Handle the BACK key by overriding onKeyDown()

onKeyDown(int keyCode, KeyEvent event) will be called when a key was pressed down and not handled by any of the views inside of the activity.

package com.BackButton;

import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.widget.Toast;

public class AndroidBackButtonActivity extends Activity {
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
   }

 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
  // TODO Auto-generated method stub
  //return super.onKeyDown(keyCode, event);
  if (keyCode == KeyEvent.KEYCODE_BACK){
   //Process onKeyDown event of BACK key
   
   Toast.makeText(AndroidBackButtonActivity.this,
     "BACK key pressed",
     Toast.LENGTH_LONG).show();
   
   return true; //processed
  }else{
   //Pass to original method to handle the key event
   return super.onKeyDown(keyCode, event);
  }
  

 }
}

Related Post:
- For API level 5 (Android 2.1) or higher, onBackPressed() callback method is a alternative to handle BACK key.