Swift's didSet property observer is a great way to dynamically configure a view at runtime, but there are limits to what you should do with it. Read the blog post here: http://www.chibicode.org/?p=32

DidSetExample.swift

class MyClass {
    @IBOutlet weak var outputLabel: UILabel! {
        didSet {
            // Ensure that the label wasn't just set to nil.
            guard let outputLabel = self.outputLabel else { return }
            
            // Set the text color based on the user's style choices.
            outputLabel.textColor = StyleManager.sharedManager().outputLabelColor
            
            // Set the label to use fixed-width numbers.
            let oldDescriptor = outputLabel.font.fontDescriptor()
            let fontAttributes = [
                UIFontDescriptorFeatureSettingsAttribute : [
                    UIFontFeatureTypeIdentifierKey : kNumberSpacingType,
                    UIFontFeatureSelectorIdentifierKey : kMonospacedNumbersSelector
                ]
            ]
            let newDescriptor = oldDescriptor.fontDescriptorByAddingAttributes(fontAttributes)
            outputLabel.font = UIFont(descriptor: newDescriptor, size: 0)
        }
    }
}