swfit 4 的新特性
今天编译代码发现了这个问题，查了下，修正很简单在相关类前加：
@objcMembers
class JKWLoginVC: UIViewController
{
}
或者在方法名前做修改
@objc func clickLoginBtn() {
}
As of Swift 4 you’ll start seeing the error “Argument of ‘#selector’ refers to instance method ‘firstPage()’ that is not exposed to Objective-C”,along with the proposed fix of “Add ‘@objc’ to expose this instance method to Objective-C”. What this means is that the Swift method in question isn’t visible to Objective-C,which matters because UIBarButtonItem is Objective-C code.
While adding @objc to individual methods is a working solution,I expect most people will just shrug their shoulders and put @objcMembers before their class – that automatically exposes everything in the class to Objective-C,just like Swift 3 used to. So,modify the class definition to this:
