如果应用程序进入后台模式，则会触发Ondisconnect

I have the following code:

我有以下代码：

func OnlineStatus(userID: String){
        handle = Auth.auth().addStateDidChangeListener { (auth, user) in
            if let user = user {
                // User is signed in.
                self.UID = user.uid

                self.connectedRef.observe(.value, with: { snapshot in
                    if let connected = snapshot.value as? Bool, connected {
                        // print("############################ Connected")
                        self.ref.child(self.UID!).child("OnlineStatus").setValue("ON")
                    } else {
                        // print("############################ Not connected")
                        self.ref.child(self.UID!).child("OnlineStatus").setValue("OFF")
                    }
                    self.ref.child(self.UID!).child("OnlineStatus").onDisconnectSetValue("OFF")
                })
            }}
            }
func Onl