将JavaFx ListView的选择索引绑定到整数属性

Question

Is it possible to bind (one-way) a ListView's selection index or item to a property?

I can get a ReadOnlyIntegerProperty with this call, but it's a ReadOnlyProperty which does not have the bind methods you see in ObjectProperty , StringProperty , etc.

myListView.getSelectionModel().selectedIndexProperty()

How do I go about binding an Integer Property to my ListView's selected index property?

Answer 1

The API exposes the selectedIndex as a ReadOnlyProperty because it doesn't want to expose the bind method that is part of the Property API. The reason it doesn't want to expose the bind method is that the ListView needs to be able to set the property when the user clicks on it. If the bind method were part of the API, and the programmer called listView.getSelectionModel().selectedIndexProperty().bind(...) , then runtime errors would be generated whenever the user clicked on the list.

Because the bindBidirectional is also part of the Property API, but not the ReadOnlyProperty API, this means that you also cannot bidirectionally bind the selectedIndex .

You can achieve the same effect as bidirectional binding using two listeners:

IntegerProperty property = new SimpleIntegerProperty();
ListView<?> listView = new ListView<?>();

// change property when selection changes:
listView.getSelectionModel().selectedIndexProperty().addListener((obs, oldIndex, newIndex) ->
    property.set(newIndex.intValue()));

// change selection when property changes:
property.addListener((obs, oldValue, newValue) -> 
    listView.getSelectionModel().clearAndSelect(newValue.intValue())); 

If you just want to bind the selected item index to the property, you only need the second listener.

If you just want to bind the property to the selected item index, and you are not going to set the property by other means, then of course you can just bind the property:

IntegerProperty property = new SimpleIntegerProperty();
property.bind(listView.getSelectionModel().selectedIndexProperty());

(Though in this case, you could always just reference the selectedIndexProperty directly if your design allows.)

Answer 2

I can understnad not permitting biDirectionalBinding since it's read only, but how can i do one way binding?

Try:

IntegerProperty property = new SimpleIntegerProperty();
property.bind(myListView.getSelectionModel().selectedIndexProperty());