xcode objective-c failed when building for simulator

Hi,

 

I designed a app for files access include dropbox on iphone in xcode9 with DropboxSDK.framework. The code ran on device is fine but will happen following error message when building code for simulator. Is there any solutions to solve following problem?

 

Undefined symbols for architecture x86_64:
  "_OBJC_CLASS_$_DBFILESFolderMetadata", referenced from:
      objc-class-ref in ISDropboxFileSystem.o
  "_OBJC_CLASS_$_DBFILESThumbnailSize", referenced from:
      objc-class-ref in ISDropboxFileSystem.o
  "_OBJC_CLASS_$_DBFILESFileMetadata", referenced from:
      objc-class-ref in ISDropboxFileSystem.o
  "_OBJC_CLASS_$_DBClientsManager", referenced from:
      objc-class-ref in ISDropboxFileSystem.o
      objc-class-ref in AppDelegate.o
  "_OBJC_CLASS_$_DBFILESThumbnailFormat", referenced from:
      objc-class-ref in ISDropboxFileSystem.o
  "_OBJC_CLASS_$_DBFILESCommitInfo", referenced from:
      objc-class-ref in ISDropboxFileSystem.o
  "_OBJC_CLASS_$_DBFILESDeletedMetadata", referenced from:
      objc-class-ref in ISDropboxFileSystem.o
  "_OBJC_CLASS_$_DBFILESUploadSessionCursor", referenced from:
      objc-class-ref in ISDropboxFileSystem.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)