Using one JavaFX method for multiple Buttons

Question

Right now I'm using Eclipse Luna, JavaFX and SceneBuilder. I have ~40 buttons, and I'd like to use a generic "buttonPressed" action method that every button can use. Something like this:

public void buttonPressed(ActionEvent event, Button b) {
    b.setText("Pressed");
}

When I change the On Action panel in SceneBuilder however, I get the following Exception when I try to run my program:

javafx.fxml.LoadException: Error resolving onAction='#buttonPressed', either the event handler is not in the Namespace or there is an error in the script.

Is there a step I missed? Or does anyone know of an alternate way to use one method to control the on-click behavior of multiple buttons?

Any help appreciated!

Just to add to my initial question; It seems like the problem is passing Button b in as a parameter. Removing it, and specifying a button inside the method remedies the Exception ( but not the problem at hand, as the method can now only be used by one button ). Is there perhaps a different way of locating which button is being pressed and then passing that to the method? — JonnyH
– JonnyH, Commented Feb 2, 2015 at 21:23

James_D · Accepted Answer · 2015-02-02 21:31:06Z

4

As in your comment, the only signatures allowed for an onAction attribute are either zero arguments, or a single argument which is an ActionEvent.

You can get the source of the event as follows:

@FXML
public void buttonPressed(ActionEvent event) {
    Object source = event.getSource();
    // ...
}

and of course if you know you only registered the handler on buttons, you can do

@FXML
public void buttonPressed(ActionEvent event) {
    Button button = (Button) event.getSource();
    // ...
}

answered Feb 2, 2015 at 21:31

James_D

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2 Comments

JonnyH Over a year ago

Thank you, I was able to achieve my desired result :D I used the following:

public void buttonPressed(ActionEvent event) { 		Object source = event.getSource(); 		((Labeled) source).setText("1"); 	}

The (Labeled) was an auto-generated fix that Eclipse put in though, and isn't something I've seen before. Do you know if this is a problem/bad practice?

James_D Over a year ago

I dislike downcasts generally. They are somewhat prone to runtime errors: for example if at a later date you registered your listener with something that wasn't a Labeled (e.g. a MenuItem) then your code would compile but you'd get runtime errors. Here it's probably an ok thing to do; if you're registering the button handler in FXML and you have many buttons it's your only option other than having one method for every button.

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