UITextField でキーボードの代わりに UIPickerView を表示

UIViewControllerWithPickerView.swift

class TestViewController: UIViewController {
    private var pickerView: UIPickerView!
    private var pickerViewToolbar: UIToolbar!
    private var pickerViewSelectedRow: Int?
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        self.setupPickerView()
        self.setupPickerViewToolbar()
        self.setupTextFieldWithPickerView(self.powerField)
    }
}

extension TestViewController {
    func pickerCancel() {
        self.view.endEditing(true)
    }
    
    func pickerDone() {
        //TODO: 選択された値を外部に反映
        self.view.endEditing(true)
    }
    
    private func setupPickerView() {
        self.pickerView = UIPickerView()
        self.pickerView.dataSource = self
        self.pickerView.delegate = self
    }

    private func setupPickerViewToolbar() {
        self.pickerViewToolbar = UIToolbar(frame: CGRectMake(0, 0, 0, 35))
        let done = UIBarButtonItem(barButtonSystemItem: .Done, target: self, action: #selector(TestViewController.pickerDone))
        let space = UIBarButtonItem(barButtonSystemItem: .FlexibleSpace, target: nil, action: nil)
        let cancel = UIBarButtonItem(barButtonSystemItem: .Cancel, target: self, action: #selector(TestViewController.pickerCancel))
        self.pickerViewToolbar.setItems([cancel, space, done], animated: true)
    }
    
    private func setupTextFieldWithPickerView(target: UITextField) {
        target.inputView = self.pickerView
        target.inputAccessoryView = self.pickerViewToolbar
        target.delegate = self
    }
}

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

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

extension TestViewController: UIPickerViewDelegate {
    func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        self.pickerViewSelectedRow = row
    }
}

extension TestViewController: UITextFieldDelegate {
    func textFieldShouldBeginEditing(textField: UITextField) -> Bool {
        // TextField 選択時に UIPickerView の選択値を変更する
        self.pickerView.selectRow(self.pickerViewSelectedRow ?? 0, inComponent: 0, animated: true)
        return true
    }
}