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dataGrid控件的showHeaders和headerHeight属性。
示例：

代码：

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/06/16/setting-the-header-height-on-a-datagrid-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            private function init():void {
                slider.value = dataGrid.headerHeight;
            }
        ]]>
    </mx:Script>

    <mx:Array id="arr">
        <mx:Object col1="1.One" col2="1.Two" />
        <mx:Object col1="1.One" col2="1.Two" />
        <mx:Object col1="1.One" col2="1.Two" />
        <mx:Object col1="1.One" col2="1.Two" />
        <mx:Object col1="1.One" col2="1.Two" />
    </mx:Array>

    <mx:ApplicationControlBar dock="true">
        <mx:Form styleName="plain">
            <mx:FormItem label="headerHeight:">
                <mx:HSlider id="slider"
                        minimum="0"
                        maximum="40"
                        snapInterval="1"
                        liveDragging="true" />
            </mx:FormItem>
            <mx:FormItem label="showHeaders:">
                <mx:CheckBox id="checkBox"
                        selected="true" />
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:DataGrid id="dataGrid"
            dataProvider="{arr}"
            headerHeight="{slider.value}"
            showHeaders="{checkBox.selected}"
            initialize="init();">
        <mx:columns>
            <mx:DataGridColumn dataField="col1" />
            <mx:DataGridColumn dataField="col2" />
        </mx:columns>
    </mx:DataGrid>

</mx:Application>

也可以通过AS实现：

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/06/16/setting-the-header-height-on-a-datagrid-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.events.SliderEvent;

            private function init():void {
                slider.value = dataGrid.headerHeight;
            }

            private function slider_change(evt:SliderEvent):void {
                dataGrid.headerHeight = evt.value;
            }
        ]]>
    </mx:Script>

    <mx:Array id="arr">
        <mx:Object col1="1.One" col2="1.Two" />
        <mx:Object col1="1.One" col2="1.Two" />
        <mx:Object col1="1.One" col2="1.Two" />
        <mx:Object col1="1.One" col2="1.Two" />
        <mx:Object col1="1.One" col2="1.Two" />
    </mx:Array>

    <mx:ApplicationControlBar dock="true">
        <mx:Form styleName="plain">
            <mx:FormItem label="headerHeight:">
                <mx:HSlider id="slider"
                        minimum="0"
                        maximum="40"
                        snapInterval="1"
                        liveDragging="true"
                        change="slider_change(event);" />
            </mx:FormItem>
            <mx:FormItem label="showHeaders:">
                <mx:CheckBox id="checkBox"
                        selected="true" />
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:DataGrid id="dataGrid"
            dataProvider="{arr}"
            showHeaders="{checkBox.selected}"
            initialize="init();">
        <mx:columns>
            <mx:DataGridColumn dataField="col1" />
            <mx:DataGridColumn dataField="col2" />
        </mx:columns>
    </mx:DataGrid>

</mx:Application>