How do I use multiple picker views with different data sources in the same view?

Question

I have a view with three picker views in it. Two of the picker views have the same data, an array with the numbers 1 to 100. The third picker view has an array with a list

Answer 1

When dealing with multiple controls with delegates and data sources, you should consider avoiding view controller bloat (i.e., in the spirit of the single responsibility principle) by creating separate objects for the delegates of the multiple pickers. This keeps this logic out of the view controller, itself, and avoids single cumbersome UIPickerViewDataSource and UIPickerViewDelegate methods trying to service multiple pickers with hairy if-else or switch statements.

For example, here is a view controller that has outlets for two pickers, but rather than encumbering the view controller with code to manage the dataSource and delegate for these pickers, you can have separate objects for each picker, and all the view controller has to do is to say which delegate object will handle which picker:

class ViewController: UIViewController {

    @IBOutlet weak var namePicker: UIPickerView!
    @IBOutlet weak var numberPicker: UIPickerView!

    let namePickerDelegate = NamePickerDelegate()
    let numberPickerDelegate = NumberPickerDelegate()

    override func viewDidLoad() {
        super.viewDidLoad()

        namePicker.delegate = namePickerDelegate
        namePicker.dataSource = namePickerDelegate

        numberPicker.delegate = numberPickerDelegate
        numberPicker.dataSource = numberPickerDelegate
    }

    @IBAction func didTapButton(_ sender: Any) {
        let nameValue = namePicker.selectedRow(inComponent: 0)
        let numberValue = numberPicker.selectedRow(inComponent: 0)

        print("\(nameValue); \(numberValue)")
    }

}

The only trick is to make sure to keep a strong reference to those delegate objects, as shown above, because the picker, itself, only has weak references to its delegate, as is best practice.

And the implementation of the picker delegate methods is much cleaner:

class NamePickerDelegate: NSObject, UIPickerViewDataSource, UIPickerViewDelegate {
    let names = ["Mo", "Larry", "Curley"]

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return names.count
    }

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return names[row]
    }
}

class NumberPickerDelegate: NSObject, UIPickerViewDataSource, UIPickerViewDelegate {
    let numbers: [String] = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .spellOut
        return (0 ..< 100).compactMap { formatter.string(for: $0) }  // use `flatMap` in Xcode versions prior to 9.3
    }()

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return numbers.count
    }

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return numbers[row]
    }
}

Now, this is still, obviously, a simplified example, but the beauty is that as the code gets more complicated, the details are encapsulated within separate objects, rather than encumbering a single view controller with all the code.

---

If you want, you can have the view controller provide the list of strings to the delegate/data source object. In fact, that simplifies it because you need only one class for the picker delegate, and you just instantiate a different one for each picker:

class ViewController: UIViewController {

    let names = ["Mo", "Larry", "Curley"]

    let numbers: [String] = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .spellOut
        return (0 ..< 100).compactMap { formatter.string(for: $0) }  // use `flatMap` in Xcode versions prior to 9.3
    }()

    @IBOutlet weak var numberPickerOne: UIPickerView!
    @IBOutlet weak var numberPickerTwo: UIPickerView!
    @IBOutlet weak var namePicker: UIPickerView!

    lazy var numberPickerOneDelegate: PickerDelegate = PickerDelegate(strings: self.numbers)
    lazy var numberPickerTwoDelegate: PickerDelegate = PickerDelegate(strings: self.numbers)
    lazy var namePickerDelegate:PickerDelegate = PickerDelegate(strings: self.names)

    override func viewDidLoad() {
        super.viewDidLoad()

        numberPickerOne.delegate   = numberPickerOneDelegate
        numberPickerOne.dataSource = numberPickerOneDelegate

        numberPickerTwo.delegate   = numberPickerTwoDelegate
        numberPickerTwo.dataSource = numberPickerTwoDelegate

        namePicker.delegate        = namePickerDelegate
        namePicker.dataSource      = namePickerDelegate
    }

}

class PickerDelegate: NSObject, UIPickerViewDataSource, UIPickerViewDelegate {
    let strings: [String]

    init(strings: [String]) {
        self.strings = strings
        super.init()
    }

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return strings.count
    }

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return strings[row]
    }
}