Xcode 8 Objective-C category warning

I'm using Xcode 8 and Swift 3.0. What does this error message mean?

> ld: warning: Some object files have incompatible Objective-C category definitions. Some category metadata may be lost. All files containing Objective-C categories should be built using the same compiler.

I also had this issue in a UIColor extension, my app is entirely made with swift except for some frameworks that use Objective-c so I have no problem in declaring the var as @nonobjc:

extension UIColor {
   @nonobjc static var lol: UIColor {
      return UIColor.red
   }
}

From the apple docs: > The nonobjc attribute tells the compiler to make the declaration unavailable in Objective-C code...

Since this code is unavailable to Objective-C the warning disappears.

In my case, the reason was having computed type property in an extension:

extension NSParagraphStyle {
	class var defaultStyle: NSParagraphStyle {
		return ...
	}
}

Not sure what the exact reason behind this is, but to get rid of the warning I had to convert the computed type property (class var) to a type method (class func):

extension NSParagraphStyle {
	class func defaultStyle() -> NSParagraphStyle {
		return ...
	}
}

This warning appeared in my project after adding a framework that used Objective-C in my application that otherwise used Swift 3 entirely.

By declaring all static functions and static variables in all extensions as @nonobjc this warning went away.

For example

extension Notification.Name {
    @nonobjc static let MyNotificationName = Notification.Name("NNSongFavoriteStatusDidChangeNotification")
}

or

extension UIColor {
    @nonobjc static let superGiantRed = UIColor(red: 180.0/255.0, green: 40.0/255.0, blue: 27.0/255.0, alpha: 1.0)
}

Google Analytics pod

In Build Settings -> Other Linker Flags if you have the -ObjC on -l"GoogleAnalytics" flag this warning will appear. I don`t know why or how to resolve, but can be your problem too.

In my case it was a class variable.

public extension NSObject {
    public class var nameOfClass: String{
        return NSStringFromClass(self).components(separatedBy: ".").last!
    }

Adding @nonobjc helped.

For me the issue was that I was using a third-party framework from a vendor built with Xcode 7 in my Swift 3 application built with Xcode 8. Because the framework was a compiled binary, the only option I had was to ask my vendor for a new framework built with the latest version of Xcode.

I was able to solve my problem when I changed the "class var" to "class func":

There was:

class var applicationVersionNumber: String {
    if let version = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String {
        return version
    }
    return "Version Number Not Available"
}

Has become:

class func applicationVersionNumber() -> String {
    if let version = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String {
        return version
    }
    return "Version Number Not Available"
}

Source: https://forums.developer.apple.com/message/146579#146579

Rather than marking each member as @nonobjc individually, you can instead mark the entire extension as @nonobjc:

@nonobjc extension UIStoryboard {
  static let main = UIStoryboard(name: "Main", bundle: nil)
  static let welcome = UIStoryboard(name: "Main", bundle: nil)
}