WPF 中 DataGridColumn 的绑定可见性

Question

How can I hide a column in a WPF DataGrid through a Binding?

This is what I did:

<DataGridTextColumn Header="Column header"
                    Binding="{Binding ColumnValue}"
                    Width="100"
                    ElementStyle="{StaticResource DataGridRightAlign}"
                    Visibility="{Binding MyColumnVisibility}" />

And this is what I got (besides the column still visible):

System.Windows.Data Error: 2: Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=MyColumnVisibility; DataItem=null; target element is 'DataGridTextColumn' (HashCode=1460142); target property is 'Visibility' (type 'Visibility')

How to fix the binding?

Answer 1

First of all, DataGridTextColumn (or any other supported dataGrid column) does not lie in the Visual tree of the DataGrid . Hence, by default it doesn't inherit the DataContext of the DataGrid . However, it works for Binding DP only and for no other DP's on DataGridColumn.

Since they don't lie in the same VisualTree, any attempt to get the DataContext using RelativeSource won't work as well because DataGridTextColumn is unable to traverse up to the DataGrid .

There are two other ways to achieve this though:

---

First using a Freezable class. Freezable objects can inherit the DataContext even when they're not in the visual or logical tree –We can take advantage of that.

First, create a class inheriting from Freezable and Data DP which we can use to bind in XAML:

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));
}

Now, add an instance of it in DataGrid resources so that it can inherit the DataGrid's DataContext and can bind with its Data DP:

    <DataGrid>
        <DataGrid.Resources>
            <local:BindingProxy x:Key="proxy" Data="{Binding}"/>
        </DataGrid.Resources>
        <DataGrid.Columns>
            <DataGridTextColumn Visibility="{Binding Data.MyColumnVisibility,
                                                Source={StaticResource proxy}}"/>
        </DataGrid.Columns>
    </DataGrid>

---

Second , you can refer to any UI element in XAML using ElementName or x:Reference . However, ElementName works only in the same visual tree, whereas x:Reference doesn't have such constraints.

So, we can use that as well to our advantage. Create a dummy FrameworkElement in XAML with Visibility set to collapsed . The FrameworkElement will inherit the DataContext from its parent container, which can be a Window or UserControl.

And can use that in DataGrid:

    <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>

Answer 2

<Window.Resources>
    <ResourceDictionary>
        <FrameworkElement x:Key="ProxyElement" DataContext="{Binding}" />
    </ResourceDictionary>
</Window.Resources>

<!-- Necessary for binding to resolve: adds reference to ProxyElement to tree.-->
<ContentControl Content="{StaticResource ProxyElement}" Visibility="Collapsed" />
<mch:MCHDataGrid Height="350"
                  AutoGenerateColumns="False"
                  FlowDirection="LeftToRight"
                  ItemsSource="{Binding PayStructures}"
                  SelectedItem="{Binding SelectedItem}">
    <DataGrid.Columns>
         <DataGridTemplateColumn Width="70"
                                 Header="name"
                                 IsReadOnly="True"
                                 Visibility="{Binding DataContext.IsShowName,
                                 Source={StaticResource ProxyElement}}">
             <DataGridTemplateColumn.CellTemplate>
                 <DataTemplate>
                     <TextBlock Text="{Binding FieldName}" />
                 </DataTemplate>
             </DataGridTemplateColumn.CellTemplate>
         </DataGridTemplateColumn>                   
     </DataGrid.Columns>
</mch:MCHDataGrid>

Sample of bound property in view model:

private Visibility _isShowName;

public Visibility IsShowName
{
    get { return _isShowName; }
    set
    {
        _isShowName = value;
        OnPropertyChanged();
    }
}

Answer 3

Another easy solution I like is to add a dummy collapsed FrameworkElement at the same level as the DataGrid . The FrameworkElement can then be used as the Source of the Binding with the x:Reference markup extension.

For example like this:

<FrameworkElement x:Name="FrameWorkElementProxy" Visibility="Collapsed"/>
<DataGrid>
    <DataGrid.Columns>
        <DataGridTemplateColumn Header="post" 
            Visibility="{Binding DataContext.DataGridColumnVisibility, Source={x:Reference Name=FrameWorkElementProxy}}"/>
    </DataGrid.Columns>
</DataGrid>

Answer 4

Another fast option if you have created the Window/Page/UserControl DataContext object in the XAML like this:

<Window.DataContext>  
    <local:ViewModel x:Name="MyDataContext"/>  
</Window.DataContext>

is that you can add x:Reference using the x:Name of the DataContext object in the Source of the binding:

<DataGridTextColumn Header="Column header"
                    Binding="{Binding ColumnValue}"
                    Width="100"
                    ElementStyle="{StaticResource DataGridRightAlign}"
                    Visibility="{Binding MyColumnVisibility, Source={x:Reference Name=MyDataContext}}"

That way you can avoid using Binding DataContext.MyColumnVisibility , and just use Binding MyColumnVisibility