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How to use UIPickerView

Paul Hudson       @twostraws

The spinning, barrel-shaped picker view has been a hallmark component of iOS since the first iPhone, and it doesn’t take much work for you to use in your own apps.

First, create and position a UIPickerView where you want it. This code creates one at the bottom of the screen:

let picker = UIPickerView()
picker.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(picker)

picker.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor).isActive = true
picker.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor).isActive = true
picker.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true

Now decide what should be the data source and delegate for the picker view. Traditionally these are there to provide data (the data source) and respond to actions (the delegate), but UIPickerView gets these two confused so you really need both.

To make things easy here we’re going to use your existing view controller for both data source and delegate, but you should move this code elsewhere in your own projects.

First, add both UIPickerViewDataSource and UIPickerViewDelegate to the conformance list for your view controller:

class ViewController: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate {

Finally, implement three methods: numberOfComponents() describes how many individual segments there are in the picker view, numberOfRowsInComponent describes how many rows each segment has, and titleForRow provides the title for each row in each segment.

Here’s some example code to get you started:

func numberOfComponents(in pickerView: UIPickerView) -> Int {
    return 2
}

func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
    if component == 0 {
        return 10
    } else {
        return 100
    }
}

func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
    if component == 0 {
        return "First \(row)"
    } else {
        return "Second \(row)"
    }
}

Available from iOS 2.0

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