我希望能够在用户点击UINavigationController UINavigationTabBar Item时显示UIAlertAction，以提醒他们在进入下一个UIViewController之前需要输入一些信息，否则可能会从这样的点击中调用它。从抽头调用的代码将检查数组是否为空，如果为空，则显示UIAlertAction。
我已经尝试创建UINavigationController的UINavigationTabBar项目的实例，以尝试检测它是否被推送，但这很麻烦，因为在点击UINavigationTabBar项时已将要调用的UIViewController设置为segue。 / p>
我是否需要回溯并删除现有的序列，并以不同的方式创建过渡，从而可以在用户点击时调用所需的阵列检查代码？
答案 0 :(得分：0)
如果要使用segue推送下一个视图控制器，则将拦截该segue，进行所有检查，然后通知segue是继续进行还是取消推送。基本上在您的视图控制器中：
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)
}
答案 1 :(得分：0)
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)")
}
}
}