问Firebase数据库中的“. .info/serverTimeOffset”不刷新

EN

    class MainActivity : AppCompatActivity() {


        override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
            Log.i("ph","MainActivity OnCreate")
            calculateDelay(this)
        }

        override fun onDestroy() {
            super.onDestroy()
            Log.i("ph","MainActivity OnDestroy")
        }

        private fun calculateDelay(ac: Context) {
            FirebaseDatabase.getInstance().goOffline()
            FirebaseDatabase.getInstance().goOnline()
            val offsetRef = FirebaseDatabase.getInstance().getReference(".info/serverTimeOffset")
            offsetRef.addListenerForSingleValueEvent(object : ValueEventListener {
                override fun onDataChange(snapshot: DataSnapshot) {

                    val systemTimeOffset = snapshot.getValue(Long::class.java) ?: 0L
                    val estimatedOffset =
                        System.currentTimeMillis() + systemTimeOffset - SystemClock.elapsedRealtime()
                    val estimatedServerTimeMs =
                        estimatedOffset + SystemClock.elapsedRealtime()
                    Log.i("ph","Main Time " + getdate(estimatedServerTimeMs, "dd/MM/yyyy hh:mm:ss.SSS"))
                    val sPreference = SPreference(ac) // my preference class 
                    sPreference.putTD(estimatedOffset) // saving to preference
                }

                override fun onCancelled(p0: DatabaseError) {
                    TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
                }
            })
        }
    }