7.1. App 7

We will build the following app in this module.

Here,

• The first screen contains a button to fetch text from the second screen.

• If the user taps the button, it takes the user to the second screen.

• The second screen contains a TextField where a user can put some text. This screen also contains a button.

• If the user puts some text and taps the button, it returns to the first screen, and the user will see the text on the first screen.

• So, we have to send the text back to the first screen from the second screen. We will use the Notification Center to do that.

• The first screen will observe the text, and the second screen will post updates to the text.

Creating a new app, App7

Now, let's create a new app in Xcode and name it 'App7.' Add the views and controllers of two screens:

First Screen:

FirstScreenView.swift

//
//  FirstScreen.swift
//  App7
//
//  Created by Sakib Miazi on 5/22/23.
//

import UIKit

class FirstScreenView: UIView {
    var buttonFetch:UIButton!
    var labelReceivedText:UILabel!

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.backgroundColor = .white
        
        setupButtonFetch()
        setupLabelReceivedText()
        
        initConstraints()
    }
    
    //MARK: initializing UI elements...
    func setupButtonFetch(){
        buttonFetch = UIButton(type: .system)
        buttonFetch.setTitle("Fetch Text from Second Screen", for: .normal)
        buttonFetch.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(buttonFetch)
    }
    
    func setupLabelReceivedText(){
        labelReceivedText = UILabel()
        labelReceivedText.text = "Will receive text from Screen 2"
        labelReceivedText.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(labelReceivedText)
    }
    
    //MARK: setting up constraints...
    func initConstraints(){
        NSLayoutConstraint.activate([
            buttonFetch.topAnchor.constraint(equalTo: self.safeAreaLayoutGuide.topAnchor, constant: 32),
            buttonFetch.centerXAnchor.constraint(equalTo: self.safeAreaLayoutGuide.centerXAnchor),
            
            labelReceivedText.topAnchor.constraint(equalTo: buttonFetch.bottomAnchor, constant: 32),
            labelReceivedText.centerXAnchor.constraint(equalTo: self.safeAreaLayoutGuide.centerXAnchor),
        ])
    }
    
    //MARK: unused methods...
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
}

ViewController.swift

//
//  ViewController.swift
//  App7
//
//  Created by Sakib Miazi on 5/22/23.
//

import UIKit

class ViewController: UIViewController {

    let firstScreen = FirstScreenView()
    override func loadView() {
        view = firstScreen
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        title = "First Screen"
        
        //MARK: buttonSend target...
        firstScreen.buttonFetch
            .addTarget(self, action: #selector(onButtonFetchTapped), for: .touchUpInside)
        
    }
    
    @objc func onButtonFetchTapped(){
        let secondScrren = SecondScreenViewController()
        navigationController?.pushViewController(secondScrren, animated: true)
    }
}

Second Screen:

SecondScreenView.swift

//
//  SecondScreenView.swift
//  App7
//
//  Created by Sakib Miazi on 5/22/23.
//

import UIKit

class SecondScreenView: UIView {
    
    var labelInfo: UILabel!
    var textFieldSendBack: UITextField!
    var buttonSendBack: UIButton!

    override init(frame: CGRect) {
        super.init(frame: frame)
        
        self.backgroundColor = .white
        
        setupLabelInfo()
        setupTextFieldSendBack()
        setupButtonSendBack()
        
        initConstraints()
    }
    
    //MARK: setting up UI elements...
    func setupLabelInfo(){
        labelInfo = UILabel()
        labelInfo.text = "Type to send back:"
        labelInfo.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(labelInfo)
    }
    func setupTextFieldSendBack(){
        textFieldSendBack = UITextField()
        textFieldSendBack.placeholder = "Put text to send back to screen 1"
        textFieldSendBack.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(textFieldSendBack)
    }
    func setupButtonSendBack(){
        buttonSendBack = UIButton(type: .system)
        buttonSendBack.setTitle("Send Back", for: .normal)
        buttonSendBack.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(buttonSendBack)
    }
    
    //MARK: initializing constraints...
    func initConstraints(){
        NSLayoutConstraint.activate([
            labelInfo.topAnchor.constraint(equalTo: self.safeAreaLayoutGuide.topAnchor, constant: 32),
            labelInfo.centerXAnchor.constraint(equalTo: self.safeAreaLayoutGuide.centerXAnchor),
            
            textFieldSendBack.topAnchor.constraint(equalTo: labelInfo.bottomAnchor, constant: 16),
            textFieldSendBack.centerXAnchor.constraint(equalTo: self.safeAreaLayoutGuide.centerXAnchor),
            
            buttonSendBack.topAnchor.constraint(equalTo: textFieldSendBack.bottomAnchor, constant: 8),
            buttonSendBack.centerXAnchor.constraint(equalTo: self.safeAreaLayoutGuide.centerXAnchor),
        ])
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
}

SecondScreenViewController.swift

//
//  SecondScreenViewController.swift
//  App7
//
//  Created by Sakib Miazi on 5/22/23.
//

import UIKit

class SecondScreenViewController: UIViewController {
    let secondScreen = SecondScreenView()
    
    override func loadView() {
        view = secondScreen
    
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        title = "Second Screen"
        
        secondScreen.buttonSendBack
            .addTarget(self, action: #selector(onButtonSendBackTapped), for: .touchUpInside)
        
    }
    
    @objc func onButtonSendBackTapped(){
        if let text = secondScreen.textFieldSendBack.text{
            //Send text to First Screen...
        }else{
            //Alert invalid input...
        }
        
    }

}