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Android Build a Simple Android App (2014) Basic Android Programming Making a Button Do Something

Posted by Jennifer Gerbl
Jennifer Gerbl
8,772 Points

Other way of declaring onClickListener

On research I saw this way of declaring the OnClickListener:

showFactButton.setOnClickListener( new Button.OnClickListener(){
            public void onClick(View view){

            } //end onClick
}); //end setOnClickListener

So what's the difference? And what is more common in programming?

1 Answer

Ben Junya
Ben Junya
12,365 Points
Ben Junya
Ben Junya
12,365 Points

This is a really great question.

In Android, there's 1000+ ways to do the exact same thing, with different pros and cons to each way.

What you did here is the most common way of making an OnClickListener for an individual button:

showFactButton.setOnClickListener(new View.OnClickListener {
     @Override
     public void onClick(View v) {
          // Do something on click
     } //end onClick
} //end new OnClick

Let's say you have a bunch of buttons that all do the same thing - Instead of writing 3 OnClickListeners, you can write just one like this:

public class MainActivity extends ActionBarActivity implements View.OnClickListener {

     // Button declarations omitted for brevity
     @Override
     protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);

         // Button findViewById omitted for brevity

          button1.setOnClickListener(this);
          button2.setOnClickListener(this);
          button3.setOnClickListener(this);
     }

     @Override 
     public void onClick(View v) {
          // Do something when button 1, 2, or 3 is clicked

          // Optionally, you can get which button was clicked by accessing the v argument that's passed to onClick
          int viewID = v.getId();


     }

I certainly hope this helps you out!

Ben Junya
Ben Junya
12,365 Points
Ben Junya
Ben Junya
12,365 Points

If you want to know a little bit of what's happening behind the scenes, an OnClickListener is what's called an interface - which acts like a callback, a common programming pattern that you'll see virtually everywhere.

It starts with this:

protected class MainActivity extends Activity implements View.OnClickListener {}

"Implements" is the keyword we're looking for here.

If you declare a new View.OnClickListener like in the first example to my answer, that means you're creating a new instance of an OnClickListener right off the bat. If you have your activity "Implement" that interface, like in the second example, you just need to pass in "this" as a parameter instead of creating a new instance.

If you want to learn more about interfaces, since they're super awesome and can do lots of cool stuff, you can read up right here: https://docs.oracle.com/javase/tutorial/java/concepts/interface.html