Hulda Hulda - 26 days ago 14
C# Question

How to hide wpf datagrid columns depending on a property

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

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.

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