Tag: UIViewRepresentable

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.

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
	}
	}

view raw DateDuration.swift hosted with ❤ by GitHub

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
	}
	// …
	}

view raw DateDurationPicker.swift hosted with ❤ by GitHub

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
	}
	// …
	}
	}

view raw DateDurationPicker.swift hosted with ❤ by GitHub

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])
	}

view raw DateDurationPicker.swift hosted with ❤ by GitHub

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)
	// …
	}
	}

view raw ContentView.swift hosted with ❤ by GitHub

Example Project

SwiftUIDateDurationPicker (GitHub, Xcode 13.2.1)

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