Show UIPickerView like a keyboard, without UITextField

The cleanest way at least for me, and for Swift4 + Autolayout solution, without a UITextField is adding a UIView as a container of the UIPickerView and a UIToolbar for the top views/buttons.

Then toggle the inset/offset of that container view with animation if you want, to hide and unhide the picker.

PROPERTIES

private lazy var view_PickerContainer: UIView = {
    let view = UIView()
    view.backgroundColor = .white
    view.addSubview(self.timePicker)
    view.addSubview(self.toolbar_Picker)
    return view
}()

private lazy var timePicker: UIDatePicker = {
    let picker = UIDatePicker()
    picker.minimumDate = Date()
    picker.datePickerMode = .time
    picker.setDate(Date(), animated: true)
    return picker
}()

private let timeFormatter: DateFormatter = {
    let formatter = DateFormatter()
    formatter.dateFormat = "hh:mm a"
    return formatter
}()

private lazy var toolbar_Picker: UIToolbar = {
    let toolbar = UIToolbar()
    toolbar.barStyle = .blackTranslucent
    toolbar.barTintColor = .blueDarkText
    toolbar.tintColor = .white
    self.embedButtons(toolbar)
    return toolbar
}()

I use SnapKit to layout my views programmatically. You can use the timePicker's bounds.size as reference for your layout.

IMPLEMENTATION

In viewDidLoad()

    // Setup timepicker and its container.
    self.view.addSubview(self.view_PickerContainer)
    self.view_PickerContainer.snp.makeConstraints { (make) in
        make.height.equalTo(self.timePicker.bounds.size.height + 50.0)
        make.leading.trailing.equalToSuperview()
        self.constraint_PickerContainerBottom = make.bottom.equalToSuperview().inset(-500.0).constraint
    }

    self.timePicker.snp.makeConstraints { (make) in
        make.height.equalTo(self.timePicker.bounds.size.height)
        make.width.equalToSuperview()
        make.bottom.equalToSuperview()
    }

    // Add toolbar for buttons.
    self.toolbar_Picker.snp.makeConstraints { (make) in
        make.height.equalTo(40.0)
        make.top.leading.trailing.equalToSuperview()
    }

Embedding top views

private func embedButtons(_ toolbar: UIToolbar) {
    func setupLabelBarButtonItem() -> UIBarButtonItem {
        let label = UILabel()
        label.text = "Set Alarm Time"
        label.textColor = .white
        return UIBarButtonItem(customView: label)
    }

    let todayButton = UIBarButtonItem(title: "Today", style: .plain, target: self, action: #selector(self.todayPressed(_:)))

    let doneButton = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(self.donePressed(_:)))

    let flexButton = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: self, action: nil)

    toolbar.setItems([todayButton, flexButton, setupLabelBarButtonItem(), flexButton, doneButton], animated: true)
}

And the result looks like this:

I went with borisgolovnev's suggestion of an invisible UITextField and came up with the following Swift 2.3 implementation:

import UIKit

class PickerViewPresenter: UITextField {

    // MARK: - Initialization

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    init() {
        super.init(frame: CGRect.zero)
    inputView = pickerView
    inputAccessoryView = pickerInputAccessoryView
    }

    // MARK: - Public

    var pickerDelegate: UIPickerViewDelegate? {
        didSet {
            pickerView.delegate = pickerDelegate
        }
    }

    var pickerDataSource: UIPickerViewDataSource? {
        didSet {
            pickerView.dataSource = pickerDataSource
        }
    }

    var selectButtonAction: (() -> Void)?

    var currentlySelectedRow: Int {
        return pickerView.selectedRowInComponent(0)
    }

    func selectRowAtIndex(index: Int) {
        pickerView.selectRow(index, inComponent: 0, animated: false)
    }

    func showPicker() {
        self.becomeFirstResponder()
    }

    func hidePicker() {
        self.resignFirstResponder()
    }

    // MARK: - Views

    private let pickerView = UIPickerView(frame: CGRect.zero)

    private lazy var pickerInputAccessoryView: UIView = {
        let frame = CGRect(x: 0.0, y: 0.0, width: 0.0, height: 48.0)
        let pickerInputAccessoryView = UIView(frame: frame)

        // Customize the view here

        return pickerInputAccessoryView
    }()

    func selectButtonPressed(sender: UIButton) {
        selectButtonAction?()
    }

}

PickerViewPresenter can then conveniently be used as such:

class ViewController: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(pickerViewPresenter)
    }

    private let dataModel = [10, 20, 30, 40, 50]

    private lazy var pickerViewPresenter: PickerViewPresenter = {
        let pickerViewPresenter = PickerViewPresenter()
        pickerViewPresenter.pickerDelegate = self
        pickerViewPresenter.pickerDataSource = self
        pickerViewPresenter.selectButtonAction = { [weak self] () -> Void in
            guard let strongSelf = self else {
                return
            }
            let result = strongSelf.dataModel[pickerViewPresenter.currentlySelectedRow]
            pickerViewPresenter.hidePicker()
            // ...
        }

        return pickerViewPresenter
    }()

    private func presentPickerView {
        let index = 0 // [0..dataModel.count-1]
        pickerViewPresenter.selectRowAtIndex(index)
        pickerViewPresenter.showPicker()
    }

    // MARK: - UIPickerViewDataSource

    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {
        return 1
    }

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

    // MARK: - UIPickerViewDelegate

    func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return "\(dataModel[row]) drunken sailors"
    }

}

Hope someone finds this useful =)

Attach a UIPickerView as the inputView of a 0-sized UITextField that you have added to your view.

let picker = UIPickerView()
picker.dataSource = self
picker.delegate = self
        
let dummy = UITextField(frame: .zero)
view.addSubview(dummy)
        
dummy.inputView = picker
dummy.becomeFirstResponder()

A better option is still to use the UITextField. You don't have to actually show it on screen. Just put it in a 0x0 UIView so that it is not visible, set it's inputView to your UIPickerView and call becomeFirstResponder on it to show the picker and resignFirstResponder to hide it.

It is convenient to have a UIView subclass that implements all of that along with UIPickerViewDelegate and UIPickerViewDataSource methods.