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The Fragment Manager

Every activity has its own Fragment Manager which is accessible through the method:

getFragmentManager()

The Fragment Manager maintains references to all the fragments within an activity.

You can get references to individual fragments within the activity using the methods

findFragmentById()
findFragmentByTag()

The Fragment Transactions

Adding, removing, swopping fragments are carried out by Fragment Transactions.

So using the Fragment Manager…

How do we create a fragment?

… this is where things change now

MyFragment frag = new MyFragment()
FragmentManager manager = getFragmentManager()

FragmentTransaction transaction = manager.beginTransaction()

… now we can call methods on the transaction object to do stuff to our fragment … e.g.

// takes 3 parameters
// the id of the layout in which you want to add your fragment
// the object of the fragment itself which you initialised before
// a string that can be used to identify the fragment later when you call findFragmentByTag()
transaction.add(R.id.my_layout, frag, “JamesFragment”);
transaction.commit()

Demonstration in code

MainActivity.java

package com.jamesfroggatt.fragments3.app;

import android.app.Activity;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;

public class MainActivity extends Activity {

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

        // here we're going to add the fragment to out activity in java code
        MyFragment frag=new MyFragment();

        FragmentManager manager=getFragmentManager();

        FragmentTransaction transaction= manager.beginTransaction();

        transaction.add(R.id.my_layout_id_in_activity_main_xml, frag, "James Fragment");

        transaction.commit();
    }
}

activity_main.xml

<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"
    android:background="#44FF33"

    android:id="@+id/my_layout_id_in_activity_main_xml" >
    <!-- this id is all the xml we need to get fragment in here-->
    <!--the rest is done in Java -->
</RelativeLayout>

MyFragment.java

package com.jamesfroggatt.fragments3.app;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


public class MyFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        // link the xml fragment (my_fragment_layout.xml) to the java code for the fragment
        // we need to return a view object
        return inflater.inflate(R.layout.my_fragment_layout, container, false);
    }
}

my_fragment_layout.xml

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

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#225588" >>

    <TextView
        android:layout_margin="60dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="This is my_fragment_layout.xml fragment"
        android:id="@+id/textView" />
</LinearLayout>

Gives the following result:

Portrait

Landscape