Datagrid有多个bug；
1，不支持DynamicResource的东西
2， 在Column隐藏后再显示， ColumnHeader的Tag或者DataContext为null。

解决办法：
用StaticResource ，如下面的  StaticResource   DGC_ContentTemplate；
用DataGridColumnHeader的Column，来取得上层的datacontext。如，  ItemsSource ="{ Binding   Path =Column.Tag,   Converter   ={ StaticResource   DebugConverter },   Mode =OneWay,   RelativeSource ={ RelativeSource       FindAncestor ,   AncestorType ={ x :   Type   DataGridColumnHeader }}}"

   private void InitDataGridBinding (DataGridColumnEx col, string path)
        {
            if (null == col || String.IsNullOrWhiteSpace (path) || null == col .Header)
            {
                return;
            }

            Binding binding = new Binding();
            binding.Mode = BindingMode. OneWay;
            binding.RelativeSource = new RelativeSource(RelativeSourceMode .Self);
            binding.Converter = new BoolToVisibilityConverter();
            binding.Path = new PropertyPath("(FrameworkElement.DataContext).PACfgVM." + path + ".CfgInfo[" + PAAttachedProperty. GetName(col ) + "].IsVisiable");

            BindingOperations.SetBinding (col, DataGridColumnEx.VisibilityProperty , binding);

            //{for combobox binding in columnHeader
            col.Tag = PAAttachedProperty. GetTag(col );

            DependencyPropertyDescriptor dpd = DependencyPropertyDescriptor .FromProperty( DataGridColumnEx.VisibilityProperty , typeof(DataGridColumnEx ));
            if (dpd != null)
            {
                dpd.AddValueChanged (col, delegate
                {
                    //
                    InitDataGridColumnHeader(col , GetDataGridParent( col));
                });
            }
            //}
        }




             <DataTemplate x :Key="DGC_ContentTemplate">
                <TextBlock TextWrapping ="Wrap" Text="{ Binding }" MinWidth ="20"/>
            DataTemplate>


   < Style x : Key ="DataGridColumnHeaderStyle_ComboBox" TargetType ="{ x : Type DataGridColumnHeader }">
                < Setter Property ="ContentTemplate" Value ="{ StaticResource DGC_ContentTemplate }"/>
                < Setter Property ="VerticalContentAlignment" Value ="Center"/>
                                 < Setter Property ="Template">
                                                 < Setter.Value >
                                                                 < ControlTemplate TargetType ="{ x : Type DataGridColumnHeader }">
                            < Grid >
                                                                                                 < StackPanel Orientation ="Vertical" d : LayoutOverrides ="Height" Margin ="10">
                                    < Label Foreground ="Black" HorizontalContentAlignment ="Left" Content ="{ TemplateBinding Content }"/>
                                   

                                   
                                    < ComboBox Margin ="0,10,0,0"
                                              ItemsSource ="{ Binding Path =Column.Tag, Converter ={ StaticResource DebugConverter }, Mode =OneWay, RelativeSource ={ RelativeSource   FindAncestor , AncestorType ={ x : Type DataGridColumnHeader }}}"> ComboBox >

                                StackPanel >                                                                                                        
                                                                                                 < Thumb x : Name ="PART_LeftHeaderGripper" HorizontalAlignment ="Left" Style ="{ StaticResource ColumnHeaderGripperStyle }"/>
                                                                                                 < Thumb x : Name ="PART_RightHeaderGripper" HorizontalAlignment ="Right" Style ="{ StaticResource ColumnHeaderGripperStyle }"/>
                                                                                 Grid >
                                                                 ControlTemplate >
                                                 Setter.Value >
                                 Setter >

                < EventSetter Event ="Selector.SelectionChanged" Handler ="ComboBox_SelectionChanged"/>
            Style >