<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/08/04/creating-two-related-comboboxes/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white" viewSourceURL="srcview/index.html">

    <mx:XML id="dp" source="countries_states_cities.xml" format="e4x" />

    <mx:Form>
        <mx:FormItem label="Country:">
            <mx:ComboBox id="countryCB"
                    dataProvider="{dp.country}"
                    labelField="@name" />
        </mx:FormItem>
        <mx:FormItem label="State:">
            <mx:ComboBox id="stateCB"
                    dataProvider="{countryCB.selectedItem.state}"
                    labelField="@name" />
        </mx:FormItem>
        <mx:FormItem label="City:">
            <mx:ComboBox id="cityCB"
                    dataProvider="{stateCB.selectedItem.city}"
                    labelField="@name" />
        </mx:FormItem>
    </mx:Form>

</mx:Application>