WPF unwanted grid splitter behaviour

Question

Hello,

I have a simple grid with 3 columns (one of which contains a grid splitter). When resizing the grid and the left column reaches its minimum width, instead of doing nothing it increases the width of the right column. Could anyone help me stop this?

I can't set the max width of the right column, because the grid itself also resizes.

Here's some sample code that shows the problem. While resizing, move the mouse over the red area:

XAML:

<Grid DockPanel.Dock="Top" Height="200">
    <Grid.ColumnDefinitions>
        <ColumnDefinition MinWidth="200" Width="*" />
        <ColumnDefinition Width="3" />
        <ColumnDefinition MinWidth="120" Width="240" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="*" />
    </Grid.RowDefinitions>
    <Rectangle Fill="Red" Grid.Row="0" Grid.Column="0" />
    <DockPanel LastChildFill="True" Grid.Row="0" Grid.Column="2" >
        <Rectangle DockPanel.Dock="Right" Width="20" Fill="Blue" />
        <Rectangle Fill="Green" />
    </DockPanel>
    <GridSplitter Background="LightGray" Grid.Row="0" Grid.Column="1" Height="Auto" Width="Auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" />
</Grid>

Answer 1

I got this undesirable behaviour to stop by changing the * in the columndefinition to Auto and the 240 to *.

Answer 2

This approach is a hack but can be used for the desired effect. Try putting an event handler on the Window.SizeChanged event to set the maxWidth of the first columndef. For example:

private void Window_SizeChanged(object sender, SizeChangedEventArgs e)
{
     int borderBuffer = 9;
     //              AppWindow Size    Splitter Width     Far Column Min  FudgeFactor                
     Col0.MaxWidth = e.NewSize.Width - Col1.Width.Value - Col2.MinWidth - borderBuffer;
}

I needed to use this method to prevent a third party control in the top row of the grid from having some undesirable wrapping resulting from when the gridSplitter disregards the min/max width of the column with width set to "Auto". The borderBuffer may need to be adjusted for your case. The borderBuffer in my case didn't make perfect sense based on the geometry/column/border widths - it was just the magic number that worked for my layout.

If someone can come up with a cleaner solution, I'd love to use it instead. This solution reminds me of painfully trying to force VB6 to resize controls - yuck. But for now, it beats having items on the top row of my grid from getting hidden due to unexpected wrapping.