Button action-Android app

Question

I am practicing from the book Hello,Android ed3.There is an example code on creating an action button to display 'About' the game.I have edited all the necessary xml files.I am getting error in the following code.logcat is showing nullpointer exception in line 10: about.Button.setClickListener(this).Please help.Also i have been unable to understand 'this' parameter.Any hep?

public class Sudoku extends Activity implements OnClickListener {
private static final String TAG = "Sudoku";
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      // Set up click listeners for all the button
      View aboutButton = findViewById(R.id.about_button);
      aboutButton.setOnClickListener(this);

   }

   public void onClick(View v) {
          switch (v.getId()) {
          case R.id.about_button:
             Intent i = new Intent(this, About.class);
             startActivity(i);
             break;
    }

} }

Answer 1

public class Sudoku extends Activity implements OnClickListener {
private static final String TAG = "Sudoku";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);
   // Set up click listeners for all the button
   Button aboutButton = (Button) findViewById(R.id.about_button);
  aboutButton.setOnClickListener(this);

}

public void onClick(View v) {
      if(v == aboutButton){
         Intent i = new Intent(this, About.class);
         startActivity(i);
         break;
}

Try this one... just changed 2-3 lines...

Answer 2

Looks like you dont have "about_button" button in the xml file. Did you give the same name for the button in xml?