Flex ComboBox subclass with "Null" / "All" option?

Just wondering if anybody knows of an existing component that subclasses ComboBox but lets you specify an item in the list with a label like "all" or "none" that will set selectedItem to null? I've looked into writing one, and due to the internals of the component it looks like a lot of work, so I'm wondering if some开发者_高级运维body's already done it?

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What would a ComboBox look like when no item is selected? Or all items selected for that matter? It sounds like you should use a List instead of a ComboBox. Look at the list controls on Tour de Flex.

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How about something like this.

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Run this:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" width="100%" height="100%" creationComplete="onCreationComplete()">
    <mx:Script>
        <![CDATA[
            private var myData:Array = new Array();

            [Bindable]
            private var comboData:Array = new Array();

            [Bindable]
            private var selectedData:String = "";

            private function onCreationComplete():void
            {
                myData.push({"label" : "First", "value" : "First"});
                myData.push({"label" : "Second", "value" : "Second"});
                myData.push({"label" : "Third", "value" : "Third"});

                comboData.push({"label" : "<None>", "value" : "<None>"});
                comboData.push({"label" : "<All>", "value" : "<All>"});
                for(var i:int = 0; i < myData.length; i++) {
                    comboData.push(myData[i]);
                }
            }

            private function onSmartComboBoxChange():void
            {
                if(smartComboBox.selectedItem) {
                    if(smartComboBox.selectedItem.value == "<None>") {
                        selectedData = "";
                    } else if(smartComboBox.selectedItem.value == "<All>") {
                        selectedData = "";
                        for(var i:int = 0; i < myData.length; i++) {
                            selectedData += myData[i].value + ", ";
                        }
                    } else {
                        selectedData = comboData[smartComboBox.selectedIndex].value;
                    }
                }
            }
        ]]>
    </mx:Script>
    <mx:VBox>
        <mx:ComboBox id="smartComboBox" dataProvider="{comboData}" change="onSmartComboBoxChange()" labelField="label" />
        <mx:Label id="selectedDataLabel" text="{selectedData}" />
    </mx:VBox>
</mx:Application>