如何根据属性隐藏wpf datagrid列

Question

I have the following WPF sample program:

Xaml:

<Window x:Class="AncestorArie.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <BooleanToVisibilityConverter x:Key="BoolToVis" />
    </Window.Resources>
    <Grid>
        <DataGrid AutoGenerateColumns="False" Name="Blumen" 
                  ItemsSource="{Binding Leaves}">
            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding Color}" 
                                    Header="Farbe" Width="160" />
                <DataGridTextColumn Binding="{Binding Size}" 
                                    Header="Größe" Width="60"
                                    Visibility="{Binding Path=DataContext.Flag, 
                                                RelativeSource={RelativeSource Findancestor, 
                                                AncestorType={x:Type Window}}, 
                                                Converter={StaticResource BoolToVis}}" />
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

Code behind:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        Flowers rose = new Flowers();
        rose.Leaves = new ObservableCollection<Leaf>();

        rose.Flag = false;

        Leaf L1 = new Leaf();
        L1.Color = "rot";
        L1.Size = 3;
        rose.Leaves.Add(L1);

        Leaf L2 = new Leaf();
        L2.Color = "gelb";
        L2.Size = 2;
        rose.Leaves.Add(L2);

        this.DataContext = rose;            
    }
}

And the model classes are:

public class Leaf
{
    public string Color { get; set; }
    public int Size { get; set; }
}

public class Flowers
{
    public bool Flag { get; set; }
    public ObservableCollection<Leaf> Leaves { get; set; }
}

As you can see, I want to hide the 2nd datagrid column, if the Flag property is set to false. But it doesn't work. I get the following binding error in the Visual Studio Output window:

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Window', AncestorLevel='1''. BindingExpression:Path=DataContext.Flag; DataItem=null; target element is 'DataGridTextColumn' (HashCode=44856655); target property is 'Visibility' (type 'Visibility')

What is wrong in my code concerning the Visibility attribute?

Answer 1

A column in a datagrid is an abstract object which does not appear in the visual tree, thus you cannot use RelativeSource -binding, ElementName will not work either since it will not find a governing FrameworkContentElement so you are in kind of a bind.

One way that works is via Source and x:Reference , for that you will need to name your window and move the column to its resources to avoid a cyclical dependency error:

<Window Name="_window" ...>
    <Window.Resources>
        <DataGridTextColumn x:Key="ThatPeskyColumn"
                            Binding="{Binding Size}"
                            Visibility="{Binding DataContext.Flag, Source={x:Reference _window}, Converter={StaticResource BoolToVis}}"/>
    </Window.Resources>
    <!-- ... -->
        <DataGrid AutoGenerateColumns="False" Name="Blumen" 
                  ItemsSource="{Binding Leaves}">
            <DataGrid.Columns>
                <StaticResource ResourceKey="ThatPeskyColumn"/>
                <!-- ... -->

Great fun.

Answer 2

I would prefer a more elegant approach which involves using a Freezable .

<Window.Resources>

    <DiscreteObjectKeyFrame x:Key="FlagKey" Value="{Binding Flag}"/>

</Window.Resources>


<DataGridTextColumn ... Visibility="{Binding Value, Source={StaticResource FlagKey}, ...}" />

Answer 3

Visibility on DataGridTextColumn is not a DependencyProperty and can't be databound. Use a DataGridTemplateColumn and bind the visibility of the controls within the template.

Edit: Actually, this statement only applies to silverlight. See this other SO question for further details.

How to bind DataGridColumn.Visibility?

I asked about the easiest way to tell whether a property is a dependency here.

How can I most easily determine whether a property is a dependency property?

Answer 4

Solution proposed by HB is really good and has true WPF MVVM spirit. Use it where possible.

In my particular case something went wrong so I came out with different way, as my project is not strict MVVM, so I can use coded solution.

In CustomView.xaml name assigned to column:

<DataGrid>
    <DataGrid.Columns>
        <DataGridTemplateColumn x:Name="MachinesColumn" ... />
        ...

In CustomView.xaml.cs we have a simple property which directly changes visibility of column:

public Visibility MachinesColumnVisible
{
    get { return MachinesColumn.Visibility; }
    set
    {
        if (value == MachinesColumn.Visibility)
            return;
        MachinesColumn.Visibility = value;
    }
}