Question

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" />
        <ColumnDefinition Width="auto"/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <!-- … -->
    </Grid.RowDefinitions>
    <TextBlock Grid.Column="0">
        This should be allways visible, even if the expander isn’t expanded!
    </TextBlock>
    <Expander ExpandDirection="Left" Grid.Column="1">
        <Expander.Header>
            <!-- … -->
        </Expander.Header>
        <TreeView MinWidth="50"/>
    </Expander>
    <!-- … -->
</Grid>

I want the user to be able to resize the TreeView. I tried to warp the TreeView in a Grid with 2 columns and a GridSplitter in the first column, but that didn’t work. Does anybody have an idea how to make that work?

P.S.: A XAML-only answer would be great.

Answer 1

You may solve your problem using Expander.Collapsed and Expander.Expanded events as Attached Event. I do not have the idea about only using Xaml now, but the following code works well in my case.

Xaml

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow">
    <Grid Expander.Collapsed="Grid_Collapsed" Expander.Expanded="Grid_Expanded">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="auto"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <!-- … -->
        </Grid.RowDefinitions>
        <TextBlock Grid.Column="0" TextWrapping="Wrap">
        This should be allways visible, even if the expander isn’t expanded!
        </TextBlock>
        <GridSplitter HorizontalAlignment="Right" VerticalAlignment="Stretch" Width="2" />
        <Expander Background="Yellow" ExpandDirection="Left" Grid.Column="1">
            <Expander.Header>test</Expander.Header>
            <TreeView MinWidth="50"/>
        </Expander>
        <!-- … -->
    </Grid>
</Window>

Codebehinde

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private GridLength _rememberWidth = GridLength.Auto;

    private void Grid_Collapsed(object sender, RoutedEventArgs e)
    {
        var grid = sender as Grid;
        if(grid != null)
        {
            _rememberWidth = grid.ColumnDefinitions[1].Width;
            grid.ColumnDefinitions[1].Width = GridLength.Auto;
        }
    }

    private void Grid_Expanded(object sender, RoutedEventArgs e)
    {
        var grid = sender as Grid;
        if (grid != null)
        {
            grid.ColumnDefinitions[1].Width = _rememberWidth;
        }
    }
}