func listenForFirebaseConnection(callback: @escaping () -> Void) {
    FireDataUtil().getBase().child(".info/connected").observeSingleEvent(of: .value, with: { (snapshot) in
            if snapshot.exists() {
                let isConnected = snapshot.value as! Bool?
                if isConnected != nil && isConnected == false {

                    let view = MessageView.viewFromNib(layout: .MessageView)
                    view.button?.isHidden = false

                    // Theme message elements with the warning style.
                    view.configureTheme(.error)

                    // Add a drop shadow.
                    view.configureDropShadow()

                    // Set message title, body, and icon. Here, we're overriding the default warning
                    // image with an emoji character.
                    view.configureContent(title: "Network Issue", body: "It looks like your network connection is either slow or disconnected")
                    view.button?.setTitle("Reload", for: .normal)

                    view.button?.addTarget(self, action: #selector(callback), for: .touchUpInside)
                    var config = SwiftMessages.Config()

                    config.presentationContext = .window(windowLevel: UIWindowLevelStatusBar)
                    config.presentationStyle = .bottom
                    config.duration = .seconds(seconds: 5)

                    // Show the message.
                    SwiftMessages.show(config: config, view: view)
                }
            }
        })
}

#selector(ViewController.callback)