在导航活动中屏幕旋转期间片段更改

Question

目前我正在研究导航Activity和片段。我正在使用正常工作的content_main布局替换片段。但是当我旋转屏幕时，片段就会消失，导航活动就会显示出来。当我旋转屏幕时，如何保存碎片的状态，当我旋转屏幕然后片段状态将被保存并且不应该消失，当我单击后退按钮时，将显示活动。 这是我的代码：

 public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();
   if (id == R.id.login) {
        getFragmentManager().beginTransaction().replace(R.id.frameLayout,new LoginFragment()).addToBackStack(null).commit();
    } else if (id == R.id.signup) {
        }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

这是我的登录片段：

  public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.fragment_login, container, false);

    btnLogin = (Button) view.findViewById(R.id.btn_login);
    btnCreateAccount = (Button) view.findViewById(R.id.createAccount);
    forgotPassword = (TextView)view.findViewById(R.id.tv_forgotPassword);
    et_emailId = (EditText)view.findViewById(R.id.input_email);
    et_Password = (EditText)view.findViewById(R.id.input_password);

    loginLayout = (ConstraintLayout) view.findViewById(R.id.homeMain);



    btnCreateAccount.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            getFragmentManager().beginTransaction().replace(R.id.frameLayout, new SignUpFragment()).addToBackStack(null).commit();
        }
    });

    forgotPassword.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            getFragmentManager().beginTransaction().replace(R.id.frameLayout,new ForgotPasswordFragment()).addToBackStack(null).commit();
        }
    });



    return view;

}

@Override
public void onStart() {
    super.onStart();
    Log.e(TAG,"start");
}

@Override
public void onResume() {
    super.onResume();
    Log.e(TAG,"Resume");
}

@Override
public void onPause() {
    super.onPause();
    Log.e(TAG,"Pause");
}

@Override
public void onStop() {
    super.onStop();
    Log.e(TAG,"stop");
}

@Override
public void onClick(View v) {
    switch (v.getId()){
        case R.id.btn_login:
            checkValidation();
            break;
    }
}

private void checkValidation() {
    emailId = et_emailId.getText().toString();
    password = et_Password.getText().toString();
    if(emailId.equals("") || emailId.length() == 0
            || password.equals("") || password.length() == 0){

         Toast.makeText(getActivity(),"All fields  are required",Toast.LENGTH_SHORT).show();
    }else {
        Toast.makeText(getActivity(),"login code here",Toast.LENGTH_SHORT).show();
    }
}