Adicionado método que será chamado no clique do botão

MainActivity.java

public class MainActivity extends Activity {

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

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.activity_main, menu);
		return true;
	}

	/**
	 * Método que será chamado no clique do botão
	 * @param view
	 */
	public void lerQR(View view){
		
	}
	
}