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True this parameter was included to make the constructor consistent with the creation of the other GUI components where the first parameter is a refernce to the main PApplet object. Although it is not used in GWindow I kept it for possible future enhancements.

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The following code is taken from the showcase example. It first creates a GWindow then 2 sliders which are then added to the new window.

Moreinfo on GWinData and event handling can be found here.
http://www.lagers.org.uk/g4p/applets/g4p_windowsstarter/index.html

Code:

public void createControlWindow(){
  windControl = new GWindow(this, "Controls",600,400,width/4 + 16,height/4 + 16, false, null);
  sdrHorzPos = new GHorzSlider(this,0,height/4,width/4,16);
  sdrHorzPos.setLimits(pX, 0 ,width - pWidth);
  sdrVertPos = new GVertSlider(this,width/4,0,16,height/4);
  sdrVertPos.setLimits(pY, pnlControls.getTabHeight(), height - pHeight);

  windControl.add(sdrHorzPos);
  windControl.add(sdrVertPos);
  windControl.addData(new GWinData());

  windControl.addDrawHandler(this, "drawController");
  windControl.setExitBehaviour(GWindow.SHUTDOWN_ON_EXIT);
}
 

Since the GWindow applet is basically in a closed class it is not possible to access the normal PApplet event loop.

In G4P when a button is created it will look for a method in the main applet with the following signature
Code:

public void handleButtonEvents(GButton button) 

Assuming you have a number of buttons then you need to check to see which button was used and the event type e.g.

Code:

public void handleButtonEvents(GButton button) {
	if(button == btnUp && button.eventType == GButton.CLICKED)
		txfML2.scroll(GTextField.SCROLL_UP);
	if(button == btnDown && button.eventType == GButton.CLICKED)
		txfML2.scroll(GTextField.SCROLL_DOWN);
	if(button == btnRight && button.eventType == GButton.CLICKED)
		txfML2.scroll(GTextField.SCROLL_RIGHT);
	if(button == btnLeft && button.eventType == GButton.CLICKED)
		txfML2.scroll(GTextField.SCROLL_LEFT);
}
 

This will work for all buttons even if they have been added to another GWindow.

It is also possible for each GUI component (or group of components) to have their own personalised event handler.

All GUI components have a method that can be used to specify their event handler, for instance assume we have a button called btnUp and we want to add a personalised event handler. We can use the statement

Code:

btnUp.addEventHandler(this, "handleUpButtonEvents");
 

This assumes that you have created the following method
Code:

public void handleUpButtonEvents(GButton button){

}
 

Notice the parameter. All event handlers are expected to have a single parameter of the same type as the GUI component. This is the component that generates the event. In this case btnUp.

Hope this answers your question.