Thank you for your time, the blog is fantastic – full of useful hints and inspiration.

Regards.

Excellent question. I don’t think users can resize columns if there isn’t a visible header.
One workaround is to enable the headers when the user rolls over the DataGrid control, as seen in the following example:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">

    <mx:Array id="arrDP">
        <mx:Object c="1" c1="One" c2="Two" c3="Three" />
        <mx:Object c="2" c1="One" c2="Two" c3="Three" />
        <mx:Object c="3" c1="One" c2="Two" c3="Three" />
        <mx:Object c="4" c1="One" c2="Two" c3="Three" />
        <mx:Object c="5" c1="One" c2="Two" c3="Three" />
        <mx:Object c="6" c1="One" c2="Two" c3="Three" />
        <mx:Object c="7" c1="One" c2="Two" c3="Three" />
        <mx:Object c="8" c1="One" c2="Two" c3="Three" />
        <mx:Object c="9" c1="One" c2="Two" c3="Three" />
        <mx:Object c="10" c1="One" c2="Two" c3="Three" />
        <mx:Object c="11" c1="One" c2="Two" c3="Three" />
    </mx:Array>

    <mx:DataGrid id="dataGrid"
            dataProvider="{arrDP}"
            showHeaders="false"
            rollOver="dataGrid.showHeaders = true;"
            rollOut="dataGrid.showHeaders = false;" />

</mx:Application>

The other workaround would be to always show the data grid headers, but set the headerHeight property to a small value (such as 2-4). This would still allow users to resize columns, but it wouldn’t display column labels. The only catch is that the sort arrow would still appear, so you would either need to set the sortableColumns property to false, or create a transparent icon for the sort arrow (setting the sortArrowSkin style to null was problematic).

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">

    <mx:Array id="arrDP">
        <mx:Object c="1" c1="One" c2="Two" c3="Three" />
        <mx:Object c="2" c1="One" c2="Two" c3="Three" />
        <mx:Object c="3" c1="One" c2="Two" c3="Three" />
        <mx:Object c="4" c1="One" c2="Two" c3="Three" />
        <mx:Object c="5" c1="One" c2="Two" c3="Three" />
        <mx:Object c="6" c1="One" c2="Two" c3="Three" />
        <mx:Object c="7" c1="One" c2="Two" c3="Three" />
        <mx:Object c="8" c1="One" c2="Two" c3="Three" />
        <mx:Object c="9" c1="One" c2="Two" c3="Three" />
        <mx:Object c="10" c1="One" c2="Two" c3="Three" />
        <mx:Object c="11" c1="One" c2="Two" c3="Three" />
    </mx:Array>

    <mx:DataGrid id="dataGrid"
            dataProvider="{arrDP}"
            headerHeight="4"
            sortableColumns="false" />

</mx:Application>

Hope that helps,

Peter