G4P - Defining handleButtonEvents(..) in a Class

I’m coding native java classes using the Processing 3 IDE. Using G4P as my GUI library I’m trying to encapsulate one of my logical GUI components inside its own class, including the event handler for associated events. However, when I define a by-control-type event handler within this class G4P doesn’t see it and only appears to be looking for such event handlers within the main processing ‘implied’ class. Am I perhaps missing something as to how to have such event handlers defined within other classes of my program?


G4P allows you to specify the object and the class instance method to be used to handle events from a particular button. The following sketch demonstrates this

import g4p_controls.*;

Foo foo;

GButton btn;

void setup() {
  size(300, 300);
  // Create object to handle events from the button
  foo = new Foo();
  btn = new GButton(this, 10, 10, 100, 40, "Click Me!");
  btn.addEventHandler(foo, "buttonClick");

void draw() {
  text(foo.clickCount(), 100, 150);

// Make this a top-level class
public static class Foo {
  private int clickCount = 0;

  public Foo() {

  // Event handler for a G4P button
  public void buttonClick(GButton button, GEvent event) { 

  public int clickCount() {
    return clickCount;

Thank you for such a timely response, and on a weekend too. I see my mistake, I didn’t read the API close enough and simply assumed that the first argument to addEventHandler(…) needed to be a sketch like many of the others. But with your example and rereading the reference doc I see that it is actually meant to be the object containing the callback. This solves my issue, thank you. Also, thanks for contributing such a nice GUI library to the processing community, I’m finding it very useful.