javafx have an eventfilter remove itself - javafx

Question

A snippet of my code is as follows:
//button clicked method
#FXML
public void newHeatExchanger2ButtonClicked(ActionEvent event) throws Exception {
//new pane created
Pane pane = new Pane();
//method call everytime the button is clicked
create2DExchanger(pane);
}
//method declaration
private void create2DExchanger(Pane pane) {
EventHandler<MouseEvent> panePressed = (e -> {
if (e.getButton() == MouseButton.SECONDARY){
do stuff
}
if (e.getButton() == MouseButton.PRIMARY){
do stuff
}
});
EventHandler<MouseEvent> paneDragged = (e -> {
if (e.getButton() == MouseButton.PRIMARY){
do stuff
}
});
EventHandler<MouseEvent> paneReleased = (e -> {
if (e.getButton() == MouseButton.PRIMARY){
do stuff;
}
});
EventHandler<MouseEvent> paneMoved = (t -> {
do stuff;
});
EventHandler<MouseEvent> paneClicked = (t -> {
//I need this filter to remove itself right here
t.consume();
pane.removeEventFilter(MouseEvent.MOUSE_MOVED, paneMoved);
pane.addEventHandler(MouseEvent.MOUSE_PRESSED, panePressed);
pane.addEventHandler(MouseEvent.MOUSE_DRAGGED, paneDragged);
pane.addEventHandler(MouseEvent.MOUSE_RELEASED, paneReleased);
});
pane.removeEventHandler(MouseEvent.MOUSE_PRESSED, panePressed);
pane.removeEventHandler(MouseEvent.MOUSE_DRAGGED, paneDragged);
pane.removeEventHandler(MouseEvent.MOUSE_RELEASED, paneReleased);
pane.addEventFilter(MouseEvent.MOUSE_MOVED, paneMoved);
pane.addEventFilter(MouseEvent.MOUSE_PRESSED, paneClicked);
}
Initially I set the pane to have only the event filters of mouse_moved, and mouse_pressed. As soon as the mouse is clicked I need the mouse filter for mouse_pressed and mouse_moved to go away and add the eventHandlers as I do in the paneClicked filter llamda. I need the first set of events to be filters because there are children nodes I do not want to receive the event (i.e. an event filter on an arc that is a child of the pane). The second set need to be handlers because the arc event filter needs to consume the event before the pane eventHandlers receive it.
Convenience events like:
pane.setOnMousePressed()
can remove themselves by calling
pane.setOnMousePressed(null);
but I need this initial event filter to remove itself. I will need the functionality of an event removing itself later as well in the code, but if I try to add
pane.removeEventFilter(MouseEvent.MOUSE_PRESSED, paneClicked);
to
EventHandler<MouseEvent> paneClicked = (t -> {
//I need this filter to remove itself right here
t.consume();
pane.removeEventFilter(MouseEvent.MOUSE_MOVED, paneMoved);
pane.addEventHandler(MouseEvent.MOUSE_PRESSED, panePressed);
pane.addEventHandler(MouseEvent.MOUSE_DRAGGED, paneDragged);
pane.addEventHandler(MouseEvent.MOUSE_RELEASED, paneReleased);
});
It will not compile. I have been researching for a couple of days on how to get the functionality of an eventFilter or eventHandler to remove itself but I am coming up short. I have not found anything online or on stackexchange in my Google searches either. I would really appreciate being able to figure this thing out. Thanks.

Answer 1

I believe the problem stems from the fact that you try to access paneClicked before it was fully declared.
You can overcome this using an anonymous class with the this keyword:
EventHandler<MouseEvent> paneClicked = new EventHandler<MouseEvent>() {
#Override
public void handle(MouseEvent event) {
event.consume();
pane.removeEventFilter(MouseEvent.MOUSE_PRESSED, this);
pane.removeEventFilter(MouseEvent.MOUSE_MOVED, paneMoved);
pane.addEventHandler(MouseEvent.MOUSE_PRESSED, panePressed);
pane.addEventHandler(MouseEvent.MOUSE_DRAGGED, paneDragged);
pane.addEventHandler(MouseEvent.MOUSE_RELEASED, paneReleased);
}
};
Or by referencing a fully qualified static function:
public class ContainingClass {
...
private static EventHandler<MouseEvent> paneClicked = (t -> {
t.consume();
pane.removeEventFilter(
MouseEvent.MOUSE_PRESSED, ContainingClass.paneClicked
);
});
}
See also:
Why do lambdas in Java 8 disallow forward reference to member variables where anonymous classes don't?
Java8 Lambdas vs Anonymous classes