LongListSelector锁定组头（sticky header ）之我的实现

LongListSelector如何实现类似于WP7手机程序列表的效果，将屏幕显示范围内的第一个分组的GroupHeader一直显示在列表的最上方。
国内国外论坛上问的不少，可都没有实现。

无耐之下自己动手搞定，闲话少续，开讲.....

核心思想：取得当前LongListSelector控件可视范围内的第一条数据，取得它的分组名称，然后自己制做一个组头(在我的示例它叫做borderGroupName)，覆盖在LongListSelector控件之上。

[html]
<span style="font-size:12px;"> <Border BorderThickness="0" BorderBrush="White" Visibility="Visible"
                      Background="Black"   Canvas.ZIndex="10"   Width="300"   Height="80"   VerticalAlignment="Top" RenderTransformOrigin="0.5,0.5" Grid.Row="1" Name="borderGroupName"   >
                    <Border.RenderTransform>
                        <CompositeTransform TranslateX="-78"/>
                    </Border.RenderTransform>
                    <StackPanel>
                        <Border Background="Transparent" Margin="12,8,0,8" Width="300" >
                            <Border Background="{StaticResource PhoneAccentBrush}"
                                         Width="62" Height="62"
                                    MouseLeftButtonDown="Border_MouseLeftButtonDown"
                                        HorizontalAlignment="Left">
                                <TextBlock Text="a"
                                               Foreground="#FFFFFF"
                                               FontSize="48"
                                           Margin="8,0,0,0"
                                               FontFamily="{StaticResource PhoneFontFamilySemiLight}"
                                               HorizontalAlignment="Left"
                                               Name="txtGroupName"

                                               VerticalAlignment="Bottom"/>
                            </Border>
                        </Border>
                    </StackPanel>
                </Border>

                <Border BorderThickness="0" BorderBrush="Red"   Canvas.ZIndex="0">
                    <toolkit:LongListSelector x:Name="regionSelector" Background="Transparent"
                                          GroupViewOpened="LongListSelector_GroupViewOpened"
                                          GroupViewClosing="LongListSelector_GroupViewClosing"
                                             .........

补充：移动开发 , Windows Phone ,