Android : Why am I not allowed to use setOnClickListener in this situation?

This makes no sense, I am given an error saying that setOnClickListener can't be applied to MainActivity. But i've made other projects where I've never encountered this problem. What's going on?

public class MainActivity extends ActionBarActivity {

Button button;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    button = ((Button) findViewById(R.id.button));

    button.setOnClickListener(this);

}