WPF DataGrid: Cancel the first row selection by default -

in datagrid first row becomes selected default. how can cancel this?

<window x:class="wpfapplication50.window7" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"      xmlns:dg="clr-namespace:microsoft.windows.controls;assembly=wpftoolkit"      title="window7" sizetocontent="widthandheight"> <window.resources>     <!--data-->     <xmldataprovider x:key="mydata" xpath="/info">         <x:xdata>             <info xmlns="">                 <item id="isbn 45-f1" name="winner" price="$32.05" author="aka" catalog="business"/>                 <item id="isbn 54-32" name="c++ inside" price="$10.00" author="john" catalog="language"/>                 <item id="isbn 14-a0" name="java inside" price="$9.00" author="tom" catalog="language"/>                 <item id="isbn 56-78" name="stock market" price="$8.50" author="bob" catalog="business"/>                 <item id="isbn aa-02" name="guideline health" price="$19.00" author="lee" catalog="health"/>                 <item id="isbn a4-07" name="c# inside" price="$8.50" author="bob" catalog="language"/>             </info>         </x:xdata>     </xmldataprovider>     <collectionviewsource x:key='src' source="{binding source={staticresource mydata}, xpath=item}">         <collectionviewsource.groupdescriptions>             <propertygroupdescription propertyname="@catalog"/>         </collectionviewsource.groupdescriptions>     </collectionviewsource>     <!--data--> </window.resources> <grid>     <dg:datagrid      autogeneratecolumns="false"      background="white" isreadonly="true" padding="0" margin="0"      borderthickness="0"      gridlinesvisibility="none"      horizontalscrollbarvisibility="disabled"         headersvisibility="all"      itemssource='{binding source={staticresource src}}'      selectionmode="single"          selectionunit="fullrow"      verticalgridlinesbrush="darkgray"      verticalscrollbarvisibility="disabled">         <dg:datagrid.columns>             <dg:datagridtextcolumn binding="{binding xpath=@id}" header="id"/>             <dg:datagridtextcolumn binding="{binding xpath=@name}" header="name"/>             <dg:datagridtextcolumn binding="{binding xpath=@price}" header="price"/>             <dg:datagridtextcolumn binding="{binding xpath=@id}" header="author"/>         </dg:datagrid.columns>      </dg:datagrid> </grid> 

xaml:    <dg:datagrid name="sc_dglist"  canuseraddrows="false" loaded="sc_dglist_loaded"> 

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cs:

private void sc_dglist_loaded(object sender, routedeventargs e)  {       sc_dglist.selectedindex = -1;  }