In Android, the Fragment is the part of the Activity that represents a portion of the User Interface(UI) on the screen. It is the modular section of the android activity that is very helpful in creating UI designs that are flexible in nature and auto-adjustable based on the device screen size. onBackPressed() is a method that is to be implemented in our activity in order to run a function after pressing the back button. Usually, onBackPressed() method is used to implement some method after moving back from an activity.
@Override
public void onBackPressed() {
super.onBackPressed();
}
Since there is no override onBackPressed() method to implement in Fragments. There is one method of implementing onBackPressed() method to call the interface method which are implemented in the fragment using onBackPressed() method of the activity containing fragment layout.
Step by Step Implementation
Step 1: Create a java class(Backpreessedlistener) and here, we implement an interface having a method onBackPressed()(any name as we want) and override accordingly.
public interface Backpressedlistener {
void onBackPressed();
}
Step 2: Implement the method of interface write a function to implement on back pressed in the fragment.
@Override
public void onBackPressed() {
Toast.makeText(getContext(),"back button pressed",Toast.LENGTH_LONG).show();
}
Step 3: Create the frame layout in the activity_main.xml file
<FrameLayout android:id="@+id/fragl" android:layout_width="match_parent" android:layout_height="match_parent" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" />
Step 4: Create the object of the interface.
public class BlankFragment extends Fragment implements Backpressedlistener {
View v;
// creating object of Backpressedlistener interface
public static Backpressedlistener backpressedlistener;
// Driving code
............................
}
Step 5: In an fragment class (BlankFragment) implement onpause() method and onResume() method, pass null to backpressedlistener in onPause() method and context of fragment to backpressedlistener in onResume() method.
// Overriding onPause() method
@Override
public void onPause() {
// passing null value
// to backpressedlistener
backpressedlistener=null;
super.onPause();
}
// Overriding onResume() method
@Override
public void onResume() {
super.onResume();
// passing context of fragment
// to backpressedlistener
backpressedlistener=this;
}
Step 6: In Mainactivity, Implement onBackPressed() method and access the backpressedlistener.
@Override
public void onBackPressed() {
super.onBackPressed();
if(BlankFragment.backpressedlistener!=null){
// accessing the backpressedlistener of fragment
BlankFragment.backpressedlistener.onBackPressed();
}
}
There are the following Layout and code for the Implementation of onBackPressed() in Fragments.
Complete Code
Navigate to the app > res > layout > activity_main.xml and add the below code to that file. Below is the code for the activity_main.xml file.
XML
<?xml version="1.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayout android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> <FrameLayout android:id="@+id/fragl" android:layout_width="match_parent" android:layout_height="match_parent" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" /> </androidx.constraintlayout.widget.ConstraintLayout> |
Go to the MainActivity.java file and refer to the following code. Below is the code for the MainActivity.java file.
Java
package com.example.gfg; import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;import android.widget.Button; public class MainActivity extends AppCompatActivity { @Override public void onBackPressed() { // super.onBackPressed(); if(BlankFragment.backpressedlistener!=null){ BlankFragment.backpressedlistener.onBackPressed(); } } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); getSupportFragmentManager().beginTransaction() .setReorderingAllowed(true) .add(R.id.fragl,BlankFragment.class,null) .commit(); }} |
fragment_blank.xml:
XML
<?xml version="1.0" encoding="utf-8"?><FrameLayout android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".BlankFragment"> <!-- TODO: Update blank fragment layout --> <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:layout_gravity="center" android:gravity="center" android:text="@string/hello_blank_fragment" /> </FrameLayout> |
BlankFragment.java:
Java
package com.example.gfg; import android.os.Bundle;import androidx.fragment.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.Toast; public class BlankFragment extends Fragment implements Backpressedlistener { View v; public static Backpressedlistener backpressedlistener; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { v=inflater.inflate(R.layout.fragment_blank, container, false); return v; } @Override public void onPause() { backpressedlistener=null; super.onPause(); } @Override public void onResume() { super.onResume(); backpressedlistener=this; } @Override public void onBackPressed() { Toast.makeText(getContext(),"back button pressed",Toast.LENGTH_LONG).show(); } } |
Backpressedlistener.java:
Java
package com.example.gfg; public interface Backpressedlistener { void onBackPressed();} |
