C# DataGrid中RowDetailsTemplate内的按钮-如何知道单击了哪一行？

我有这个XAML

<DataGrid.RowDetailsTemplate>
    <DataTemplate>
        <StackPanel>
            <Button Content="Reply" Name="btnReply" Click="btnReply_Click" HorizontalAlignment="Left" Margin="5" Padding="10,0" />
            <Label Content="{Binding Path=Subject}" FontWeight="Bold" />
            <Label Content="{Binding Path=Body}" />
        </StackPanel>
    </DataTemplate>
</DataGrid.RowDetailsTemplate>

绑定到列表的DataGrid 在btnReply_内单击我想获取MyObject的实例

我该怎么做

var myObject = (sender as FrameworkElement).DataContext as MyObject;

因为DataContext是继承的