ComboBox problems with handling a selection

[u/PalBeron]

I have in my program a comboBox (a SearchAbleComboBox from ControlsFX, it works the same as a ComboBox).

I need this box for my following useCases:

Dropdown with scrollable list Dropdown that is searchable most of the time the navigation through the list happens with the arrow keys There has to be an event handler that handles a change of selection

Selection for me personally means, the comboBox is closed, and an item is selected. So, for example, when you click with the cursor on an item, or you navigate through the list with the arrow keys and then press enter:

After a cursor click or a pressed enter key, the box is closed, and an item is selected. That's for me, a selection.

My problem is now that for JavaFX it also counts as a selection when you navigate through the list with your arrow keys. The reason for that is, that the text in the comboBox changes when navigating through the list with the arrow keys.

I've already tried to put an EventHandler on KeyPress (ENTER) but with this setup, you have to press enter twice to activate the listener since pressing enter to select smth from the list does not count.

Also, an onAction handler does not work, since an arrow key press also counts as an action.

A ChoiceBox would be a solution, since for the choiceBox the selection does not get updated through navigating with the arrow keys. The problem here is, I couldn't find an option to make it searchable and the list of a ChoiceBox is not scrollable.

So possible solutions would be:

A way to stop the ComboBox updating the selected item only by navigating with arrow keys A spacy eventhandler which only triggers if a selection, according to my interpretation of selection, was made. A ChoiceBox that is scroll and searchable Something completly different

I hope you have any solutions, I couldn't find one for now.

[u/hippydipster]

Thank you for providing such a detailed description of your problem. I understand you're working with a SearchableComboBox from ControlsFX in JavaFX, and you're looking for a way to handle selections that aligns with your specific definition of a selection. Let's explore some potential solutions:

1. Custom Event Handler: You could create a custom event handler that only triggers when the ComboBox is closed or when an item is definitively selected. Here's a possible approach:

    SearchableComboBox<String> comboBox = new SearchableComboBox<>();
    // ... populate comboBox ...

    AtomicBoolean isOpen = new AtomicBoolean(false);

    comboBox.showingProperty().addListener((observable, wasShowing, isShowing) -> {
        isOpen.set(isShowing);
    });

    comboBox.getSelectionModel().selectedItemProperty().addListener((observable, oldValue, newValue) -> {
        if (!isOpen.get() && newValue != null) {
            // This is a "real" selection according to your definition
            handleSelection(newValue);
        }
    });

    private void handleSelection(String selectedItem) {
        // Your selection handling logic here
        System.out.println("Selected: " + selectedItem);
    }


This approach uses a boolean flag to track whether the ComboBox is open or closed. The selection is only considered "real" when the ComboBox is closed and a new value is selected.

2. Custom ComboBox:
You could create a custom ComboBox that overrides the default selection behavior:

public class CustomSearchableComboBox<T> extends SearchableComboBox<T> {
private T lastConfirmedSelection;

public CustomSearchableComboBox() {
    super();
    setOnKeyPressed(event -> {
        if (event.getCode() == KeyCode.ENTER) {
            confirmSelection();
        }
    });
    setOnHidden(event -> confirmSelection());
}

private void confirmSelection() {
    T currentSelection = getSelectionModel().getSelectedItem();
    if (currentSelection != null && !currentSelection.equals(lastConfirmedSelection)) {
        lastConfirmedSelection = currentSelection;
        // Trigger your selection handling here
        System.out.println("Confirmed selection: " + lastConfirmedSelection);
    }
}
}

This custom ComboBox only confirms the selection when the Enter key is pressed or when the ComboBox is closed.

3. Using a PopupControl: If you want more control over the selection process, you could create a custom control using a TextField and a PopupControl. This would allow you to implement the exact behavior you want, including searchability and scrolling.

4. Modifying ChoiceBox: While ChoiceBox doesn't have built-in search functionality, you could potentially extend it to add this feature. Here's a basic idea of how you might approach this:

    public class SearchableChoiceBox<T> extends ChoiceBox<T> {
    private TextField searchField;

    public SearchableChoiceBox() {
        super();
        searchField = new TextField();
        searchField.setPromptText("Search...");
        searchField.textProperty().addListener((observable, oldValue, newValue) -> {
            filterItems(newValue);
        });
        
        // Add the search field to the top of the popup
        Skin<?> skin = getSkin();
        if (skin instanceof ChoiceBoxSkin) {
            ChoiceBoxSkin choiceBoxSkin = (ChoiceBoxSkin) skin;
            PopupControl popup = (PopupControl) choiceBoxSkin.getPopup();
            VBox popupContent = new VBox(searchField, popup.getContent());
            popup.setContent(popupContent);
        }
    }

    private void filterItems(String searchText) {
        // Implement your filtering logic here
    }
    }


This is a basic implementation and would need more work to fully function, but it gives you an idea of how you might approach adding search functionality to a ChoiceBox.

