JavaFX UI在事件侦听器的JavaFX应用程序线程中冻结，但可与Platform.runLater一起使用

Question

In my JavaFX program, I currently have all my code running on the JavaFX Application Thread (including game logic code that does not necessarily update the UI). I've read that you should run non-UI code in a separate background thread and then update it accordingly in the JavaFX Application Thread using Platform.runLater or Tasks , so that the UI is not blocked, but I'm still confused as to why the UI freezes when I simply call myFlowPane.getChildren().remove() on the JavaFX Application Thread.

The following code hopefully provides enough context

hand.getTiles().addListener((ListChangeListener<ObservableTile>) change -> {
    while (change.next()) {
        if (change.wasAdded()) {
            for (Tile t : change.getAddedSubList()) {
                var btn = tileButtonFactory.newTileButton(t);
                fpHand.getChildren().add(change.getFrom(), btn);
            }
        } else if (change.wasRemoved()) {
            // Player can only remove 1 tile at a time
            Tile tile = change.getRemoved().get(0);
            fpHand.getChildren().removeIf(node -> ((TileButton)node).getTile().equals(tile));
        }
    }
});

I have a FlowPane that contains a bunch of buttons, and I'm listening on an ObservableList that contains a bunch of tiles. When this list of tiles changes, I want to update the FlowPane accordingly so that any new tiles, I create a button in the FlowPane. Similarly, when a tile is removed from this list of tiles, I want the button that contains this Tile to be removed from the FlowPane.

So from what I found online, event listeners run on the JavaFX Application Thread. This means that the code above is running on the JavaFX Application thread. When I add a button to my FlowPane, the UI does not freeze/get blocked fpHand.getChildren().add() . On the other hand, when I remove a button from the FlowPane, the UI freezes on fpHand.getChildren.remove .

However, when I wrap the fpHand.getChildren.remove() call with a Platform.runLater() , the UI is responsive and doesn't freeze. Why is this? All the code is currently running on the JavaFX Application Thread.

Also, I have a similar problem with another part of my code. I have a GridPane with 128 cells (which each cell has an HBox) and I need to update the table. I have the following code:

private void updateTable() {
    Platform.runLater(() -> {
        clearTable();
        table.forEach(this::addTilesToTable);
    });
}
private void clearTable() {
    for (int row = 0; row < gpTable.getRowCount(); row++) {
        for (int col = 0; col < gpTable.getColumnCount(); col++) {
            getCellFromGridPane(row, col).ifPresent(hbox -> hbox.getChildren().clear());
        }
    }
}

If I remove the Platform.runLater() , the UI doesn't freeze completely, but any tiles I've added previously in the spot, it's as if there's an invisible tile there on the table, and hence I cannot add a tile there, even though it should be empty. The updateTable() function is also called in the JavaFX Application Thread, and in an event listener. It seems as if the hbox.getChildren.clear() isn't being called properly if I remove Platform.runLater() .

Answer 1

The problem I had was that I was using setMouseTransparent(true) for the root panes that hold the buttons containing the Tile for click and drag and not consume mouse events.

    node.addEventHandler(MouseEvent.MOUSE_PRESSED, e -> {
        root.setMouseTransparent(true);
        dragContext.setMouseX(e.getSceneX());
        dragContext.setMouseY(e.getSceneY());
        dragContext.setInitialTranslateX(node.getTranslateX());
        dragContext.setInitialTranslateY(node.getTranslateY());
        e.consume();
    });

And when you release the mouse, it sets it back to false

    node.addEventHandler(MouseEvent.MOUSE_RELEASED, e -> {
        root.setMouseTransparent(false);
        node.setTranslateX(0);
        node.setTranslateY(0);
        e.consume();
    });

The problem here was that when I remove the button from the scene, it destroys all event handlers, and even though i release the mouse, it doesn't run this code.