Although it is possible for each button to have it's own event handler this must be a pre-existing method.

The simplest way around the problem is to have a single method to handle all button events (default behaviour) but having the event handler identify the button being pressed. All G4P components have 2 public fields the user can do what they like with. They are called tag (String) and tagNo (int).

When you create the button assign a unique number to tagNo and in the event handler use the tagNo to decide what should be done.

The following code creates an array of buttons each having a unique tagNo. Clicking on one of the buttons prints out its tagNo.

1. import guicomponents.*;
2. GButton[] buttons;
3. int nbrButtons = 3;
4. int buttonNo = 101;
5. void setup() {
6.   size(300,300);
7.   buttons = new GButton[nbrButtons];
8.   for(int i = 0; i < nbrButtons; i++) {
9.     buttons[i] = new GButton(this, "Button "+ buttonNo, 10, 10+22*i, 120, 20);
10.     buttons[i].tagNo = buttonNo;
11.     buttonNo++;
12.   }
13. }
14. void handleButtonEvents(GButton button) {
15.   println("You clicked button " + button.tagNo);
16. }
17. void draw() {
18.   background(255);
19. }

I can probably offer alternative advice, but I would need more information about what the buttons are supposed to do.

Hope this helps.

Well, this could work for me but there occured another problem. My basic idea was to create an image button with a different image button. But since you have to create these buttons in the setup method I can't create a button dynamically. I can only set the visibility of the component. My solution for this problem was to create an array of image buttons and resize its length if required. That idea doesn't work anyway. I get only an error message that I can't interpret. A little example how this could work would be great.

But since you have to create these buttons in the setup method I can't create a button dynamically.

This is not true, buttons (in fact any G4P component) can be created at anytime not just in the setup. The array of image buttons was a good idea and writing code to resize the array at run time is fairly straightforward, a better idea might be to use Java's ArrayList which will do the job of a dynaically sized array.

The following code creates a single button in setup. Clicking on this button will create a second button, clicking on either of these buttons create a third and so on. I have limited this to 20 buttons to keep them inside the window.

1. import guicomponents.*;
2. 
   
3. ArrayList<GButton> buttons;
4. GButton temp;
5. int nbrButtons = 1;
6. int buttonNo = 101;
7. int btnClicked = -1;
8. 
   
9. void setup() {
10.   size(300,500);
11.   buttons = new ArrayList<GButton>();
12.   temp = new GButton(this, "Button "+ buttonNo, 10, 10, 120, 20);
13.   temp.tagNo = buttonNo;
14.   buttons.add(temp);
15.   buttonNo++; 
16.   ellipseMode(CORNER);
17. }
18. void handleButtonEvents(GButton button) {
19.   println("You clicked button " + button.tagNo);
20.   btnClicked = button.tagNo - 101; // since thay start at 101
21.   if(buttons.size() < 20) {
22.     temp = new GButton(this, "Button " + buttonNo,10,10+22*buttons.size(),120,20);
23.     temp.tagNo = buttonNo;
24.     buttons.add(temp);
25.     buttonNo++;
26.   }
27. }
28. 
    
29. void draw() {
30.   background(255);
31.   if(btnClicked >= 0){
32.     fill(255,0,0);
33.     noStroke();
34.     ellipse(136,15+btnClicked * 22, 10,10);
35.   }
36. }