Default fragment in activity

Question

I've seen many posts on this matter, but I can't figure it out for my code. I have created a tabbed activity and set three buttons at the bottom. The buttons switch between different fragments. A button in a MainActivity opens this tabbed activity, but the problem is that the fragment layout is empty (see image below).

The buttons work perfectly and send me to the right fragments, but when it opens, no fragments are loaded.

The code, which I build following an YouTube tutorial looks like this:

TabbedActivity.class

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.view.MenuItem;

public class TabbedActivity extends AppCompatActivity {

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

        BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
    }

    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {


        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            android.support.v4.app.FragmentManager fragmentManager = getSupportFragmentManager();
            android.support.v4.app.FragmentTransaction transaction = fragmentManager.beginTransaction();
            int intentFragment = getIntent().getExtras().getInt("frgToLoad");
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    transaction.replace(R.id.content,new Fragment_B1()).commit();
/*                    mTextMessage.setText(R.string.title_home);*/
                    return true;
                case R.id.navigation_dashboard:
                    transaction.replace(R.id.content,new Fragment_B2()).commit();
                    /*mTextMessage.setText(R.string.title_dashboard);*/
                    return true;
                case R.id.navigation_notifications:
                    transaction.replace(R.id.content,new Fragment_B3()).commit();
                    /*mTextMessage.setText(R.string.title_notifications);*/
                    return true;

            }
            return false;
        }
    };

}

The fragments have the same code pattern inside, which is basic and it makes no point to add it here. The xml of the TabbedActivity looks like this:

<?xml version="1.0" encoding="utf-8"?>

<android.support.constraint.ConstraintLayout 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:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="TabbedActivity">

    <FrameLayout
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintTop_toBottomOf="@+id/appbar">

    </FrameLayout>

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/navigation"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="0dp"
        android:layout_marginStart="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/navigation" />

</android.support.constraint.ConstraintLayout>

Can anyone help me to figure out how to open Fragment_B1 by default? I have tried adding the code from the best answer from here, but still doesn't work.

Answer 1

You can just added the original fragment direct on the onCreate, like this:

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

    BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

    if(savedInstanceState == null) {
       getSupportFragmentManager().
       beginTransaction().replace(R.id.content,new Fragment_B1()).commit();
    }
 }