Alert that can work on iOS 7 and iOS 8

Question

I'm getting dyld: Symbol not found: _OBJC_CLASS_$_UIAlertAction when I'm trying to get this monstrosity to run.

How do I weaklink 8.0 stuff?

var device : UIDevice = UIDevice.currentDevice()!;
var systemVersion = device.systemVersion;
var iosVerion : Float = systemVersion.bridgeToObjectiveC().floatValue;
if(iosVerion < 8.0) {
    let alert = UIAlertView()
    alert.title = "Noop"
    alert.message = "Nothing to verify"
    alert.addButtonWithTitle("Click")
    alert.show()
} else {
    var alert : UIAlertController? = UIAlertController(title: "Noop", message: "Nothing to verify", preferredStyle: UIAlertControllerStyle.Alert)
    if alert {
        let actionStyle : UIAlertActionStyle? = UIAlertActionStyle.Default;
        var alertAction : UIAlertAction? = UIAlertAction(title: "Click", style: actionStyle!, handler: nil)
        if(alertAction) {
            alert!.addAction(alertAction)
            self.presentViewController(alert, animated: true, completion: nil)
        }
    }
}
return;

Resolved: UIKit had to be marked Optional rather than Required. Simplified version is now:

var device : UIDevice = UIDevice.currentDevice()!;
var systemVersion = device.systemVersion;
var iosVerion : Float = systemVersion.bridgeToObjectiveC().floatValue;
if(iosVerion < 8.0) {
    let alert = UIAlertView()
    alert.title = "Noop"
    alert.message = "Nothing to verify"
    alert.addButtonWithTitle("Click")
    alert.show()
} else {
    var alert : UIAlertController = UIAlertController(title: "Noop", message: "Nothing to verify", preferredStyle: UIAlertControllerStyle.Alert)
    alert.addAction(UIAlertAction(title: "Click", style:.Default, handler: nil))
    self.presentViewController(alert, animated: true, completion: nil)
}

Answer 1

• Explicitly add UIKit in the "Link Binary With Libraries" section of your project's build phases.

• You can test for the existence of UIAlertController like this:

  if NSClassFromString("UIAlertController") != nil {
      // Use it
  } else {
      // Fall back
  }
  

• I wrote a wrapper that works on both iOS 7 and iOS 8. You can find it here. It takes a view controller followed by a bunch of optional arguments and any number of buttons:

  showAlert(self, style: .ActionSheet, sourceView: cell, completion: {
      tableView.deselectRowAtIndexPath(indexPath, animated: true)
  },
      (.Default, "Send clipboard", {
          if someCondition {
              // completion must be specified because of a Swift bug (rdar://18041904)
              showAlert(self, title: "Nothing to send", message: "The clipboard is empty.", completion: nil,
                  (.Cancel, "OK", nil)
              )
          }
      }),
      (.Cancel, "Cancel", nil)
  )