Use this code to show an alert to the user when there is no internet connection. SWIFT IOS code

import SystemConfiguration

override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        if isInternetAvailable() {
            observeUsers()
        } else {
            let alert = UIAlertController(title: "No Connection", message: "No internet connection, connect to the internet and try again.", preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "ok", style: .default, handler: nil))
            present(alert, animated: true, completion: nil)
            
            return
        }
        
    }



  func isInternetAvailable() -> Bool {
        var zeroAddress = sockaddr_in()
        zeroAddress.sin_len = UInt8(MemoryLayout.size(ofValue: zeroAddress))
        zeroAddress.sin_family = sa_family_t(AF_INET)
        
        let defaultRouteReachability = withUnsafePointer(to: &zeroAddress) {
            $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {zeroSockAddress in
                SCNetworkReachabilityCreateWithAddress(nil, zeroSockAddress)
            }
        }
        
        var flags = SCNetworkReachabilityFlags()
        if !SCNetworkReachabilityGetFlags(defaultRouteReachability!, &flags) {
            return false
        }
        let isReachable = flags.contains(.reachable)
        let needsConnection = flags.contains(.connectionRequired)
        return (isReachable && !needsConnection)
    }