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)
  )
  

Answer 2

In Xcode 6 beta 5, there is nothing in Link Phases -> Link Binary With Libraries since Swift links frameworks implicitly. In this case you need to add it manually there and mark optional then.

Also instead of checking for system version explicitly you can just check for UIAlertController availability

if nil != NSClassFromString("UIAlertController") {
  //show alertcontroller
  ...
} else {
  //show alertview
  ...
}