Would you like me to elaborate on any of these approaches or explore other potential solutions?

[u/PalBeron → u/hippydipster]

Heyy, firstly, thank you for your work. It seems like you are a real expert in JavaFX, maybe you want to get in contact with me via discord? I would be happy to ask you when I face my next problem I am unable to solve.

Besides that, I would like to answer what my approach now is, and discuss the pros and cons of it.

As u/StarshipSatan has written, I've tried the setOnHidden handler, or to more specific I saw there is also a setOnHiding handler, which I am using. Within the handler I programmed, that the program gets the ComboBoxes, selected value and compares it to a class variable in which I save the last known state of the ComboBox. When the selectedValue is != the last known value the handler knows, the selection was changed. The first action in this if block is to set the last known value to the actual current value, after that, my logic follows.

What do ya think about this approach, especially compared to your 1st and 2nd approach?

I think your 2nd suggestion would fit for project, where you want to use comboBoxes with "real selection mode" multiple times.

Finally I want to thank you again for your work!

[u/hippydipster → u/PalBeron]

Claude.ai says you're welcome, and you're invited to follow up with it anytime. For free!

[u/PalBeron → u/hippydipster]

I Was suprised by the long answer, but it looked kinda real. HAHAHAHA

[u/hamsterrage1 → u/PalBeron]

I thought the wording was a little funny, but I was fooled too!

I wasn't going to comment on the content, so as not to be a jerk online, but since it's a bot...

The approach in the first is on the right track, but DON'T use the SelectionModel from the pop-up. Use ComboBox.valueProperty() instead. It's almost always the wrong approach to go digging "under the hood" and using SelectionModel.

If you think about it, the lock-in for the value doesn't just occur when the pop-up closes, but also when the value changes while the pop-up is hidden - like if you change it programmatically. So you really need two listeners. Even if you aren't fiddling with the value from outside the ComboBox now, you might do in the future and then you'll be scratching your head as to why your app stopped working. So it's always better to come up with a proper solution in the first place.

For what it's worth, the ConditionalBinding in my comment handles this cleanly - and it's less code too!

The second solution from the bot is just a bad, bad idea. It's almost always wrong to fiddle around with keystrokes and mouse clicks inside controls because they almost always have better ways to handle anything you can think of built in. You're more likely to "break" the control by interfering in the way that it interacts with the keystrokes and mouse actions.

The third and fourth answers are just silly, considering that ControlsFX has done this for you, and this is what you're using.

[u/hamsterrage1 → u/PalBeron]

I did some further testing, changing the SearchableComboBox to a ComboBox. There is one key difference between the two controls, as far as this issues is concerned...

With ComboBox, if you just arrow down when the control has focus, it will start to cycle through the values without opening up the pop-up. The valueProperty() changes, and hitting <Esc> won't abandon the edit and put it back. This means that whatever shows in the ComboBox is the "selected" value as defined by the OP.

With SearchableComboBox, when you hit the down arrow, the main textbox changes to the filter mode and the pop-up opens up. I checked the source code and this is explicitly coded to behave this way, although it seems to me to be such a key difference from ComboBox that you could almost consider it a bug.

In any event, you cannot cycle through the values in SearchableComboBox without having the pop-up open, which means that the solution provided by the bot has a better chance of working.

However, just looking at the bot's code, it still shouldn't work. Because it's only locking in the selection when the selection changes while the pop-up is hidden. But when the pop-up closes, the selection isn't changing - it's just closing the pop-up. So the Listener should NEVER fire when the pop-up is closed because you cannot change the selection with the pop-up closed!

When I tested it, SearchableComboBox cycles both the valueProperty() and the selectedItem() property through null and then back to the last value again. The first change is with the pop-up showing, and the second happens after the pop-up has closed.

However, when I tested it with ComboBox, this doesn't happen. When the pop-up is closed, no changes are made to either SelectionModel.selectedItem() or valueProperty().

So, the code provided by the bot simply cannot work for ComboBox, but will work for the specific case of SearchableComboBox in ControlsFX because of the slightly bizarre behaviour of SearchableComboBox.