Android, why can't set a fragment from a variable?

Question

Android

Hello, I have a problem, my phone shows a black screen when I try to insert my class object into FragmentTransaction

LoginFragment lf = new LoginFragment();
fTrans = getFragmentManager().beginTransaction();
fTrans.add(R.id.loginContainer, lf).commit();

But if I add an instance of the class, then everything works fine

fTrans = getFragmentManager().beginTransaction();
fTrans.add(R.id.loginContainer,
    new LoginFragment()).commit();

The problem is that I'm trying to do this on my LG, which is 4.0.3, and on 4.2.2 and above everything works fine. Please tell me what is causing this bug.

Answer 1

At first glance, everything should work. If specific to version 4.0.3, or device specific, make sure to use the support library classes.

Answer 2

What if Fragment login = new LoginFragment();?

Answer 3

Try using replace instead of add.