How do I call a function when UINavigationController UINavigationTabBar Item is tapped? - swift

Question

I want to be able to present a UIAlertAction when the user taps a UINavigationController UINavigationTabBar Item to remind them they need to enter some information before they can proceed to the next UIViewController that would otherwise be called from such a tap. The code that is called from the tap would check if an array is empty, if so, then display the UIAlertAction.
I've tried to create an instance of the UINavigationController's UINavigationTabBar item, to try and detect it being pushed, but this is messy as the UIViewController to be called has already been setup as a segue when the UINavigationTabBar item is tapped.
Do I need to backtrack and remove the existing segue and create the transition in a different way that allows my desired array checking code to be callable on the user's tap?

Answer 1

If you're pushing the next view controller using a segue, you would intercept that segue, do all your checks, and then inform the segue whether to go on or cancel the pushing. Basically in your view controller:
override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
if identifier == "NextViewControllerID" {
var isValid = true
// example of validation, do your stuff here
if myTextField.text?.count ?? 0 < 5 {
isValid = false
}
return isValid
}
// otherwise delegates the superclass
return super.shouldPerformSegue(withIdentifier: identifier, sender: sender)
}

Answer 2

import UIKit
class WordsViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
#IBOutlet weak var tableView: UITableView!
// write button selector method to check if there are any words.
var words = [String]()
var languages = [String]()
var chosenLanguage = String()
var textField: UITextField?
let wordString = "Words"
override func viewDidLoad() {
super.viewDidLoad()
chosenLanguageLoad()
loadInitialValues()
//let titleAttributes = [NSAttributedString.Key.font: UIFont(name: "AmericanTypewriter", size: 22)!]
//navigationController?.navigationBar.titleTextAttributes = titleAttributes
navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .play, target: self, action: #selector(test))
navigationItem.leftBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(addNewWord))
print("languages array is: \(languages)")
}
override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
if identifier == "Words" {
print("inside identifier == words if")
var isValid = true
if languages.isEmpty == true {
print("languages is empty is true")
isValid = false
}
return isValid
}
// otherwise delegates the superclass
return super.shouldPerformSegue(withIdentifier: identifier, sender: sender)
}
#objc func test() {
if words.isEmpty == true {
let ac = UIAlertController(title: "Add Some Words", message: nil, preferredStyle: .alert)
let okAction = UIAlertAction(title: "OK", style: .default)
ac.addAction(okAction)
present(ac, animated: true)
} else {
self.performSegue(withIdentifier: "Test", sender: self)
}
}
func chosenLanguageLoad() {
if let defaults = UserDefaults(suiteName: "group.co.uk.tirnaelectronics.polyglot") {
if let loadChosenLanguage = defaults.object(forKey: "languageChosen") as? String {
chosenLanguage = loadChosenLanguage
print("Chosen language is: \(chosenLanguage)")
}
}
}
#objc func loadInitialValues() {
if let defaults = UserDefaults(suiteName: "group.co.uk.tirnaelectronics.polyglot") {
words.removeAll()
tableView.reloadData()
print("Words array after clear all: \(words)")
print("chosenLanguage in loadInitialValues: \(chosenLanguage)")
print("\(chosenLanguage)\(wordString)")
if var savedWords = defaults.object(forKey: "\(chosenLanguage)\(wordString)") as? [String] {
print("savedWords array is: \(savedWords)")
words = savedWords
savedWords.removeAll()
print("savedWords array after clear all: \(savedWords)")
} else {
saveInitialWordValues(to: defaults)
}
print("Words is : \(words)")
print("Number of words: \(words.count)")
tableView.reloadData()
}
}
func saveInitialWordValues(to defaults: UserDefaults) {
switch chosenLanguage {
case "german":
words.append("Bear::Baissespekulant::0")
words.append("Camel::Kamel::0")
words.append("Cow::Rind::0")
words.append("Fox::Fuchs::0")
words.append("Goat::Geiß::0")
words.append("Monkey::Affe::0")
words.append("Pig::Schwein::0")
words.append("Rabbit::Karnickel::0")
words.append("Sheep::Schaf::0")
//words.append("::")
print(words)
defaults.set(words, forKey: "germanWords")
print("At end of saveInitialGermanValues")
case "french":
words.append("Bear::l'ours::0")
words.append("Camel::le chameau::0")
words.append("Cow::la vache::0")
words.append("Fox::le renard::0")
words.append("Goat::la chèvre::0")
words.append("Monkey::le singe::0")
words.append("Pig::le cochon::0")
words.append("Rabbit::le lapin::0")
words.append("Sheep::le mouton::0")
//words.append("::")
print(words)
defaults.set(words, forKey: "frenchWords")
