Android Fragment Lifecycle

Fragments were added to the Android API in Honeycomb(API 11).

1. android.app.Fragment : The base class for all fragment definitions
2. android.app.FragmentManager : The class for interacting with fragment objects inside an activity
3. android.app.FragmentTransaction : The class for performing an atomic set of fragment operations When using a compatibility package library provided by Google, the following classes are used for implementation.

• android.support.v4.app.FragmentActivity : The base class for all activities using compatibility-based fragment (and loader) features
• android.support.v4.app.Fragment
• android.support.v4.app.FragmentManager
• android.support.v4.app.FragmentTransaction

Here’s a sample fragment using onCreateView() for its implementation:

public class SampleFragment extends Fragment {

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

        View rootView = inflater.inflate(R.layout.fragment_sample, parentViewGroup, false);
        return rootView;
    }
}

onCreateView() method gets a LayoutInflater, a ViewGroup and a Bundle as parameters. LayoutInflater is an component which can create View instance based on layout XML files. As you can see, the example actually does that by calling layout.inflate(). inflate() method takes three parameters: The id of a layout XML file (inside R.layout), a parent ViewGroup into which the fragment’s View is to be inserted, and a third boolean telling whether the fragment’s View as inflated from the layout XML file should be inserted into the parent ViewGroup. In this case we’ll pass false because the View will be attached to the parent ViewGroup elsewhere, by some of the Android code we call. When you pass false as last parameter to inflate(), the parent ViewGroup is still used for layout calculations of the inflated View, so you cannot pass null as parent ViewGroup . ViewGroup parameter of onCreateView() is the parent ViewGroup into which the View of the fragment is to be inserted. This is a ViewGroup inside the activity that will “host” the fragment. Bundle parameter of onCreateView() is a Bundle in which the fragment can save data, just like in an Activity.

Android fragments example project comprises of a single activity holding two fragments: TextFragment and MenuFragment respectively.

The MainActivity holds the two fragments TextFragment and MenuFragment. So lets begin with defining the fragments in the xml layout activity_main.xml

<LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:weightSum="1.0">

    <fragment
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        class="journaldev.com.fragments.fragments.MenuFragment"
        android:id="@+id/fragment"
        android:layout_weight="0.5"/>
    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        class="journaldev.com.fragments.fragments.TextFragment"
        android:id="@+id/fragment2"
        android:layout_weight="0.5"/>
</LinearLayout>

As we can see the class files of the fragments that are a part of this activity are defined as class=“journaldev.com.fragments.fragments.TextFragment” The fragment classes and their layouts are defined as shown in the snippets below.

package journaldev.com.fragments.fragments;

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

import journaldev.com.fragments.R;
public class TextFragment extends Fragment {
    TextView text,vers;

    @Override

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

        View view = inflater.inflate(R.layout.text_fragment, container, false);
        text= (TextView) view.findViewById(R.id.AndroidOs);
        vers= (TextView)view.findViewById(R.id.Version);


        return view;

    }
    public void change(String txt, String txt1){
        text.setText(txt);
        vers.setText(txt1);

    }
}

text_fragment.xml

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

<LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:gravity="center"
    android:background="#5ba4e5"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="40px"
        android:textColor="#ffffff"
        android:layout_gravity="center"
        android:id="@+id/AndroidOs"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:textColor="#ffffff"
        android:textSize="30px"
        android:id="@+id/Version"/>

</LinearLayout>

The TextFragment comprises of textviews holding the android version name and number.

package journaldev.com.fragments.fragments;

import android.app.ListFragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import journaldev.com.fragments.R;
public class MenuFragment extends ListFragment {
    String[] AndroidOS = new String[] { "Cupcake","Donut","Eclair","Froyo","Gingerbread","Honeycomb","Ice Cream SandWich","Jelly Bean","KitKat" };
    String[] Version = new String[]{"1.5","1.6","2.0-2.1","2.2","2.3","3.0-3.2","4.0","4.1-4.3","4.4"};
    @Override

    public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle savedInstanceState) {
        View view =inflater.inflate(R.layout.list_fragment, container, false);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),
                android.R.layout.simple_list_item_1, AndroidOS);
        setListAdapter(adapter);

        return view;

    }
    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        TextFragment txt = (TextFragment)getFragmentManager().findFragmentById(R.id.fragment2);
        txt.change(AndroidOS[position],"Version : "+Version[position]);
        getListView().setSelector(android.R.color.holo_blue_dark);
    }
}

list_fragment.xml

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

<LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@android:id/list" />
</LinearLayout>

The MenuFragment displays a ListView. As we can see here, the layout of ListView is default simple_list_item_1 opposed to the custom layout we created for the ListView in the previous article. The MainActivity invokes the setContentView from the onCreate Method, that’s it. The fragments are called from the xml file. Alternatively we can add the fragments from the activity class using FragmentManager as shown in the snippet below:

getFragmentManager()
                  .beginTransaction()
                  .add(R.id.fragmentParentViewGroup, new MyFragment())
                  .commit();

Here the id fragmentParentViewGroup belongs to the FrameLayout shown below:

<FrameLayout xmlns:android="https://schemas.android.com/apk/res/android"
             xmlns:tools="https://schemas.android.com/tools"
             android:id="@+id/fragmentParentViewGroup"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             tools:context=".MyActivity"
             tools:ignore="MergeRootFrame" />

Below shows the output produced by our project, you can see that two fragments are present here and when you select any one of them in the left side fragment, data gets populated in the right side fragment. You can download final android fragment project from below link.

Download Android Fragment Project