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How is fileID generated for m_CorrespondingSourceObject ?

Discussion in 'Prefabs' started by pushxtonotdie, Aug 12, 2019.

  1. pushxtonotdie


    Oct 21, 2010

    I'm investigating an issue with prefab variants and and attempting to determine what is going on. If I do make some progress on this I will hopefully be able to create a repro (or perhaps you can tell me this is fixed in a later version of Unity and I can just upgrade).

    The issue is this: I have a prefab with a prefab variant nested inside it. I created this variant, added it, then connected up to the code via a reference. This created the following code at the bottom of the parent prefab:

    Code (csharp):
    2. --- !u!114 &3075605346730906691 stripped
    3. MonoBehaviour:
    4.   m_CorrespondingSourceObject: {fileID: 6933667124208082087, guid: 583b983315f544810b2693d460bcfcde,
    5.     type: 3}
    6.   m_PrefabInstance: {fileID: 5375023374358153444}
    7.   m_PrefabAsset: {fileID: 0}
    8.   m_GameObject: {fileID: 0}
    9.   m_Enabled: 1
    10.   m_EditorHideFlags: 0
    11.   m_Script: {fileID: 11500000, guid: 461fcabef184540deb0b87352712d1dd, type: 3}
    12.   m_Name:
    13.   m_EditorClassIdentifier:
    For whatever reason the fileID of 6933667124208082087 is incorrect. The correct number is 7038841995742994224. I determined this by copying the project except the Library/ and then re-attaching the script reference. I also did a Reimport All after I knew the correct value and found my original project broke in the same way. But why the fileID is incorrect I cannot understand, partially because I don't know how its generated. How is it made?
  2. SteenLund


    Unity Technologies

    Jan 20, 2011

    For variants the FileID is the
    (FileID_of_PrefabInstance_in_variant ^ FileID_of_object_in_base_Prefab) & 0x7fffffffffffffff;
    Jojo59516_2 and chengyingzhilian like this.
  3. pushxtonotdie


    Oct 21, 2010
    That was very, very helpful to know Steen, I appreciate it. While this dramatically sped up my bughunting this morning, I unfortunately could not get a repro. All my file id hashes checked out, and I couldn't find anything that matched the bad fileID of 6933667124208082087. What I did learn is that the FileID_of_PrefabInstance_in_variant is 6933667124208079258, which is 2829 off from the bad fileID. Those numbers are really close but I can't make heads or tails of it. I will have to file this under 'until next time it happens'.