DataGrid Column Header binding inside Expander: Binding source not found when expander is collapsed

Question

I have DataGrid which has a column that is to be shown/hidden depending on a property. I have had no luck in showing/hiding the column, so we ended up taking the column out and put it in a separate DataGrid and place the second DataGrid inside an Expander. The header of the second DataGrid is bound the the DataContext of the Expander (or DataGrid - same effect, have also tried binding it to the containing usercontrol).

            <Expander ExpandDirection="Right" Style="{DynamicResource ExpanderDirectionRight}" IsExpanded="{Binding ShowLaterDate}">
                <DataGrid AutoGenerateColumns="False" AlternationCount="2" SelectionMode="Single" ItemsSource="{Binding Rows, UpdateSourceTrigger=PropertyChanged}" CanUserDeleteRows="True" CanUserAddRows="False" CanUserResizeColumns="False" SnapsToDevicePixels="True" Visibility="{Binding Rows.HasContent, Converter={StaticResource BooleanToVisibilityConverter}}" HorizontalAlignment="Left" SelectedIndex="{Binding SelectedIndex, ElementName=BudgetDataGrid}">
                    <DataGrid.Columns>
                        <DataGridTemplateColumn CellTemplate="{StaticResource LaterDataTemplate}" Width="{StaticResource WidthOfValueColumns}">
                            <DataGridTemplateColumn.Header>
                                <Grid Margin="{StaticResource MarginOfTextBox}">
                                    <userControls:DateOrAgeEditor Date="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Expander}}, Path=DataContext.LaterDate, UpdateSourceTrigger=LostFocus}" DateOfBirth="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Expander}}, Path=DataContext.DateOfBirth}" TabIndex="11"/>
                                </Grid>
                            </DataGridTemplateColumn.Header>
                        </DataGridTemplateColumn>
                    </DataGrid.Columns>
                </DataGrid>
            </Expander>

This is all good an well.

Problem: The bound value is shown when the usercontrol is displayed. BUT ONLY if the Expander is expanded! If the Expander is collapsed when the usercontrol is displayed this is printed to output:

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.Expander', AncestorLevel='1''. BindingExpression:Path=DataContext.DateOfBirth; DataItem=null; target element is 'DateOrAgeEditor' (Name='UserControl'); target property is 'DateOfBirth' (type 'DateTime')
System.Windows.Data Warning: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.Expander', AncestorLevel='1''. BindingExpression:Path=DataContext.LaterDate; DataItem=null; target element is 'DateOrAgeEditor' (Name='UserControl'); target property is 'Date' (type 'DateTime')

When the Expander is then expanded the binding is not updated and continues to be 'broken'.

Question: How do I get the binding to bind correctly even when the Expander is not initially expanded?

Answer 1

Just found a way of binding the Visibility of my column (http://www.thomaslevesque.com/2011/03/21/wpf-how-to-bind-to-data-when-the-datacontext-is-not-inherited/) this has however reintroduced the same problem as the expander. But easy to fix, just use the same kind of binding for the header-content as for the visibility.