Editor script using ReplacePrefab resetting all instanced prefabs

[Chris42]

I have written a type of data importer which is designed to grab values from XML files and load them onto prefabs. The general idea is

• Load a ‘base’ prefab (the model which has been imported previously with a script or two attached)
• Grab a bunch of data from the XML and add Components and set their values correctly
• Replace the existing prefab in the asset library with the version that has just been created

The basic script components look like:

    // Load the Base prefab
    				var basePrefab = AssetDatabase.LoadAssetAtPath("Assets/Resources/basePrefabs/" + 
    					node.SelectSingleNode("BasePrefab").InnerText +".prefab",Transform);

// -----------------------
// Add many things in here
// -----------------------
    
    // look for a prefab of similar name
    				if (AssetDatabase.LoadAssetAtPath("Assets/GamePrefabs/Ships/"+curShip.scriptName +".prefab" , GameObject))
    				{
    					 // if we found it, just replace
    					 var fab = AssetDatabase.LoadAssetAtPath("Assets/GamePrefabs/Ships/"+curShip.scriptName +".prefab" , GameObject);
    					 curShip.prefabObj = EditorUtility.ReplacePrefab(obj.gameObject,fab,ReplacePrefabOptions.ConnectToPrefab);
    				} else {
    					// else create a new prefab
    					fab =  PrefabUtility.CreateEmptyPrefab("Assets/GamePrefabs/Ships/"+curShip.scriptName +".prefab");
    					curShip.prefabObj = EditorUtility.ReplacePrefab(obj.gameObject,fab,ReplacePrefabOptions.ConnectToPrefab);
    			

}

This works pretty well! However there is a problem. When the script runs, it replaces the prefabs and resets all the instances completely. So for example if I have instantiated a spaceship in the scene and tweaked some of its values (even just moved it off the origin) and added a component or two, it gets completely reset. Back to the origin, all modified data reset, all added components gone.

So is there any way I can replace a prefab without nuking the data? It seems like if I do it manually (get my base prefab, type in all the values, hit Apply) that it doesn’t reset all instances. It’s rather vexing!

[Chris42]

I feel stupid. “read the documentation” is an appropriate answer (Unity - Scripting API: ReplacePrefabOptions)

For anyone else who sees this, check to see what ReplacePrefabOptions is correct for your method. Using ReplacePrefabOptions.ReplaceNameBased works.