Multi-Component Picker (UIPickerView) in SwiftUI

问题:

I'm trying to add a three-component Picker (UIPickerView) to a SwiftUI app (in a traditional UIKit app, the data source would return 3 from the numberOfComponents method), but I can't find an example of this anywhere.

I've tried adding an HStack of three single-component Pickers, but the perspective is off from what it would be if they were all part of a single Picker.

回答1:

The best solution I found - so far - is to port the original UIPickerView in SwiftUI, via UIViewRepresentable and a coordinator.

Porting UIKit components to SwiftUI is discussed in this amazing WWDC 2019 video:

Integrating SwiftUI

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Here's the result (see demo code at the bottom):

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Implementation:

There are two bindings, data and selection, that are passed down from the superview.

data is an array of array of Data, e.g.

[
  Array(1...100),
  Array(1...100),
  Array(1...100)
]

Each array represent a picker component.

Each value in an array represent a row in a picker component.

selection is an array of Data, e.g. [10, 20, 30]

It represents the picker selection (across all components).

If one of the bindings changes, it triggers a redraw of all components.

Also, the selection is restored.

struct CustomPicker<Data>: UIViewRepresentable where Data: Equatable {

    @Binding var data: [[Data]]
    @Binding var selection: [Data]

    class Coordinator: NSObject, UIPickerViewDelegate, UIPickerViewDataSource {

        @Binding var data: [[Data]]
        @Binding var selection: [Data]

        init(data: Binding<[[Data]]>, selection: Binding<[Data]>) {
            $data = data
            $selection = selection
        }

        func pickerView(_ pickerView: UIPickerView,
                        numberOfRowsInComponent component: Int) -> Int {
            data[component].count
        }

        func numberOfComponents(in pickerView: UIPickerView) -> Int {
            data.count
        }

        func pickerView(_ pickerView: UIPickerView,
                        widthForComponent component: Int) -> CGFloat {
            return (pickerView.superview?.bounds.width ?? 0) * 0.33
        }

        func pickerView(_ pickerView: UIPickerView,
                        rowHeightForComponent component: Int) -> CGFloat {
            return 30
        }

        func pickerView(_ pickerView: UIPickerView,
                        viewForRow row: Int,
                        forComponent component: Int,
                        reusing view: UIView?) -> UIView {
            guard let reusableView = view as? UILabel else {
                let label = UILabel(frame: .zero)
                label.backgroundColor = UIColor.red.withAlphaComponent(0.15)
                label.text = "\(data[component][row])"
                return label
            }
            reusableView.text = "\(data[component][row])"
            return reusableView
        }

        func pickerView(_ pickerView: UIPickerView,
                        didSelectRow row: Int,
                        inComponent component: Int) {
            let value = data[component][row]
            selection[component] = value
        }
    }

    func makeCoordinator() -> CustomPicker.Coordinator {
        return Coordinator(data: $data,
                           selection: $selection)
    }

    func makeUIView(context: UIViewRepresentableContext<CustomPicker>) -> UIPickerView {
        let picker = UIPickerView()
        picker.delegate = context.coordinator
        return picker
    }

    func updateUIView(_ uiView: UIPickerView,
                      context: UIViewRepresentableContext<CustomPicker>) {

        uiView.reloadAllComponents()
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
            self.selection.enumerated().forEach { tuple in
                let (offset, value) = tuple
                let row = self.data[offset].firstIndex { $0 == value } ?? 0
                uiView.selectRow(row, inComponent: offset, animated: false)
            }
        }

    }

}

---

Demo:

struct ContentView: View {

    @State var data: [[Int]] = [
        Array(0...10),
        Array(20...40),
        Array(100...200)
    ]
    @State var selection: [Int] = [0, 20, 100]

    var body: some View {
        NavigationView {
            VStack {
                CustomPicker(data: self.$data,
                             selection: self.$selection)
                Text("Selection: \(String(describing: selection))")
            }
        }
    }

}

回答2:

This isn't quite as elegant but it doesn't involve porting over any UIKit stuff. I know you mentioned perspective was off in your answer but perhaps the geometry here fixes that

GeometryReader { geometry in

    HStack
    {
         Picker(selection: self.$selection, label: Text(""))
         {
              ForEach(0 ..< self.data1.count)
              {
                  Text(self.data1[$0])
                     .color(Color.white)
                     .tag($0)
              }
          }
          .pickerStyle(.wheel)
          .fixedSize(horizontal: true, vertical: true)
          .frame(width: geometry.size.width / 2, height: geometry.size.height, alignment: .center)


          Picker(selection: self.$selection2, label: Text(""))
          {
               ForEach(0 ..< self.data2.count)
               {
                   Text(self.data2[$0])
                       .color(Color.white)
                       .tag($0)
               }
          }
          .pickerStyle(.wheel)
          .fixedSize(horizontal: true, vertical: true)
          .frame(width: geometry.size.width / 2, height: geometry.size.height, alignment: .center)

    }
}

Using the geometry and fixing the size like this shows the two pickers neatly taking up half the width of the screen in each half. Now you just need to handle selection from two different state variables instead of one but I prefer this way as it keeps everything in swift UI