Android OnClickListener - identify a button

Question

Hey. I have the activity:

public class Mtest extends Activity {
  Button b1;
  Button b2;
  public void onCreate(Bundle savedInstanceState) {
    ...
    b1 = (Button) findViewById(R.id.b1);
    b2 = (Button) findViewById(R.id.b2);
    b1.setOnClickListener(myhandler);
    b2.setOnClickListener(myhandler);
    ...
  }
  View.OnClickListener myhandler = new View.OnClickListener() {
    public void onClick(View v) {
      // MY QUESTION STARTS HERE!!!
      // IF b1 do this
      // IF b2 do this
      // MY QUESTION ENDS HERE!!!
    }
  }
}

How do I check which button has been clicked?

Answer 1

You will learn the way to do it, in an easy way, is:

public class Mtest extends Activity {
  Button b1;
  Button b2;
  public void onCreate(Bundle savedInstanceState) {
    ...
    b1 = (Button) findViewById(R.id.b1);
    b2 = (Button) findViewById(R.id.b2);
    b1.setOnClickListener(myhandler1);
    b2.setOnClickListener(myhandler2);
    ...
  }
  View.OnClickListener myhandler1 = new View.OnClickListener() {
    public void onClick(View v) {
      // it was the 1st button
    }
  }
  View.OnClickListener myhandler2 = new View.OnClickListener() {
    public void onClick(View v) {
      // it was the 2nd button
    }
  }
}

Or, if you are working with just one clicklistener, you can do:

View.OnClickListener myOnlyhandler = new View.OnClickListener() {
  public void onClick(View v) {
      if( b1.getId() == ((Button)v).getId() ){
          // it was the first button
      }
      else if( b2.getId() == ((Button)v).getId() ){
          // it was the second button
      }
  }
}

Though, I don't recommend doing it that way since you will have to add an if for each button you use. That's hard to maintain.

Answer 2

In addition to Cristian C's answer (sorry, I do not have the ability to make comments), if you make one handler for both buttons, you may directly compare v to b1 and b2, or if you want to compare by the ID, you do not need to cast v to Button (View has getId() method, too), and that way there is no worry of cast exception.

Answer 3

Hi,

The best way is by switch-ing between v.getId(). Having separate anonymous OnClickListener for each Button is taking up more memory. Casting View to Button is unnecessary. Using if-else when switch is possible is slower and harder to read. In Android's source you can often notice comparing the references by if-else:

if (b1 == v) {
 // ...
} else if (b2 == v) {

I don't know exactly why they chose this way, but it works too.