I am getting the following warning in the Xcode console while running (not compiling) my application since updating to High Sierra on my MacBook:
objc[26299]: Class FIFinderSyncExtensionHost is implemented in both /System/Library/PrivateFrameworks/FinderKit.framework/Versions/A/FinderKit (0x7fff88339a70) and /System/Library/PrivateFrameworks/FileProvider.framework/OverrideBundles/FinderSyncCollaborationFileProviderOverride.bundle/Contents/MacOS/FinderSyncCollaborationFileProviderOverride (0x10cae0cd8). One of the two will be used. Which one is undefined.
I found the someone else getting this warning on Github, and someone who is getting it when working with Java: Java Exception since Mac OS High Sierra
To me the problem behaves exactly as described in the discussion on Github. It doesn't seem to produce any functional issues directly connected to it. In my case I would like to get rid of all warnings though because I am experiencing issues with my application since I updated to High Sierra.
I hope someone has found a way to tackle this warning by now.
There's nothing you can do about this. It's an Apple problem, but it's probably harmless.
Note: I'm not sure what other description could be given than what the warning says. It just means that the same class is defined in two modules. With Apple stuff, they're often identical so it doesn't matter which copy is used.
来源：https://stackoverflow.com/questions/46999695/class-fifindersyncextensionhost-is-implemented-in-both-warning-in-xcode-si