Android Fragments

Editor — Sun, 11 Jul 2021 05:28:24 +0000

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.

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

 
    android:layout_width="fill_parent"  
    android:layout_height="fill_parent" >  
  
            android:id="@+id/fragment2"  
        android:name="com.example.fragmentexample.Fragment2"  
        android:layout_width="0px"  
        android:layout_height="match_parent"   
        android:layout_weight="1"  
        />  
  
            android:id="@+id/fragment1"  
        android:name="com.example.fragmentexample.Fragment1"  
        android:layout_width="0px"  
        android:layout_height="match_parent"  
        android:layout_weight="1"  
         />  
  
  

File: fragment1.xml

  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    android:orientation="vertical"  
    android:background="#00ff00"  
     >  
  
            android:id="@+id/textView1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:text="fragment frist"  
        android:textAppearance="?android:attr/textAppearanceLarge" />

File: fragment2.xml

  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    android:orientation="vertical"  
    android:background="#0000ff"  
     >  
  
            android:id="@+id/textView1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:text="Second Fragment"  
        android:textAppearance="?android:attr/textAppearanceLarge" />

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);  
    }  
  
} 

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 Activity Lifecycle | android lifecycle

Editor — Sun, 11 Jul 2021 04:58:44 +0000

What is Android Activity

- An activity represents a single screen with a user interface just like window or frame of Java .Android activity is the subclass of Context Theme Wrapper class.
  - Activities are a fundamental building block of Android applications and they can exist in a number of different states.

- The activity lifecycle begins with instantiation and ends with destruction, and includes many states in between.
- When an activity changes state, the appropriate lifecycle event method is called, notifying the activity of the impending state change and allowing it to execute code in order to adapt to that change.
- Android Activity Lifecycle is controlled by 7 methods of android.app.Activity class.
- An activity is the single screen in android. It is like window or frame of Java.
- By the help of activity, you can place all your UI components or widgets in a single screen.
- The 7 lifecycle method of Activity describes how activity will behave at different states.

Android Activity Lifecycle methods

Let’s see the 7 lifecycle methods of android activity.

Method	Description
onCreate	called when activity is first created.
onStart	called when activity is becoming visible to the user.
onResume	called when activity will start interacting with the user.
onPause	called when activity is not visible to the user.
onStop	called when activity is no longer visible to the user.
onRestart	called after your activity is stopped, prior to start.
onDestroy	called before the activity is destroyed.

It provides the details about the invocation of life cycle methods of activity. In this example, we are displaying the content on the logcat.
- File: MainActivity.java

 
package com.example.activitylifecycle;  
import android.os.Bundle;  
import android.app.Activity;  
import android.util.Log;  
import android.view.Menu;  
public class MainActivity extends Activity {  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
        Log.d("lifecycle","onCreate invoked");  
    }  
    @Override  
    protected void onStart() {  
        super.onStart();  
         Log.d("lifecycle","onStart invoked");  
    }  
    @Override  
    protected void onResume() {  
        super.onResume();  
         Log.d("lifecycle","onResume invoked");  
    }  
    @Override  
    protected void onPause() {  
        super.onPause();  
         Log.d("lifecycle","onPause invoked");  
    }  
    @Override  
    protected void onStop() {  
        super.onStop();  
         Log.d("lifecycle","onStop invoked");  
    }  
       @Override  
    protected void onRestart() {  
        super.onRestart();  
         Log.d("lifecycle","onRestart invoked");  
    }     
    @Override  
    protected void onDestroy() {  
        super.onDestroy();  
         Log.d("lifecycle","onDestroy invoked");  
    }  
} 

You will not see any output on the emulator or device. You need to open logcat.

Now see on the logcat: on Create, on Start and on Resume methods are invoked.

Now click on the HOME Button. You will see on Pause method is invoked.

After a while, you will see on Stop method is invoked.

Now see on the emulator. It is on the home. Now click on the center button to launch the app again.

Now click on the lifecycle activity icon.

Now see on the logcat: on Restart, on Start and on Resume methods are invoked.

If you see the emulator, application is started again.

Now click on the back button. Now you will see onPause methods is invoked.

After a while, you will see onStop and onDestroy methods are invoked.

android system - Wikitechy

Android Fragments

What is Fragments?

Android Fragment Lifecycle

Using a fragment

Creating a fragment

How to create a Fragment in Android Studio

Android Fragment Classes

Android Fragment Example

activity_main.xml

File: fragment1.xml

File: fragment2.xml

MainActivity class

File: MainActivity.java

File: Fragment1.java

File: Fragment2.java

Output

Android Activity Lifecycle | android lifecycle

What is Android Activity

Android Activity Lifecycle methods