Using NSObject for a UIViewDelegate instead of a UIViewController

Question

I have the following class that I want to use as my UIPickerViewDelegate

class TimePickerViewDelegate: NSObject, UIPickerViewDataSource, UIPickerViewDelegate  {

    let pickerData = ["Mozzarella","Gorgonzola","Provolone","Brie","Maytag Blue","Sharp Cheddar","Monterrey Jack","Stilton","Gouda","Goat Cheese", "Asiago"]

    //MARK: - Delegates and data sources
    //MARK: Data Sources
    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {
        return 1
    }
    func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return pickerData.count
    }

    //MARK: Delegates
    func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String! {
        return pickerData[row]
    }

    func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        println( pickerData[row] )
    }
}

I'm initializing it in my main UIViewController with the following

 override func viewDidLoad() {
    super.viewDidLoad()

    let timePickerViewDelegate = TimePickerViewDelegate()

    timePickerView.dataSource = timePickerViewDelegate
    timePickerView.delegate = timePickerViewDelegate
}

However, when I execute the app, I get the following error.

2014-11-30 15:49:22.046 HausClock[78601:10273448] -[NSISEngine numberOfComponentsInPickerView:]: unrecognized selector sent to instance 0x7da406e0
2014-11-30 15:49:22.052 HausClock[78601:10273448] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSISEngine numberOfComponentsInPickerView:]: unrecognized selector sent to instance 0x7da406e0'

It seems to be telling me that my TimePicker View can't respond to the appropriate selector, but if I move the delegate from the NSObject to the UIViewController and copy/paste the delegate functions, it works correctly.

Answer 1

dataSource and delegate are weak properties, you should declare timePickerViewDelegate as an instance property to hold a strong reference to the delegate.

let timePickerViewDelegate = TimePickerViewDelegate()

override func viewDidLoad() {
    super.viewDidLoad()

    timePickerView.dataSource = timePickerViewDelegate
    timePickerView.delegate = timePickerViewDelegate
}