ChatViewController.swift

class ChatViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, UITextFieldDelegate {
    
    @IBOutlet weak var tableView: UITableView!
    @IBOutlet weak var textField: UITextField!
    
    weak var agoraRtm: AgoraRtmKit?
    var channelName: String?
    var channel: AgoraRtmChannel?
    
    var handle: AuthStateDidChangeListenerHandle?
    var currentUser: User?
    
    var messageList: [String] = []
    
    override func viewWillAppear(_ animated: Bool) {
        handle = Auth.auth().addStateDidChangeListener { (auth, user) in
            self.currentUser = user
            if user != nil, let channelName = self.channelName {
                self.channel = self.agoraRtm?.createChannel(withId: channelName, delegate: self)
                self.channel?.join(completion: { (error) in
                    if error != .channelErrorOk {
                        print("Error joining channel: ", error.rawValue)
                    }
                })
            } else {
                DispatchQueue.main.async {
                    self.dismiss(animated: true, completion: nil)
                }
            }
        }
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        if let handle = handle {
            Auth.auth().removeStateDidChangeListener(handle)
        }
        if let channel = self.channel {
            channel.leave(completion: nil)
        }
    }
}