android - Firebase OnDataChange function triggered wrong time? -

i have basic program testing firebase. have 2 buttons: first writing firebase database "a", second writing "b" , checking them service:

myref.addvalueeventlistener(new valueeventlistener() {         @override         public void ondatachange(datasnapshot datasnapshot) {             string value = datasnapshot.getvalue(string.class);             if(value=="a")             {                 tonegenerator tonegenerator= new   tonegenerator(audiomanager.stream_dtmf,tonegenerator.max_volume);                 //this play tone 2 seconds.                 tonegenerator.starttone(tonegenerator.tone_dtmf_1, 500);                 try {                     thread.sleep(1000);                 } catch (interruptedexception e) {                     e.printstacktrace();                 }                 tonegenerator.starttone(tonegenerator.tone_dtmf_1, 500);              }              if(value=="b")             {                 tonegenerator tonegeneratora= new   tonegenerator(audiomanager.stream_dtmf,tonegenerator.max_volume);                 //this play tone 2 seconds.                 tonegeneratora.starttone(tonegenerator.tone_dtmf_3, 500);                 try {                     thread.sleep(1000);                 } catch (interruptedexception e) {                     e.printstacktrace();                 }                 tonegeneratora.starttone(tonegenerator.tone_dtmf_3, 500);              } 

the problem is, have no internet connection, mean can't write firebase database or b when click buttons, ondatachanged function still triggered. want when database data changed.

update : when changed database manually ondatachange still not triggered.its working once while program starting.

use childeventlistener can put code want execute inside onchildchanged() method.