Selection highlighting in List doesn't disapear after intercepting value commit event

Question

I am using a spark List and wanted to maintain the selection after changing the content of the list that is the data provider. If you set a new data provider the List sets its selectedIndex back to -1. We solved this problem by intercepting the valueCommit event that is fired when teh List wants to set itself back to -1 and setting the previously selected item (if the new data provider still contains it). This works so far but we are getting strange behaviour:

initially the previously selected item is still selected and highlighted as intended
if another item is selected, the highlighting stays on the intial item. It doesn't matter how often I select another one, the initial item is still highlighted but not selected. The newly selected item is in fact selected and also highlighted.
if the initial item is selected again the List is behaving normal again. When I select another item after I reselected the initial one once, the highlighting disapears.

The List is declared in an MXML like this:

<s:List dataProvider="{model.dataProvider}"
selectedIndex="@{model.selectedIndex}"
valueCommit="model.handleInputObjectListValueCommit(event)"/>

The code in the model class is very complex but this should be the relevant part:

[Bindable]
public var dataProvider:ArrayCollection;

[Bindable]
public var selectedIndex:int;

private var _indexToSelect:int = -1;

public function setNewContent(newContent:ArrayCollection):void {

    undoManager.ignore(function ():void {

        dataProvider.removeAll();
        dataProvider.addAll(newContent);

        _indexToSelect = selectedIndex;
    });
}

public function handleValueCommit(event:Event):void {
    if (_indexToSelect != -1) {
        const localIndex:int = _indexToSelect;
        _indexToSelect = -1;
        selectedIndex = localIndex;
    }
}

The undManager is a class that takes care of undo/redo. The ignore function takes care that the undoManager doesn't register the change in the dataProvider as an undoable action because only user interaction should be undoable.

any ideas?

Thanks for all your answers. Looks like I'm not getting around posting some code. I will do this later because it could take some time to simplify it for posting. — André Stannek
Just noticed my initial question was not entirely correct. I am not setting a new data provider, I am empting the existing one and refilling it. Must have confused it with another problem I had. Sorry for that! — André Stannek

CheeseWarlock CheeseWarlock · Accepted Answer · 2012-05-18T14:58:11

I got the described result when capturing change events, and fixing it there would require either a hackish solution or a custom UI component to fix what seems like a bug in the List component. But it seems to work if you handle the logic as you change the data provider rather than trying to capture events:

public function setDataProvider(data:IList):void {
    var previous:Object = theSparkList.selectedItem;
    theSparkList.dataProvider = data;
    var index:int = theSparkList.dataProvider.getItemIndex(previous);
    if (index > -1) {
        theSparkList.selectedIndex = index;
    }
}

This might still require some refactoring, and it might not work with your architecture- you might have to provide more detail on that. Is capturing events the only choice?

Selection highlighting in List doesn't disapear after intercepting value commit event

3 Answers