wpf gridsplitter issues -- both sides shrink - wpf

Question

Gridsplitter trouble:
I have a: grid with 4 columns
Column 0 contains a grid with 3 columns
Column 1 contains a gridsplitter
Column 2 contains a stackpanel of width 20 pixels
Column 3 contains a grid with 3 columns
When the gridsplitter is moved to either the left or right, BOTH panels shrink the same amount -- one should shrink and the other should grow.
I am hesitant to include the xaml, but you are going to ask for it, so here is an abridged version. I have only removed a few unrelated controls, and gutted the treeviews and listviews. If you really need the whole thing, then of course I can supply it.
Thanks for any help!
<Window x:Class="Calvin.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
Title="Calvin" >
<DockPanel Height="Auto" Width="Auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" LastChildFill="True" >
<Grid DockPanel.Dock="Top" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" RenderTransformOrigin="0.5,0.497" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="1*" />
<ColumnDefinition Width="5" />
<ColumnDefinition Width="20" />
<ColumnDefinition Width="1*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid Grid.Column="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="1*" />
<ColumnDefinition Width="5" />
<ColumnDefinition Width="2*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<TextBox Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="3" TextWrapping="NoWrap" Text="Field One" HorizontalAlignment="Stretch"/>
<TextBox Grid.Row="0" Grid.Column="4" Grid.ColumnSpan="3" TextWrapping="NoWrap" Text="Field Two" HorizontalAlignment="Stretch" />
<TreeView DockPanel.Dock="Left" Grid.Column="0" Grid.Row="1" Name="PaneOneTree"
Width="Auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" >
</TreeView>
<GridSplitter Grid.Column="1" Grid.Row="1" Width="5" HorizontalAlignment="Center"/>
<ScrollViewer Grid.Column="2" Grid.Row="1" >
<ListView DockPanel.Dock="Left" Name="FileDetailsLeft" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="Auto" >
<ListView.View>
<GridView>
<GridViewColumn Header="Name" Width="120" />
<GridViewColumn Header="Size" Width="120" />
<GridViewColumn Header="Access Time" Width="120" />
<GridViewColumn Header="Extension" Width="120" />
</GridView>
</ListView.View>
</ListView>
</ScrollViewer>
</Grid>
<GridSplitter Grid.Column="1" Grid.Row="0" Width="5" HorizontalAlignment="Left" />
<StackPanel Grid.Column="2" Grid.Row="1" VerticalAlignment="Stretch" HorizontalAlignment="Center" Width="Auto" Background="Red">
<Button >Move</Button>
<Button >Other</Button>
</StackPanel>
<Grid Grid.Column="3" Grid.Row="1" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="5" />
<ColumnDefinition Width="auto" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<TextBox Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="3" TextWrapping="NoWrap" Background="Cornsilk"
Text="Pane Two Text" HorizontalAlignment="Stretch"/>
<TextBox Grid.Row="0" Grid.Column="4" Grid.ColumnSpan="3" TextWrapping="NoWrap"
Text="Pane Two Text" HorizontalAlignment="Stretch" Background="Linen" />
<TreeView DockPanel.Dock="Left" Grid.Column="0" Grid.Row="1" Name="PaneTwoTree" Width="Auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"
Background="SeaShell" >
</TreeView>
<GridSplitter Grid.Column="1" Grid.Row="1" Width="5" HorizontalAlignment="Center" />
<ScrollViewer Grid.Column="2" Grid.Row="1" >
<ListView DockPanel.Dock="Left" Name="FileDetailsRight"
HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="Auto" Background="Moccasin" >
<ListView.View>
<GridView>
<GridViewColumn Header="Name" Width="120" />
<GridViewColumn Header="Size" Width="120" />
<GridViewColumn Header="Access Time" Width="120" />
<GridViewColumn Header="Extension" Width="120" />
</GridView>
</ListView.View>
<ListViewItem >List Item</ListViewItem>
<ListViewItem >List Item</ListViewItem>
<ListViewItem >List Item</ListViewItem>
<ListViewItem >List Item</ListViewItem>
<ListViewItem >List Item</ListViewItem>
<ListViewItem >List Item</ListViewItem>
<ListViewItem >List Item</ListViewItem>
</ListView>
</ScrollViewer>
</Grid>
</Grid>
</DockPanel>
</Window>
And, of course, feel free to suggest better ways to do anything:) -- I'm still learning.
:bp:

Answer 1

I had the same issue. When I moved one GridSplitter it would also move the other (Usually in the opposite direction.). I eventually discovered that I had forgotten to set a property of the GridSplitter. For a GridSplitter you MUST have both vertical and horizontal properties set ie...
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<GridSplitter Grid.Column="1" Width="2"
VerticalAlignment="Stretch" HorizontalAlignment="Center"/>
</Grid>

Answer 2

Ok, I see your problem now... basically, you can't set an exact Width on a column who's Width will be changed by a GridSplitter control. Instead, you can only set MinWidth and/or MaxWidth property on the ColumnDefinition, but be aware that you can then not use the "*" notation. Also, looking at the code example below, you can see that you could have stripped out a whole load more code for your question example... this was all that was required to demonstrate your problem (before I fixed it):
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" MinWidth="150" />
<ColumnDefinition Width="5" />
<ColumnDefinition Width="20" />
<ColumnDefinition Width="*" MinWidth="150" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Rectangle Grid.Column="0" Fill="PowderBlue" />
<GridSplitter Grid.Column="1" Background="Black" HorizontalAlignment="Stretch" />
<Rectangle Grid.Column="2" Fill="Red" Height="100" />
<Rectangle Grid.Column="3" Fill="Purple" />
</Grid>