触摸 UITextField 时设置 UIPickerView 的默认值

Question

I want to keep the same placeholder text in my UITextField which is "Location". Once the UITextField is touched then I want the first value of the UIPickerView to be displayed. The way it is now the user has to scroll down then back up for the value to be displayed in the UITextField. I want the value to be displayed in the UITextField as soon as the UIPickerView is open. unselected, selected-UITextField still shows no value

override func viewDidLoad() {
    let thePicker = UIPickerView()
    thePicker.delegate = self
    location.inputView = thePicker
    thePicker.selectRow(1, inComponent: 0, animated: true)
}

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

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

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


func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
    location.text = pickOptions[row]
}

Answer 1

Implement the textFieldDidBeginEditing text field delegate method and set the text field's text if it doesn't already have a value.

func textFieldDidBeginEditing(_ textField: UITextField) {
    if textField.text!.isEmpty {
        // set the text as needed
    }
}

Answer 2

I'm going to build on rmaddy's answer and add more nuances and answers to questions in the comments.

Main answer lays in the first extension, the rest of the code outlines class structure and components that need to be present for everything to work.

class ViewController {
    private var selectedItem: String = ""
    private let pickerList = [
        "First item",
        "Second item",
        "Third item"
    ]
     override func viewDidLoad() {
        super.viewDidLoad()
        pickerTextField.delegate = self
        //...
        // Layout setup
        //...
    }
    private let pickerTextField: UITextField = {
        let textField = UITextField()
        textField.tintColor = .clear // hides cursor
        return textField
    }()
    //...
    // UI Elements including picker
    //...
}

extension ViewController: UITextFieldDelegate {
    internal func textFieldDidBeginEditing(_ textField: UITextField) {
        if textField == pickerTextField, let textFieldText = textField.text, textFieldText.isEmpty {
            pickerTextField.text = pickerList.first   // fills textfield before any selection is made
        }
    }
}

extension ViewController: UIPickerViewDelegate, UIPickerViewDataSource {
    //...
    // PickerView delegate methods
    //...
}

Answer 3

import UIKit

class ActivityPersonDetail : UIViewController,UITextFieldDelegate,UIPickerViewDataSource, UIPickerViewDelegate {


    let salutations = ["1", "2", "3","4","5","6","7","8","9","10","11","12"]

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

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

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

    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        pickerTF.text = salutations[row]
        picker.isHidden = true

    }

    func textFieldDidBeginEditing(_ textField: UITextField) {

        if textField == self.pickerTF {
            picker.isHidden = false
            textField.endEditing(true)
        }
    }


    lazy var picker: UIPickerView = {
        let pickerView = UIPickerView()
        pickerView.delegate = self
        pickerView.translatesAutoresizingMaskIntoConstraints = false
        pickerView.backgroundColor = .white

        pickerTF.inputView = pickerView
        return pickerView
    }()

    let  arrowImage: UIImageView = {

        let image = UIImageView()
        image.translatesAutoresizingMaskIntoConstraints = false
        image.image = #imageLiteral(resourceName: "down_arrow")
        image.contentMode = .scaleAspectFit
        return image
    } ()

    lazy var pickerTF: UITextField = {

        let tf = UITextField()
        tf.delegate = self
        tf.translatesAutoresizingMaskIntoConstraints = false
        tf.textColor = .black
        tf.font = .systemFont(ofSize: 24, weight: .medium)
        tf.placeholder = salutations[0]
        return tf
    }()



    //
    // MARK :- viewDidLoad ============================================================================
    //
    private var pickerView: UIPickerView!

    override func viewDidLoad() {

        super .viewDidLoad()
        view.backgroundColor = .white

        setupNavigationBar()
        setupViews()
        setupAutoLayout()

    }

    // ================ setupNavigationBar =============

    func setupNavigationBar(){

        title = ""
        hideBackTitle()
        navigationController?.navigationBar.barTintColor = .navBar

    }
    func hideBackTitle() {
        let backbarItem = UIBarButtonItem()
        backbarItem.title = ""
        navigationItem.backBarButtonItem = backbarItem
    }


    // ================ setupViews =============

    func setupViews(){

        view.addSubview(pickerTF)
        pickerTF.addSubview(arrowImage)
        view.addSubview(picker)
        picker.isHidden = true
    }


    // ================ setupAutoLayout =============

    func setupAutoLayout() {

        pickerTF.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 80).isActive = true
        pickerTF.topAnchor.constraint(equalTo: view.topAnchor, constant: 80).isActive = true
        pickerTF.heightAnchor.constraint(equalToConstant: 60).isActive = true
        pickerTF.widthAnchor.constraint(equalToConstant: 70).isActive = true

        arrowImage.rightAnchor.constraint(equalTo: pickerTF.rightAnchor, constant: -15).isActive = true
        arrowImage.topAnchor.constraint(equalTo: pickerTF.topAnchor, constant: 16).isActive = true
        arrowImage.widthAnchor.constraint(equalToConstant: 22).isActive = true
        arrowImage.heightAnchor.constraint(equalToConstant: 22).isActive = true

        picker.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        picker.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        picker.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
        picker.heightAnchor.constraint(equalToConstant: 100).isActive = true


    }

}

Answer 4

@IBOutlet weak var tF: UITextField!

override func viewDidLoad() {
    super.viewDidLoad()

    tF.delegate = self
}

func textFieldDidEndEditing(_ textField: UITextField) {
    textField.text = pickOptions[row]
}