A SwiftUI field with a UIPickerView as a keyboard

ContentView.swift

import SwiftUI

struct ContentView: View {
    @State var selectedIndex: Int? = nil
    let options: [String] = ["Option1", "Option2"]

    var body: some View {
       PickerField("Select an option", data: self.options, selectionIndex: self.$selectedIndex)
    }
}

PickerField.swift

import SwiftUI

struct PickerField: UIViewRepresentable {
    // MARK: - Public properties
    @Binding var selectionIndex: Int?

    // MARK: - Initializers
    init<S>(_ title: S, data: [String], selectionIndex: Binding<Int?>) where S: StringProtocol {
        self.placeholder = String(title)
        self.data = data
        self._selectionIndex = selectionIndex

        textField = PickerTextField(data: data, selectionIndex: selectionIndex)
    }

    // MARK: - Public methods
    func makeUIView(context: UIViewRepresentableContext<PickerField>) -> UITextField {
        textField.placeholder = placeholder
        return textField
    }

    func updateUIView(_ uiView: UITextField, context: UIViewRepresentableContext<PickerField>) {
        if let index = selectionIndex {
            uiView.text = data[index]
        } else {
            uiView.text = ""
        }
    }

    // MARK: - Private properties
    private var placeholder: String
    private var data: [String]
    private let textField: PickerTextField
}

PickerTextField.swift

import SwiftUI

class PickerTextField: UITextField {
    // MARK: - Public properties
    var data: [String]
    @Binding var selectionIndex: Int?

    // MARK: - Initializers
    init(data: [String], selectionIndex: Binding<Int?>) {
        self.data = data
        self._selectionIndex = selectionIndex
        super.init(frame: .zero)

        self.inputView = pickerView
        self.tintColor = .clear
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // MARK: - Private properties
    private lazy var pickerView: UIPickerView = {
        let pickerView = UIPickerView()
        pickerView.delegate = self
        pickerView.dataSource = self
        return pickerView
    }()

    // MARK: - Private methods
    @objc
    private func donePressed() {
        self.selectionIndex = self.pickerView.selectedRow(inComponent: 0)
        self.endEditing(true)
    }
}

// MARK: - UIPickerViewDataSource & UIPickerViewDelegate extension
extension PickerTextField: UIPickerViewDataSource, UIPickerViewDelegate {
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }

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

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

    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        self.selectionIndex = row
    }
}

Hi guys, here's some thips.

You can add a done button with a tool bar using the code below in PickerTextField Class

init(data: [String], selectionIndex: Binding<Int?>) {
    let toolBar = UIToolbar()
    toolBar.barStyle = UIBarStyle.default
    toolBar.isTranslucent = true
    toolBar.sizeToFit()
        
    let doneButton = UIBarButtonItem(title: "Done", style: UIBarButtonItem.Style.done, target: self, action: #selector(self.donePressed))
    let spaceButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonItem.SystemItem.flexibleSpace, target: nil, action: nil)

    toolBar.setItems([spaceButton, doneButton], animated: false)
    toolBar.isUserInteractionEnabled = true

    self.inputAccessoryView = toolBar
}

@objc private func donePressed() {
    self.resignFirstResponder()
}

Also, you can make users can't copy and paste or drag the content inside of the text field with the code below
Just copy and paste inside of PickerTextField class.

override func canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool {
        false
}
    
override func selectionRects(for range: UITextRange) -> [UITextSelectionRect] {
    []
}

override func caretRect(for position: UITextPosition) -> CGRect {
    .zero
}

Good luck!

Thanks for your tips, @diamantidis

override func caretRect(for position: UITextPosition) -> CGRect {
.null
}

This will truly make it unselectable! Relevant StackOverflow post: https://stackoverflow.com/questions/32846678/how-to-disable-the-selection-of-a-uitextfield/62754240#62754240