有没有办法检查ComboBox在JavaFX中是否有任何项目？

Question

Is there a way to check if a ComboBox has any items in it or whether it is empty? I have an array of ComboBox es and I need to go through each of them, if there are no items in the ComboBox , then I must hide it. This following code doesn't seem to work:

for (ComboBox cmb : comboBoxes) {
    if (cmb.getItems().isEmpty()) {
        cmb.hide();
    }
}

Answer 1

The code for checking, if the ComboBox has no items is correct, you code for hiding the ComboBox es is incorrect however.

ComboBox.hide only closes the popup showing the items, if it's open. It does not hide the ComboBox . To hide the ComboBox , you need to set the visibility:

for (ComboBox cmb : comboBoxes) {
    if (cmb.getItems().isEmpty()) {
        cmb.setVisible(false);
    }
}

Answer 2

Alternatively to call a method to hide the ComboBox es, you can bind the visibleProperty of the ComboBox es to their own itemsProperty with a custom binding:

List<ComboBox<String>> comboBoxes = new ArrayList<>();
for(int i = 0; i< 10; i++) {
    ComboBox<String> combo = new ComboBox<>();
    combo.visibleProperty().bind(Bindings.createBooleanBinding(() -> !combo.getItems().isEmpty(),
        combo.itemsProperty().get()));
    comboBoxes.add(combo);
}

The advantage is, that you don't have to call any methods to hide your ComboBox es, because the binding is evaluated automatically, therefore no one can see your empty combos.

Answer 3

The .getItems() method returns an ObservableList<T> so you can just check its .size() . This will tell you if it's empty.

for (ComboBox cmb : comboBoxes) {
  if (cmb.getItems().size() <= 0) { // or cmb.getItems().isEmpty()
      cmb.setVisible(false); }
}

If the ComboBox is populated by a List of its own, you could also just check if the list is empty with the same .size() call.