WPF中ListView的选择问题

绑定数据的网络型ListView，里面的CheckBox如何选定？<Window.Resources>
        <!--Define data for ListView-->
        <XmlDataProvider x:Key="MyFile" XPath="/Files">
            <x:XData>
                <Files xmlns="">
                    <File type="Thumbs.db" message="图片预览缩略图文件"/>
                    <File type="*.temp" message="临时文件"/>
                    <File type="*.tmp" message="临时文件"/>
                </Files>
            </x:XData>
        </XmlDataProvider>        <!--Define the template for the first column to contain a CheckBox control-->
        <DataTemplate x:Key="FirstCell">
            <StackPanel Orientation="Horizontal">
                <CheckBox IsChecked="{Binding Path=IsSelected,RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ListViewItem}}}"/>
            </StackPanel>
        </DataTemplate>
    </Window.Resources>
<ListView Grid.Row="1" Name="mylistview" ItemsSource="{Binding Source={StaticResource MyFile},XPath=File}" SelectionMode="Multiple">            <ListView.View>
                <GridView AllowsColumnReorder="False">
                    <GridViewColumn Width="25" CellTemplate="{StaticResource FirstCell}" />
                    <GridViewColumn Header="类型" Width="123" DisplayMemberBinding="{Binding XPath=@type}"/>
                    <GridViewColumn Header="说明" Width="176" DisplayMemberBinding="{Binding XPath=@message}"/>
                </GridView>
            </ListView.View>
        </ListView>如何通过点击Button实现checkBox的选中状态