[WPF] RelativeSource FindAncestor issue

Question

Here is the code:

                <GridViewColumn
                                DisplayMemberBinding="{Binding Path=BookId}"
                                Width="100">
                    <GridViewColumn.Header>
                        <Border BorderBrush="Black">
                            <TextBlock Width="{Binding RelativeSource=
                                                            {RelativeSource FindAncestor, 
                                                            AncestorType={x:Type GridViewColumn}}, 
                                                            Path=Width}" Text="ID">
                                <TextBlock.ContextMenu>
                                    <ContextMenu>item1</ContextMenu>
                                </TextBlock.ContextMenu>
                            </TextBlock>
                            </Border>
                    </GridViewColumn.Header>
                </GridViewColumn>

Basically what i am trying to do is to make the TextBlock in the header follow the width of the whole column.

It is not working: the textblock's width always matches the text inside. Any ideas?... Thanks in advance!

Answer 1

There are two problems in your code

1. the GridViewColumn is NOT a visual ancestor of the TextBox, its ancestor is a GridViewColumnHeader
2. You should bind to the ActualWidth of the GridViewColumnHeader, not the Width (if Width is not specified, it will be an invalid number)

So your code becomes :

              <GridViewColumn
                            DisplayMemberBinding="{Binding Path=BookId}"
                            Width="100">
                <GridViewColumn.Header>
                    <Border BorderBrush="Black" >
                        <TextBlock Text="ID" Width="{Binding RelativeSource=
                                                        {RelativeSource FindAncestor, 
                                                        AncestorType={x:Type GridViewColumnHeader}}, 
                                                        Path=ActualWidth}">
                            <TextBlock.ContextMenu>
                                <ContextMenu>item1</ContextMenu>
                            </TextBlock.ContextMenu>
                        </TextBlock>
                        </Border>
                </GridViewColumn.Header>
            </GridViewColumn>