Changez automatiquement la taille de la police pour adapter le bouton Swift

J'ai essayé ceci mais cela n'a pas fonctionné, le texte est sorti des limites des boutons.

 func nextQuestion() {

    let currentQuestion = mcArray![questionIdx]

    answers = currentQuestion["Answers"] as! [String]
    correctAnswer = currentQuestion["CorrectAnswer"] as? String
    question = currentQuestion["Question"] as? String

    titlesForButtons()
}

func titlesForButtons() {
    for (idx,button) in answerButtons.enumerate() {
        button.titleLabel!.lineBreakMode = .ByWordWrapping

        button.titleLabel!.font = UIFont(name: "Heiti TC", size: 5)

        button.titleLabel!.numberOfLines = 0

        button.titleLabel!.minimumScaleFactor = 0.1

        button.titleLabel!.baselineAdjustment = .AlignCenters

        button.titleLabel!.textAlignment  = NSTextAlignment.Center

        button.setTitle(answers[idx], forState: .Normal)
        button.enabled = true
        button.backgroundColor = UIColor(red: 83.0/255.0, green: 184.0/255.0, blue: 224.0/255.0, alpha: 1.0)
    }

    questionLabel.text = question
    startTimer()
}