JavaFX TableView Selection Binding doesn't always fire - is there a better work around? - binding

Question

I have the need to disable a button in my application provided nothing is selected or multiple rows are selected.
I created the following binding (extra code to debug it since it wasn't working)..
BooleanBinding singleDocIsntSelected =
Bindings.createBooleanBinding(() -> {
boolean result = documentTable.getSelectionModel().getSelectedItems().size() != 1;
return result;
}, documentTable.getSelectionModel().selectedItemProperty());
What happens to me is that when I select the first row, it fires, then if I CTRL + Click the same row, it fires again. So far all is well in the world. Then I Click the same row - nothing, or when I CTRL Click other rows nothing.
My button will stay in the wrong state.
However, if I also add a listener to the property:
ChangeListener<MyDTO> selectedItemsListener = (obs, ov, nv) -> {
boolean result = table.getSelectionModel().getSelectedItems().size() != 1;
System.err.println(result);
};
Then everything works properly.
Is there no other way to handle this?

Answer 1

You need the binding to be invalidated when the list of selected items changes, not when the selectedItem property changes. If one item is selected, that becomes the selected item: if you then select additional items, the selectedItemProperty will not change (it is still the first one selected out of all those selected).
Using your current idiom, just bind to the selected items list:
BooleanBinding singleDocIsntSelected =
Bindings.createBooleanBinding(() -> {
boolean result = documentTable.getSelectionModel().getSelectedItems().size() != 1;
return result;
}, documentTable.getSelectionModel().getSelectedItems());
or, more simply,
BooleanBinding singleDocIsntSelected =
Bindings.createBooleanBinding(
() -> documentTable.getSelectionModel().getSelectedItems().size() != 1,
documentTable.getSelectionModel().getSelectedItems());
Though it's probably cleaner to use Bindings.size() and IntegerBinding.isNotEqualTo():
BooleanBinding singleDocIsntSelected = Bindings
.size(documentTable.getSelectionModel().getSelectedItems())
.isNotEqualTo(1);