Building the call interface

To be able to call, you will need to create a new View Controller for the calling interface. From the Xcode menu, select File > New > File.... Choose a Cocoa Touch Class, name it CallViewController with a subclass of UIViewController and language of Swift.

Xcode adding file
Xcode adding file

This will create a new file called CallViewController, at the top import NexmoClient.

import UIKit
import NexmoClient

The call interface will need:

  • A UIButton to start a call
  • A UIButton to end a call
  • A UILabel to show status updates

Open CallViewController.swift and add it programmatically.

class CallViewController: UIViewController {

    let callButton = UIButton(type: .system)
    let hangUpButton = UIButton(type: .system)
    let statusLabel = UILabel()

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")

    override func viewDidLoad() {
        view.backgroundColor = .systemBackground

        callButton.translatesAutoresizingMaskIntoConstraints = false

        hangUpButton.setTitle("Hang up", for: .normal)
        hangUpButton.translatesAutoresizingMaskIntoConstraints = false


        setStatusLabelText("Ready to receive call...")
        statusLabel.textAlignment = .center
        statusLabel.translatesAutoresizingMaskIntoConstraints = false

            callButton.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            callButton.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            callButton.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 20),
            callButton.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -20),

            hangUpButton.topAnchor.constraint(equalTo: callButton.bottomAnchor, constant: 20),
            hangUpButton.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            hangUpButton.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 20),
            hangUpButton.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -20),

            statusLabel.topAnchor.constraint(equalTo: hangUpButton.bottomAnchor, constant: 20),
            statusLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            statusLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 20),
            statusLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -20)

    private func setHangUpButtonHidden(_ isHidden: Bool) {
        DispatchQueue.main.async { [weak self] in
            guard let self = self else { return }
            self.hangUpButton.isHidden = isHidden
            self.callButton.isHidden = !self.hangUpButton.isHidden

    private func setStatusLabelText(_ text: String?) {
        DispatchQueue.main.async { [weak self] in
            guard let self = self else { return }
            self.statusLabel.text = text

There are two helper functions setHangUpButtonHidden and setStatusLabelText to avoid repetition of calling DispatchQueue.main.async as changing the state of the UI elements needs to be done on the main thread as required by UIKit. The setHangUpButtonHidden function toggles the visibility of the hangUpButton as this only needs to be visible during an active call.

Presenting the CallViewController

Now that the calling interface is built you will need to present the view controller from the log in screen you built earlier. You will need information about the logged in user to be passed between the two view controllers, within CallViewController.swift add the following.

class CallViewController: UIViewController {
    let user: User
    let client = NXMClient.shared
    let nc = NotificationCenter.default

    var call: NXMCall?

    init(user: User) {
        self.user = user
        super.init(nibName: nil, bundle: nil)

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")

This defines a custom initializer for the class which has a User.type as its parameter, which then gets stored in the local user property. Now that you have the user information you can use the callButton to show who the user will be calling, in viewDidLoad add the following.

navigationItem.leftBarButtonItem = 
UIBarButtonItem(title: "Logout", style: .done, target: self, action: #selector(self.logout))
callButton.setTitle("Call \(user.callPartnerName)", for: .normal)

It sets the title of the view controller and creates a logout button in the navigation bar. Add the corresponding logout function to the end of CallViewController.swift

class CallViewController: UIViewController {

     @objc func logout() {
        dismiss(animated: true, completion: nil)

Now you are ready to present the calling interface along with the user information. To do this you will need to edit the NXMClientDelegate extension in the ViewController.swift file.

extension ViewController: NXMClientDelegate {
    func client(_ client: NXMClient, didChange status: NXMConnectionStatus, reason: NXMConnectionStatusReason) {
        guard let user = self.user else { return }

        switch status {
        case .connected:
            self.statusLabel.text = "Connected"
            let navigationController = UINavigationController(rootViewController: CallViewController(user: user))
            navigationController.modalPresentationStyle = .overFullScreen
            self.present(navigationController, animated: true, completion: nil)

If the user connects successfully a CallViewController will be presented with the user data needed.

Build and Run

Run the project again (Cmd + R) to launch it in the simulator. If you log in with one of the users you will see the calling interface

Call interface
Call interface