ComboBox item height bug

[John Hendrikx]

What you are likely seeing is that the minimum always wins over the
other values.

The minimum height is set to the constant USE_PREF_SIZE, which means
that it will take the preferred size for the minimum height.

When it comes to size priorities (min, pref and max), minimum always
wins, then comes maximum, then comes preferred.

So in this case, the preferred size is say 20.  The minimum follows the
preferred, also 20.  You set maximum to 1.  Minimum > Maximum, so
Maximum is ignored.

What you could try is set preferred size smaller instead; there should
be no need to change minimum or maximum then.

--John

On 08/11/2025 21:30, Cormac Redmond wrote:
> Hi,
>
> I have found a height bug when I am trying to reduce the height of one
> ComboBox item (a Separator) in a simple ComboBox.
>
> One would expect that to achieve this, you'd set the maximum height
> for that particular ListCell; but this has no effect.
>
> Instead what I need to do is set the /minimum/ height (but to the
> value I wish to be the maximum height), and I must *also *set the
> /maximum /height to any value (if I do not, my minimum height (i.e.,
> my desired maximum) gets ignored)...
>
> For example, if I want the maximum height of this Separator to be 6, I
> must set the minimum height to 6 and I must set the maximum height to
> anything, even 1.
>
> Obviously this is counter-intuitive and doesn't make any logical sense.
>
> Example to reproduce (running from JFX master branch):
>
> public class ComboBoxHeightBug extends Application {
>     public static void main(String[] args) {
>         launch(args);
>     }
>
>     public void start(Stage stage) {
>         ComboBox<Object> cb = new ComboBox<>();
>         cb.getItems().addAll("Apple", "Banana",  new Separator() ,
> "Carrot", "Lettuce");
>         cb.setCellFactory(_ -> new ListCell<>() {
>             protected void updateItem(Object item, boolean empty) {
>                 super.updateItem(item, empty);
>                 if (empty || item == null) {
>                     setText(null);
>                     setGraphic(null);
>                     setStyle("");
>                     // Set back to default
>                     setMinHeight(USE_PREF_SIZE);
>                     setMaxHeight(Double.MAX_VALUE);
>                 } else if (item instanceof Separator) {
>                     setText(null);
>                     setGraphic((Separator) item);
>                     setDisable(true);
>                     setMinHeight(6); // This is required for any "max
> height" to apply, and appears to be the value that is used to
> determine height
>                     setMaxHeight(1); // Setting this (to 6) should
> work on its own, it doesn't, the value appears irrelevant -- but it
> MUST be set to get the separator height to be 6
>                 } else {
>                     setText(item.toString());
>                     setGraphic(null);
>                     setStyle("");
>                     // Set back to default
>                     setMinHeight(USE_PREF_SIZE);
>                     setMaxHeight(Double.MAX_VALUE);
>                 }
>             }
>         });
>
>         cb.getSelectionModel().selectFirst();
>         stage.setScene(new Scene(cb, 200, 100));
>         stage.show();
>     }
> }
>
> Note: I have noticed a few issues like this in general, whereby it
> requires trial and error to get /some/ desired height to apply;
> without any apparent logic as to how these values are being arrived at
> or how they're triggered to be used (I have logged bugs before on this)...
>
>
> Kind Regards,
> Cormac
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