verifyCode.dart

_verifyCode() async {
    final AuthCredential credential = PhoneAuthProvider.getCredential(
        verificationId: _verificationId, smsCode: _controllerCode.text);
    final FirebaseUser user =
        (await _auth.signInWithCredential(credential)).user;
    final FirebaseUser currentUser = await _auth.currentUser();
    assert(user.uid == currentUser.uid);
    if (user != null) {
      Navigator.pop(context);
      Navigator.push(
          context,
          MaterialPageRoute(
              builder: (context) => SecondScreen(
                    user: user,
                  )));
    }
  }