Full code after the jump.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/01/04/changing-a-box-containers-direction-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Style>
        .myBox {
            paddingLeft: 10;
            paddingRight: 10;
            paddingTop: 10;
            paddingBottom: 10;
            backgroundColor: haloSilver;
        }
    </mx:Style>

    <mx:Script>
        <![CDATA[
            import mx.events.ListEvent;
            import mx.containers.BoxDirection;

            private function comboBox_init():void {
                var arr:Array = [];
                arr.push({label:BoxDirection.HORIZONTAL});
                arr.push({label:BoxDirection.VERTICAL});
                comboBox.dataProvider = arr;
            }

            private function comboBox_change(evt:ListEvent):void {
                box.direction = comboBox.selectedLabel;
            }
        ]]>
    </mx:Script>

    <mx:ApplicationControlBar dock="true">
        <mx:Form styleName="plain">
            <mx:FormItem label="direction:">
                <mx:ComboBox id="comboBox"
                        initialize="comboBox_init();"
                        change="comboBox_change(event);" />
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:Box id="box" direction="horizontal" styleName="myBox">
        <mx:Image source="Button.png" toolTip="Button" />
        <mx:Image source="ButtonBar.png" toolTip="ButtonBar" />
        <mx:Image source="CheckBox.png" toolTip="CheckBox" />
        <mx:Image source="ColorPicker.png" toolTip="ColorPicker" />
        <mx:Image source="ComboBox.png" toolTip="ComboBox" />
    </mx:Box>

</mx:Application>

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