Display an alert using storyboard and custom UITabBarController-CodePudding

I am dealing with a problem using UITabBarController. I have a small project using storyboards (XCode 13, IOS 15 as base system). I created a TabBarController but I later discovered I could not manage it effectively programmatically. Reading various docs, I discovered I could use two scenes from my storyboard and creating the tabbar programmatically. So I did this in SceneDelegate.swift:

let queryViewControllerTab = storyBoard.instantiateViewController(withIdentifier: "QueryViewController")    
let settingsViewControllerTab = storyBoard.instantiateViewController(withIdentifier: "SettingsViewController")
let starredViewControllerTab = storyBoard.instantiateViewController(withIdentifier: "StarredViewController")
starredViewControllerTab.tabBarItem.title = "Starred"
starredViewControllerTab.tabBarItem.image = UIImage(systemName: "star")
// TODO: Discover why first two views keep reading image I setup previously in storyboard

let tabBarController = UITabBarController()
tabBarController.viewControllers = [queryViewControllerTab, settingsViewControllerTab, starredViewControllerTab]
tabBarController.selectedViewController = settingsViewControllerTab

self.window?.rootViewController = tabBarController
self.window?.makeKeyAndVisible()

This works perfectly and I can easily put a condition whether userDefaults are not set, load directly the settings.

In my class SettingsViewController I want to add an action where, upon pressing the button, you get an alert:

@IBAction func saveButtonPressed(_ sender: UIButton) {
        //        keychain.set(tokenInput.text ?? "", forKey: keychainKey)
        let alert = UIAlertController(title: "My Alert", message: "This is an alert.", preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: NSLocalizedString("OK", comment: "Default action"), 
                style: .default, handler: { _ in
        NSLog("The \"OK\" alert occured.")
        }))
        tabBarController.present(alert, animated: true, completion: nil)
}

But this makes the app crashing with unrecognized selector sent to instance 0x7f82f9705c30'

I've tried to debug the problem, and I understood I can't make the alert in this way because the view is really the tabBar and not the my scene. But here I got stuck. I tried to implement the UITabBarControllerDelegate, in StarredViewController, but I can't get it working.

extension StarredViewController: UITabBarControllerDelegate {
    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        print("did select tab bar item!")
    }
}

I start thinking my main setup with SceneDelegate and AppDelegate is wrong. Most of previous tutorials or threads I've found seems to fail even to compile because using deprecated versions.

CodePudding user response：

This is a way to present an alert from any presented View Controller.

Add some extensions:

import UIKit

extension UIViewController {
    var customVisibleViewController: UIViewController? {
        if let navigationController = self as? UINavigationController {
            return navigationController.topViewController?.customVisibleViewController
        } else if let tabBarController = self as? UITabBarController {
            return tabBarController.selectedViewController?.customVisibleViewController
        } else if let presentedViewController = presentedViewController {
            return presentedViewController.customVisibleViewController
        } else if self is UIAlertController {
            return nil
        } else {
            return self
        }
    }
}

extension UIApplication {
    /// The top most view controller
    static var topMostViewController: UIViewController? {
        return UIApplication.shared.keyWindow?.rootViewController?.customVisibleViewController
    }
}

Now you can show your alert in this way:

let alert = UIAlertController(title: "My Alert", message: "This is an alert.", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: NSLocalizedString("OK", comment: "Default action"), 
            style: .default, handler: { _ in
NSLog("The \"OK\" alert occured.")
}))
UIApplication.topMostViewController?.present(alert, animated: true, completion: nil)

CodePudding user response：

This is the code to trigger an alert. With addAction, you can add possible answers.

do {
    try //some method call or something else
} catch {
    let alert = UIAlertController(title: "There was an error while saving!", message: "Please try again", preferredStyle: .alert)
    alert.addAction(UIAlertAction(title: "I understand", style: .cancel, handler: nil))
}

you can find more information here: how to show an alert