是否可以在 Swift 中为特定的 iOS 版本定义一个变量？ 在班级

Question

Is it possible to achieve this on the Class level of an object? Specifically looking at this to have an app containing WatchConnectivity but also suppporting iOS8

class Test {
    if #available(iOS 9, *) {
        let session: WCSession ......
    }
}

Answer 1

You can use a computed static property:

public class Example {  
  public static var answerToEverything: Int {
    if #available(iOS 9, *) {
      return 42
    } else {
      return 0
    }
  }
}

Or, you can consider using @available attribute instead:

public class Example {
  @available(iOS, introduced=1.0)
  public static var answerToEverything: Int = 42
}

where 1.0 is the version of your library (not iOS).

This would be useful if you're more concerned about making sure it's used on iOS and less concerned about the iOS version.

Answer 2

You can wrap it with a computed property , for instance for UIMenu :

@available(iOS 13.0, *)
var menu: UIMenu? { // use this as a getter for what you want
   return _menu as? UIMenu
}
var _menu: Any? // use this reference as a setter for what you want