JavaFX: what is the difference between EventHandler and EventFilter?

Question

I've been googling for a while and I found that basicly, some web pages says there are no big differences. Except for some points:

1. EventFilter is executed before EventHandler

2. EventFilter is not sensible to event.Consume(); Let me see If I've understood it: Lets say I have:

   Button b= new Button("Test"); b.addEventHandler(.....){...}; b.addEventFilter(......){...};

Let's say they are both "linked" to an MouseEvent.MOUSE_CLICKED; then, EventFilter's code will be the first to be executed!?

Let's say, now, I have:

Button b= new Button("Test"); b.addEventHandler(.....); b.addEventFilter(......){   //some code   event.consume(); }; // First filter b.addEventFilter(......){   //some other code   event.consume(); }; // Second filter 

In this case, boath EventFilters will be executed but the EventHandler will not. Right?

Are there any other things to know? Are there situations where I should prefere one or other? should I sometimes use them together in order to solve some problems?

Thank you!

Answer 1

Whenever an event happens, it follows a process to determine which node in the scene graph should handle the event. The process takes these steps:

• Target selection
• Route construction
• Event capturing <- filters are triggered here
• Event bubbling <- handlers are triggered here

Target Selection Say that your scene contains a pane with a circle. If you click on the circle, the circle becomes the event target.

Route Construction Next, JavaFX creates a route (or an event dispatch chain). In our example the chain would look like stage -> scene -> pane -> circle

Event Capturing The event gets carried through every event filter on the chain. As soon as one of the filters calls consume(), the chain stops and that node becomes the target. If no filter calls consume() the end of the chain (the circle) remains the target.

Event Bubbling Next, the event get pushed through the chain again, but this time from the event target to the stage. So if the pane event filter called consume(), the following event handlers will be hit: pane -> scene -> stage

So the difference is not only when these handlers get activated, but also that event filters can prevent child nodes from receiving events.

Answer 2

As I know JavaFX EventFilter can be one or many for a single node and can be single for many nodes. EventFilter enable you to handle an event during the event capturing phase but the event handler handle events during the event bubbling phase.

So EventFilter is executed before the EventHandler.

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