How to pass paremeter with an event in javafx?

Question

I have this following example, where I want to pass my paremeter "text" together with my event (when my button "bla" is clicked). How can I do it?

  EventHandler<MouseEvent> handler = new EventHandler<MouseEvent>() {
        @Override
        public void handle(MouseEvent event) {
            System.out.println(text);
        }
    };

    public void test(){
    //...

    Text text = "123567";

    bla.setOnMousePressed(handler);

    //...
    }

Small question:

When I do have the following:

   object1.setOnMouseClicked( event -> {
        System.out.println("HELLO");
    });

   object2.setOnMouseClicked( event -> {
        System.out.println("HELLO");
    });

two objects, doing the same thing when "setOnMouseClicked" on them. is there any syntax to merge them?

Give me 5minutes, need to get to my computer, but your question shall be answered — JohnRW, Feb 12 '16 at 22:10

score 7 · Accepted Answer · edited Jul 10 '17 at 06:45

There is multiple ways you can go at it. If the parameter you want to pass along is part of the event source or target you can:

use getSource or getTarget
check the class of source or target
cast the source/target to that class
access parameters via the getters and setters of that class

However if the parameter has nothing to do with the event, you will have to write a custom event:

class CustomEvent extends Event {

    private String parameter;

    public static final EventType<CustomEvent> CUSTOM = new EventType(ANY, "CUSTOM");
    public CustomEvent(String parameter) {
        super(CustomEvent.CUSTOM);
        this.parameter = parameter;
    }

    public String getParameter() {
        return this.parameter;
    }

}

Now to use that event you will first have to fire it.

You can do this with

objectThatWillFireThisEvent.fireEvent(new CustomEvent("Get this parameter guys!"));

So you now fired an event with a parameter. Now to set the EventHandler simple add this to the class of the object that will fire the event:

public final void setOnCustomEvent(
        EventHandler<? super CustomEvent> value) {
    this.addEventHandler(CustomEvent.CUSTOM, value);
}

Now you can set the event handler:

objectThatWillFireTheEvent.setOnCustomEvent( event -> {
    System.out.println(event.getParameter());
});

Alternatively if want you can use the way to write event handlers that you posted in your question (if you don't want to use lambdas).

Or you can just call a function that you wrote, that should handle that parameter:

objectThatWillFireTheEvent.setOnCustomEvent( event -> myFunction(event.getParameter) );

I hope I didn't make any typos. But if something does not work or you have any more questions, don't hesitate to ask! :)

In addition to that I would advice you to google casting (if you do not know that already) and more on custom events (since my answer is only a starting point and if you want to do more crazy shit with custom events it's better to read up on that :D)

Edit: Is this what you meant in your comment?

Since comments will destroy layout and readability

String text = "This is text!";
Button button = new Button();
object.setOnMouseClicked( event -> {
    function1(text);
    function2(button);
});

Here you can find an answer with casting: http://stackoverflow.com/questions/23928132/javafx-eventhandler-pass-parameter — JohnRW, Feb 12 '16 at 23:32
If you wanted to avoid custom events at all costs, you COULD extend the class that fires your event with a custom parameter, setter and getter and use the event source / target method to get it again. However I would strongly advice against this, since parameters that are in concept not connected to a class should not be added to a class in implementation ;) — JohnRW, Feb 12 '16 at 23:34
thank you - another small question: when I do have two elements, let's say "text" and "button" - and I want to bind them the both function when "setOnMouseClick" is done... is there any syntax I can use instead of writing text.setOnMouseClicked(new EventHandler() {....} + button.setOnMouseClicked(new EventHandler() {...} - is there any easy way like saying text&button.setOnMouseClicked.... - because then I would not need the stuff above - I could say it shall do the same stuff for both elements, when onmouse.. is fired — user3650191, Feb 12 '16 at 23:48
No you have to set the event handler for both objects, however you can use the same method to handle those events with a lambda ( event -> methodx() ) — JohnRW, Feb 13 '16 at 00:01

score 0 · Answer 2 · 2019-06-21T09:21:50.720

If you're using setOnMousePressed() method, you can access the variable text directly using lambda expression:

bla.setOnMousePressed(event -> {
    System.out.println(text);
});

But if you're going to use the EventHandler interface anyway or if you're going to use bla.addEventHandler(); here's a better way to do it:

You see the idea is to create a Custom EventHandler through which we pass all the data we need as parameters i.e. text in our case.

To create a Custom EventHandler, create an abstract class that implements the EventHandler interface.

public abstract class CustomEventHandler implements EventHandler<Event>
{
    private String text;

    public CustomEventHandler(String text) {
        this.text = text;
    }

    public String getText() {
        return text;
    }
}

Now you can pass the variable text through the constructor:

Button bla = new Button("bla");

String text = "123567";

bla.setOnMousePressed(new CustomEventHandler(text) {

    @Override
    public void handle(Event event) {
        System.out.println(getText());
    }
});

Output when the bla button is pressed:

I hope this answers your question.
Please ask away anything if you don't understand! :)

How to pass paremeter with an event in javafx?

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