Future<FirebaseUser> signInUser([var myuserdata,var mypasswrd
      ,frouter,srouter]
      )async{
      FirebaseUser firebaseUser = await FirebaseAuth.instance
      .signInWithEmailAndPassword(email:myuserdata,password:mypasswrd).then((onValue){
          if(onValue.uid != null){
// main page
        print('object at non-null uid ${onValue.uid}');
        frouter;
      }
     if(onValue.uid == null){
//error page
        srouter;
      print('object at null uid ${onValue.uid}');
      }
      });
      print('user id :${firebaseUser.uid}');
    return firebaseUser;
    }