Android Fragments

What is Fragments?

  • A Fragment is a piece of an activity which enable more modular activity design. It will not be wrong if we say, a fragment is a kind of sub-activity. A fragment has its own layout and its own behavior with its own life cycle callbacks.
  • You can add or remove fragments in an activity while the activity is running.
  • You can combine multiple fragments in a single activity to build a multi-plane UI.
  • Android Fragment is the part of activity, it is also known as sub-activity. There can be more than one fragment in an activity. Fragments represent multiple screen inside one activity.
  • Android fragment lifecycle is affected by activity lifecycle because fragments are included in activity.
  • Each fragment has its own life cycle methods that is affected by activity life cycle because fragments are embedded in activity.
  • The Fragment Manager class is responsible to make interaction between fragment objects.

Android Fragment Lifecycle

  • The lifecycle of android fragment is like the activity lifecycle. There are 12 lifecycle methods for fragment.
No. Method Description
1. onAttach(Activity) it is called only once when it is attached with activity.
2. onCreate(Bundle) It is used to initialize the fragment.
3. onCreateView(LayoutInflater, ViewGroup, Bundle) creates and returns view hierarchy.
4. onActivityCreated(Bundle) It is invoked after the completion of onCreate() method.
5. onViewStateRestored(Bundle) It provides information to the fragment that all the saved state of fragment view hierarchy has been restored.
6. onStart() makes the fragment visible.
7. onResume() makes the fragment interactive.
8. onPause() is called when fragment is no longer interactive.
9. onStop() is called when fragment is no longer visible.
10. onDestroyView() allows the fragment to clean up resources.
11. onDestroy() allows the fragment to do final clean up of fragment state.
12. onDetach() It is called immediately prior to the fragment no longer being associated with its activity.
android fragment life cycle

Using a fragment

  • The general steps to use a Fragment:
    • Create a subclass of Fragment.
    • Create a layout for the Fragment.
    • Add the Fragment to a host Activity, either statically or dynamically.

Creating a fragment

  • To create a Fragment in an app, extend the Fragment class, then override key lifecycle methods to insert your app logic, similar to the way of Activity class.
  • Instead of extending the base Fragment class, you can extend one of these other, more specific Fragment subclasses:
    • DialogFragment : Displays a floating dialog, such as a date picker or time picker.
    • ListFragment : Displays a list of items that are managed by an adapter (such as a SimpleCursorAdapter).
    • PreferenceFragment : Displays a hierarchy of Preference objects as a list, similar to PreferenceActivity. This is useful when creating a “settings” Activity for your app.

How to create a Fragment in Android Studio

  • In Project: Android view, expand app > java and select the folder containing the Java code for your app.
  • Choose File > New > Fragment > Fragment (Blank).
  • Name the Fragment something like SimpleFragment, or use the supplied name (BlankFragment).
  • If your Fragment has a UI, check the Create layout XML option if it is not already checked. Other options include:
    • Include fragment factory methods : Include sample factory method code to initialize the Fragment arguments in a way that encapsulates and abstracts them. Select this option if the number of arguments would make a constructor too complex.
    • Include interface callbacks : Select this option if you want to include sample code that defines an interface in the Fragment with callback methods that enable the Fragment to communicate with its host Activity.
  • Click Finish to create a Fragment.

Android Fragment Classes

  • Fragments were added to the Android API in Honeycomb(API 11).
    • android.app.Fragment : The base class for all fragment definitions
    • android.app.FragmentManager : The class for interacting with fragment objects inside an activity
    • 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

Android Fragment Example

  • Let’s have a look at the simple example of android fragment.

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:layout_width="fill_parent"  
    android:layout_height="fill_parent" >  
  
    <fragment  
        android:id="@+id/fragment2"  
        android:name="com.example.fragmentexample.Fragment2"  
        android:layout_width="0px"  
        android:layout_height="match_parent"   
        android:layout_weight="1"  
        />  
  
    <fragment  
        android:id="@+id/fragment1"  
        android:name="com.example.fragmentexample.Fragment1"  
        android:layout_width="0px"  
        android:layout_height="match_parent"  
        android:layout_weight="1"  
         />  
  
</LinearLayout>

File: fragment1.xml

<?xml version="1.0" encoding="utf-8"?>  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    android:orientation="vertical"  
    android:background="#00ff00"  
     >  
  
    <TextView  
        android:id="@+id/textView1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:text="fragment frist"  
        android:textAppearance="?android:attr/textAppearanceLarge" />  
  
</LinearLayout>

File: fragment2.xml

<?xml version="1.0" encoding="utf-8"?>  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    android:orientation="vertical"  
    android:background="#0000ff"  
     >  
  
    <TextView  
        android:id="@+id/textView1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:text="Second Fragment"  
        android:textAppearance="?android:attr/textAppearanceLarge" />  
  
</LinearLayout>

MainActivity class

File: MainActivity.java

package com.example.fragmentexample;  
  
import android.os.Bundle;  
import android.app.Activity;  
import android.view.Menu;  
public class MainActivity extends Activity {  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
    }  
}

File: Fragment1.java

ackage com.example.fragmentexample;  
  
import android.app.Fragment;  
import android.os.Bundle;  
import android.view.LayoutInflater;  
import android.view.View;  
import android.view.ViewGroup;  
  
public class Fragment1 extends Fragment {  
    @Override  
    public View onCreateView(LayoutInflater inflater, ViewGroup container,  
            Bundle savedInstanceState) {  
        // TODO Auto-generated method stub  
        return inflater.inflate(R.layout.fragment1,container, false);  
    }  
  
}
android activity and fragment life cycle

File: Fragment2.java

package com.example.fragmentexample;  
  
import android.app.Fragment;  
import android.os.Bundle;  
import android.view.LayoutInflater;  
import android.view.View;  
import android.view.ViewGroup;  
  
public class Fragment2 extends Fragment {  
      
    public View onCreateView(LayoutInflater inflater, ViewGroup container,  
            Bundle savedInstanceState) {  
        // TODO Auto-generated method stub  
        return inflater.inflate(R.layout.fragment2,container, false);  
    }  
  
}

Output

Android Fragments

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