XCode8 iMessage Swift 2.3 dyld: Symbol not found: __swift_getInitializedObjCClass ,Message.appex/../../Frameworks/libswiftCore.dylib

dyld: Symbol not found: __swift_getInitializedObjCClass
Referenced from: derived_path/PlugIns/Message.appex/Message
Expected In: derived_path/PlugIns/Message.appex/../../Frameworks/libswiftCore.dylib
in derived_path/PlugIns/Message.appex/Message

This problem occurs because of the difference of the target swift versions . You need to set swift version same in the both of the main target and imessage extension target.

Related apple developer forum post : https://forums.developer.apple.com/thread/48740

XCode8 How to use CocoaPod frameworks written in Swift 2.3 (CocoaPods Lagecy Swift)

If you are developing iOS apps with using XCode8 (with Swift 3.x or Swift 2.3) but your CocoaPod project always gets compile error because of your 3rd party targets implemented in Swift 2.3, you need to set SWIFT_VERSION property in build settings to '2.3'.

For dynamic frameworks, this property shown as "Use Legacy Swift Language Version" - Yes, No.

But after every pod update, CocoaPods removes this settings from Pods project and you need to set this settings again, manually.

To acheive this problem, you can use post_install script below in your Podfile :