print("At end of saveInitialFrenchValues")
default:
break
}
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
chosenLanguageLoad()
loadInitialValues()
}
override func viewDidAppear(_ animated: Bool) {
navigationController?.setToolbarHidden(true, animated: false)
super.viewDidAppear(animated)
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
}
#objc func addNewWord() {
// create our alert controller
let ac = UIAlertController(title: "Add new word", message: nil, preferredStyle: .alert)
// add two text fields, one for English and one for French or German.
ac.addTextField { textField in
textField.placeholder = "English"
}
ac.addTextField { (textField) in
textField.placeholder = "\(self.chosenLanguage.capitalized)"
}
// create an "Add Word" button that submits the user's input
let submitAction = UIAlertAction(title: "Add Word", style: .default) { [unowned self, ac] (action: UIAlertAction!) in
// pull out the English and French words, or an empty string if there was a problem
let firstWord = ac.textFields?[0].text ?? ""
let secondWord = ac.textFields?[1].text ?? ""
let zeroTimesWrong = "0"
// submit the English and French word to the insertFlashcard() method
self.insertFlashcard(first: firstWord, second: secondWord, third: zeroTimesWrong)
}
// add the submit action, plus a cancel button
ac.addAction(submitAction)
ac.addAction(UIAlertAction(title: "Cancel", style: .cancel))
// present the alert controller to the user
present(ac, animated: true)
}
func insertFlashcard(first: String, second: String, third: String) {
guard first.count > 0 && second.count > 0 else { return }
let newIndexPath = IndexPath(row: words.count, section: 0)
words.append("\(first)::\(second)::\(third)")
tableView.insertRows(at: [newIndexPath], with: .automatic)
saveWords()
}
func tableView(_ tableView: UITableView, editActionsForRowAt indexPath: IndexPath) -> [UITableViewRowAction]? {
let delete = UITableViewRowAction(style: .default, title: "Delete") { action, indexPath in
self.words.remove(at: indexPath.row)
tableView.beginUpdates()
tableView.deleteRows(at: [indexPath], with: .left)
tableView.endUpdates()
// delete item at indexPath
}
let edit = UITableViewRowAction(style: .normal, title: "Edit") { (action, indexPath) in
let ac = UIAlertController(title: "Edit word", message: nil, preferredStyle: .alert)
// add two text fields, one for English and one for French
ac.addTextField { textField in
let word = self.words[indexPath.row]
let split = word.components(separatedBy: "::")
let englishWord = split[0]
textField.placeholder = "\(englishWord)"
}
ac.addTextField { (textField) in
let word = self.words[indexPath.row]
let split = word.components(separatedBy: "::")
let foreignWord = split[1]
textField.placeholder = "\(foreignWord)"
}
// create an "Add Word" button that submits the user's input
let submitAction = UIAlertAction(title: "Edit Word", style: .default) { [unowned self, ac] (action: UIAlertAction!) in
// pull out the English and French words, or an empty string if there was a problem
let firstWord = ac.textFields?[0].text ?? ""
let secondWord = ac.textFields?[1].text ?? ""
guard firstWord.count > 0 && secondWord.count > 0 else { return }
// edit item at indexPath
self.words.remove(at: indexPath.row)
self.words.insert("\(firstWord)::\(secondWord)", at: indexPath.row)
tableView.beginUpdates()
tableView.deleteRows(at: [indexPath], with: .automatic)
tableView.insertRows(at: [indexPath], with: .automatic)
tableView.endUpdates()
self.saveWords()
}
// add the submit action, plus a cancel button
ac.addAction(submitAction)
ac.addAction(UIAlertAction(title: "Cancel", style: .cancel))
// present the alert controller to the user
self.present(ac, animated: true)
}
edit.backgroundColor = UIColor.blue
return [delete, edit]
}
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return words.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
//print("In cellForRowAt function")
let cell = tableView.dequeueReusableCell(withIdentifier: "Word", for: indexPath)
let word = words[indexPath.row]
if word != "::" {
let split = word.components(separatedBy: "::")
print(split[0])
cell.textLabel?.text = split[0]
cell.detailTextLabel?.text = ""
//print(cell)
}
return cell
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
tableView.deselectRow(at: indexPath, animated: true)
if let cell = tableView.cellForRow(at: indexPath) {
if cell.detailTextLabel?.text == "" {
let word = words[indexPath.row]
let split = word.components(separatedBy: "::")
cell.detailTextLabel?.text = split[1]
} else {
cell.detailTextLabel?.text = ""
}
}
}
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
words.remove(at: indexPath.row)
tableView.deleteRows(at: [indexPath], with: .automatic)
saveWords()
}
func saveWords() {
if let defaults = UserDefaults(suiteName: "group.co.uk.tirnaelectronics.polyglot") {
defaults.set(words, forKey: "\(chosenLanguage)\(wordString)")
}
}
}