Estou sofrendo com fragmentos aninhados. Eu tenho uma atividade principal que chama um fragmento 1 que por sua vez chama um fragmento através de um botão. O fragmento frag2 é bem instanciado, mas a tela está em branco. Existe algo óbvio no meu código?

Atividade principal

import android.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        FragmentManager fragmentManager;
        Frag1 f1 = new Frag1();
        fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.content_frame,
                f1).commit();
    }
}

mainactivity xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.narb.nestedfragments.MainActivity">


    <FrameLayout
        android:id="@+id/content_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

</RelativeLayout>

Fragmento 1 e seu layout xml:

import android.app.FragmentTransaction;
import android.content.Context;
import android.os.Bundle;
import android.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.RelativeLayout;


/**
 * A simple {@link Fragment} subclass.
 */
public class Frag1 extends android.app.Fragment {
    Context context;
    private Button back1;
    RelativeLayout rl1;

    public Frag1() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootview = null;
        rootview = inflater.inflate(R.layout.fragment_frag1, container, false);
        return rootview;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        context = getActivity().getApplicationContext();

        initFindView();

        back1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Log.i("frag1","createdview");
                //getActivity().getFragmentManager().popBackStackImmediate();
                rl1.setVisibility(View.INVISIBLE);
                FragmentTransaction ft = getFragmentManager().beginTransaction();
                Frag2 f2 = new Frag2();
                ft.replace(R.id.fl1, f2);
                ft.addToBackStack(null);
                ft.commit();
            }
        });

    }

    private void initFindView(){
        back1 = (Button) getActivity().findViewById(R.id.btn1);
        rl1 = (RelativeLayout) getActivity().findViewById(R.id.rl1);
    }
}

É normal que eu precise tornar meu layout frag 1 invisível antes de chamar frag2?

e finalmente meu fragmento 2 e seu layout. Eu vejo o log da frag 2, mas a tela está vazia:

import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;


public class Frag2 extends Fragment {
    Context context;
    private Button btn2;

    public Frag2() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootview;
        rootview = inflater.inflate(R.layout.fragment_frag2, container, false);
        Log.i("frag2","createdview");
        return rootview;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        context = getActivity().getApplicationContext();
        Log.i("frag2","onactivitycreated");

        btn2 = (Button) getActivity().findViewById(R.id.btn2);
        btn2.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Log.i("frag2","onactivitycreated");
            }
        });

    }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.narb.nestedfragments.Frag2">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="Test 2" />

    <Button
        android:id="@+id/btn2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="60dp"
        android:text="back"
        />
</RelativeLayout>