WPF DataGrid Visibility的绑定

　　场景：根据配置文件显示DataGrid中的某些列。

　　问题：Columns集合只是DataGrid的一个属性，这个集合在逻辑树或视觉树中是看不到的，也不会继承DataContext属性。

　　通过网上查阅各种资料，方法可以归结以下几种，下面将一一展示。

　　方法一：对DataGridColumn附加DataContext属性

　　该方法需要用到一个帮助类（需要创建一个全局实例），具体内容如下：

public class DataGridContextHelper
    {
        static DataGridContextHelper()
        {

            DependencyProperty dp = FrameworkElement.DataContextProperty.AddOwner(typeof(DataGridColumn));
            FrameworkElement.DataContextProperty.OverrideMetadata(typeof(DataGrid),
            new FrameworkPropertyMetadata
               (null, FrameworkPropertyMetadataOptions.Inherits,
               new PropertyChangedCallback(OnDataContextChanged)));

        }

        public static void OnDataContextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            DataGrid grid = d as DataGrid;
            if (grid != null)
            {
                foreach (DataGridColumn col in grid.Columns)
                {
                    col.SetValue(FrameworkElement.DataContextProperty, e.NewValue);
                }
            }
        }
    } 

　　前台绑定示例

<DataGridTextColumn x:Name="col2" Header="TestColumn"
                                    Visibility="{Binding (FrameworkElement.DataContext).Show,RelativeSource={RelativeSource Self},Converter={StaticResource cc}}"></DataGridTextColumn>

　　后台绑定示例

var binding = new Binding();
            binding.Mode = BindingMode.OneWay;
            binding.RelativeSource=new RelativeSource(RelativeSourceMode.Self);
            binding.Converter = new BooleanToVisibilityConverter();
            binding.Path=new PropertyPath("(FrameworkElement.DataContext).Show");
            BindingOperations.SetBinding(obj, DataGridColumn.VisibilityProperty, binding);

　　方法二：通过Source直接与Vm绑定

　　示例代码：

var binding = new Binding();
            binding.Mode = BindingMode.OneWay;
            binding.Source = vm;
            binding.Converter = new BooleanToVisibilityConverter();
            binding.Path = new PropertyPath("Show");
            BindingOperations.SetBinding(obj, DataGridColumn.VisibilityProperty, binding);

　　方法三：通过Source与VM的一个代理类进行绑定

　　代理类

　　Freezable可以继承DataContext即使它们不在视觉树或逻辑树中

public class BindingProxy : Freezable
    {
        #region Overrides of Freezable

        protected override Freezable CreateInstanceCore()
        {
            return new BindingProxy();
        }

        #endregion

        public object Data
        {
            get { return (object)GetValue(DataProperty); }
            set { SetValue(DataProperty, value); }
        }

        public static readonly DependencyProperty DataProperty =
            DependencyProperty.Register("Data", typeof(object),
                                         typeof(BindingProxy));
    }

　　前台绑定代码

 <DataGrid x:Name="dg" HorizontalAlignment="Left" VerticalAlignment="Top" Height="253" Width="436" ItemsSource="{Binding Persons}"
                  AutoGenerateColumns="False">
            <DataGrid.Resources>
                <dgTest:BindingProxy x:Key="proxy" Data="{Binding}"/>
            </DataGrid.Resources>
            <DataGrid.Columns>
                <DataGridTextColumn x:Name="col1" Header="TestColumn" Binding="{Binding Name}"></DataGridTextColumn>
                <DataGridTextColumn x:Name="col2" Header="TestColumn"
                                    Visibility="{Binding (FrameworkElement.DataContext).Show,RelativeSource={RelativeSource Self},Converter={StaticResource cc}}"></DataGridTextColumn>
                <DataGridTextColumn x:Name="col3" Header="TestColumn"
                                    Visibility="{Binding Data.Show,Source={StaticResource proxy},Converter={StaticResource cc}}"></DataGridTextColumn>
            </DataGrid.Columns>
        </DataGrid>

　　方法四：通过一个代理控件来实现

　　代理控件与代理对象的解决方式类似，都是因为其可以继承DataContext属性，只是一个在逻辑树中看的到，一个看不到。示例如下：

<FrameworkElement x:Name="dummyElement" Visibility="Collapsed"/>
    <DataGrid>
        <DataGrid.Columns>
            <DataGridTextColumn Header="Test"
                                Binding="{Binding Name}"
                                Visibility="{Binding DataContext.IsEnable,
                                          Source={x:Reference dummyElement}}"/>
        </DataGrid.Columns>
    </DataGrid>