

 

I'm developing a small plugin which sends message to all objects even if they are inactive in the scene. Because default SendMessage doesn't work on inactive objects. For the purpose of my plugin, In play mode, I should know the difference between real scene objects and "off scene" objects (which were prefabs in project folder in edit mode). So I don't send the message to prefabs because they should be notified in any way. They are just off scene objects.

It's actually more complicated but I don't list all the details here.

When I finish this, It will be free in asset store and I think many people will be happy to be able to send messages to inactive scene objects

 

There was no mention in the original post that it was during runtime only. I'll call these runtime instances of prefabs "prefab" from now on.
So I see what you're doing now, you're forcibly changing the hierarchy order and seeing if it changes, which it can't if it's not an object in the scene.
Here's a variation I tried that uses the root transform of an object instead and doesn't touch the "prefab":

Code (csharp):

1.     internal static bool IsPrefab(this Transform This)
2.     {
3.         bool result = false;
4.         GameObject tempObject = new GameObject();
5.         Transform rootObject = This.root;
6.         tempObject.transform.SetAsFirstSibling();
7.         if (rootObject.GetSiblingIndex() == 0) result = true;
8.         Object.DestroyImmediate(tempObject);
9.         return result;
10.     }

This should not throw an exception on trying to modify a "prefab".

A couple of notes:
As per the documentation, one should not call DestroyImmediate in runtime, only in editor.
Modifying the hierarchy order of the scene could possible have overhead, one would have to profile this.

 

If the scene object is the only child of a parent (or in a scene root), SetSiblingIndex doesn't work. This is why I am creating the temp object as a potential sibling to the actual object (which is "This").

I don't see any link between the temp object and the actual object in your code because you didn't set its parent to actual object's parent. They are not siblings and I don't understand why are you creating it.

I was hesitant to user DestroyImmediate but since I created the temp object in the same method, it should give any trouble I suppose.

Yes I'm very well aware of SetSiblingIndex may have an overhead in runtime but it is much much better than searching through all the objects in a big fat scene.

Thank you for your comments and suggestions. That's the only way I can improve my code and my self.

 

You see I always compare the root transform of This. A root in a "prefab" will never have any siblings where a root in the scene can. So I create a new object in the scene, make it the first sibling, then see if this.root still is alone, then we can guess its a prefab.

 

What if the scene object is child of another object and still have no siblings? Root can help here but it's overhead is bigger I guess. Both methods should be tested.

 

FindObjectsOfType let you collect all scene objects doesn't it ? If you afraid of performance cost, you could convert it to a HashSet to get quick check.

Code (CSharp):

1. HashSet<UnityEngine.Object> sceneObjects = new HashSet<UnityEngine.Object>();
2.  
3. void Start()
4. {
5.     foreach (UnityEngine.Object obj in FindObjectsOfType<UnityEngine.Object>())
6.         sceneObjects.Add(obj);
7. }
8.  
9. public bool IsPrefab(UnityEngine.Object obj)
10. {
11.     return !sceneObjects.Contains(obj);
12. }

What do you think ?

 

I wouldn't even think about storing all the scene objects in a data structure for a big game. For small games, your approach is doable. But I wanted to support very big scenes.

 

This looks to be a bit inneficient if you're going to create a new GameObject and destroy it every time you test if its a prefab or not...

 

Yes but it's still better than using FindObjectsOfType. Right ?

 

I could be missing something, but this small script worked for me so far very well

Code (csharp):

1.  
2. [DisallowMultipleComponent, ExecuteInEditMode]
3. public class PrefabMarker : MonoBehaviour
4. {
5.    private bool _isInScene;
6.  
7.    public bool IsInScene
8.    {
9.      get { return _isInScene; }
10.    }
11.  
12.    void Awake()
13.    {
14.      _isInScene = true;
15.    }
16. }
17.  

Came across the idea in Mike's Unity Serializer. You should attach this script to a prefab object from your project window, i.e. not a prefab instance. It seems that even though the script has ExecuteInEditMode on it, Awake doesn't get called when you attach the script to a prefab. The flag becomes true immediately when you instantiate the prefab (in edit or playmode). You can make the flag public just to see how the value changes yourself.

 

Code (CSharp):

1.     void Start () {
2.         Debug.Log(transform.IsPrefab());
3.     }

I tested.
runtime add this script to a prefab. but It's all return false ?

 

oh I konw.
It's must before Instantiate
thank you ~

 

I updated the original post for more information.

 

The problem is, FindObjectsOfType() will return active objects only.

 

This does not work on Android. Calling GetSiblingIndex() on root objects will return 0 always.

 

This is a SERIOUS bug and it's not only on Android. It happens on all platforms other than editor. I reported that bug months/years ago. Unity team confirmed it but didn't fix yet

It would be good if you vote for it : http://issuetracker.unity3d.com/issues/getsiblingindex-always-returns-zero-in-standalone-builds

 

Hide flags might work but not on GO but GO.transform.hideFlags==HideFlags.HideInHierarchy = is Prefab. Not working in IOS, as probably something is different there...

 

I updated my method long time ago. I will add it in the original post up there now.

 

What is the link of original post?

 

It's in this thread. Check the Original post(Obsolete) section in the first post.

 

Just posting a few years later to thank you because this worked beautifully

 

Now it doesn't work correctly. Immortalized objects (marked as DontDestroyOnLoad) are placed into DontDestroyOnLoad scene which has build index -1. So this method is not suitable for such objects. Probably it would be better to use Scene.IsValid() function. But I'm not sure about anything now.

Ah, does anybody know analogous solution for ScriptableObjects?

 

This also won't work if you're just playing a scene in the editor that isn't in the build list

 

I've just checked that and it works fine. The buildIndex property returns non-zero value. But what will happen if you do this in runtime for scenes loaded from asset bundles?

 

But do they return a positive value? I haven't tried this, but I would assume that in a scene that's not in the build list, every single object would have a negative buildIndex value, which would break the intended behavior since they're not "prefab ghosts" but scene objects. If they return any non-negative number, isn't that a bug?

 

Isn't it better to use

PrefabAssetType

I haven't tried it, but I think this should work

Code (CSharp):

1. using UnityEngine;
2. using UnityEditor;
3. // ...
4.  
5. if(PrefabUtility.GetPrefabAssetType(GO) == PrefabAssetType.NotAPrefab){
6.     //.. Whatever you want to do
7. }

 

From the 4th post in this thread (which was also 5 years ago)

 

Oh, my bad. Didn't notice that.