Using a multi component picker in a SwiftUI form

SwiftUI has a Picker view available with multiple different styles. One example of when it falls short is when we want to use a multi component picker with wheel style. One way how to try to achieve this is using a HStack with two Picker views, but it does not work very well, especially when trying to show it inside a Form view. So what else we can do? If something can’t be done in SwiftUI then we can use UIKit instead.

In my case, I wanted to create a picker which allows picking a date duration. It would have one wheel for selecting a number and the other wheel for selecting either days, weeks or months.

Screenshot of a SwiftUI form with a two component wheel picker where left wheel selects a number and right wheel selects days, weeks or months.

Firstly, let’s create a tiny struct which is going to hold the state of this picker. It needs to store a numeric value and the unit: days, weeks, months. Let’s name it as DateDuration. Since we want to iterate over the DateDuration.Unit, we’ll conform it to CaseIterable protocol.

struct DateDuration {
let value: Int
let unit: Unit
enum Unit: String, CaseIterable {
case days, weeks, months
}
}

UIPickerView in UIKit can do everything we want, therefore we’ll need to wrap it into a SwiftUI view. This can be done by creating a new type which conforms to UIViewRepresentable protocol. Also, we need a binding which holds the value of the current selection: when the user changes it, the binding communicates the changes back and vice-versa. Additionally, we’ll add properties for configuring values and units. UIPickerView us created and configured in the makeUIView(context:) function. UIPickerView is driven by a data source and a delegate, which means we require a coordinator object as well. Coordinator is part of the UIViewRepresentable protocol.

struct DateDurationPicker: UIViewRepresentable {
let selection: Binding<DateDuration>
let values: [Int]
let units: [DateDuration.Unit]
func makeUIView(context: Context) -> UIPickerView {
let pickerView = UIPickerView(frame: .zero)
pickerView.translatesAutoresizingMaskIntoConstraints = false
pickerView.delegate = context.coordinator
pickerView.dataSource = context.coordinator
return pickerView
}
//
}

Coordinator is created in the makeCoordinator() function. It is going to do most of the work by providing data to the UIPickerView and handling the current selection. Therefore, we’ll store the selection binding, values, and units in the Coordinator class as well.

struct DateDurationPicker: UIViewRepresentable {
//
func makeCoordinator() -> Coordinator {
return Coordinator(selection: selection, values: values, units: units)
}
final class Coordinator: NSObject, UIPickerViewDataSource, UIPickerViewDelegate {
let selection: Binding<DateDuration>
let values: [Int]
let units: [DateDuration.Unit]
init(selection: Binding<DateDuration>, values: [Int], units: [DateDuration.Unit]) {
self.selection = selection
self.values = values
self.units = units
}
//
}
}

The last missing piece is implementing UIPickerViewDataSource and UIPickerViewDelegate methods in the Coordinator class. This is pretty straight-forward to do. We’ll need to display two components where the first component is the list of values and the second component is the unit: days, weeks, months. When the user selects a new value, we’ll change the DateDuration value of the binding.

func numberOfComponents(in pickerView: UIPickerView) -> Int {
return 2
}
func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
return component == 0 ? values.count : units.count
}
func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
if component == 0 {
return "\(values[row])"
}
else {
return units[row].rawValue
}
}
func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
let valueIndex = pickerView.selectedRow(inComponent: 0)
let unitIndex = pickerView.selectedRow(inComponent: 1)
selection.wrappedValue = DateDuration(value: values[valueIndex], unit: units[unitIndex])
}

Finally, let’s hook it up in an example view.

struct ContentView: View {
@StateObject var viewModel = ViewModel()
var body: some View {
NavigationView {
Form {
Section {
//
DateDurationPicker(
selection: $viewModel.selection,
values: Array(1..<100),
units: DateDuration.Unit.allCases
)
//
}
}
.navigationTitle("Reminders")
}
}
}
extension ContentView {
final class ViewModel: ObservableObject {
@Published var selection = DateDuration(value: 1, unit: .days)
//
}
}

Example Project

SwiftUIDateDurationPicker (GitHub, Xcode 13.2.1)

If this was helpful, please let me know on Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.