iOS UIAlertController bold button changed in 8.3

From iOS 9 you can set the preferredAction value to the action which you want the button title to be bold.

    let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
    let OKAction = UIAlertAction(title: "OK", style: .Default, handler: nil)
    alert.addAction(cancelAction)
    alert.addAction(OKAction)
    alert.preferredAction = OKAction
    presentViewController(alert, animated: true) {}

The OK button which is on the right will be in bold font.

This is an intentional change to the SDK. I have just had a response from Apple to this radar on the issue, stating that:

This is an intentional change - the cancel button is to be bolded in alerts.

I can't find anything in the various change logs mentioning this, unfortunately.

So, we'll need to make changes to our apps in places to make some things make sense.

Since iOS 9, UIAlertController has a property called preferredAction. preferredAction has the following declaration:

var preferredAction: UIAlertAction? { get set }

The preferred action for the user to take from an alert. [...] The preferred action is relevant for the UIAlertController.Style.alert style only; it is not used by action sheets. When you specify a preferred action, the alert controller highlights the text of that action to give it emphasis. (If the alert also contains a cancel button, the preferred action receives the highlighting instead of the cancel button.) [...] The default value of this property is nil.

---

The Swift 5 / iOS 12 sample code below shows how to display a UIAlertController that will highlight the text of a specified UIAlertAction using preferredAction:

let alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)

let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
let okAction = UIAlertAction(title: "OK", style: .default, handler: { action in
    print("Hello")
})

alertController.addAction(cancelAction)
alertController.addAction(okAction)
alertController.preferredAction = okAction

present(alertController, animated: true, completion: nil)