Setting an initial width for an expander or listbox

In a previous question I had asked, I wanted to be able to move the gridsplitter to expand the expander which contains a list box of images so that when it expands, the images resize based on the amout of space available. With help i was able to get the resizing feature to work but the problem now is that when the program initially starts up, the images are full sized instead of thumbnail size. Is there a way to set an initial width of the expander so the images initially show up as thumbnails of about 175 pixels?

ColumnDefinitions:

<Grid.ColumnDefinitions>
    <ColumnDefinition MinWidth="25" Width="*" />
    <ColumnDefinition MinWidth="5" Width="5" />
    <ColumnDefinition Width="2*" />
    <ColumnDefinition MinWidth="5" Width="5" />
    <ColumnDefinition MinWidth="25" Width="*" />
</Grid.ColumnDefinitions>

0: Expander

1: gridsplitter

2: Text box

3: gridsplitter

4: Expander (Text box with images.)

XAML:

<GridSplitter 
    Name="gridSplitter2"
    Width="10" 
    Margin="0,0,0,0" 
    Grid.Column="3"
    IsEnabled="True" 
    HorizontalAlignment="Center"/>
    <Expander
        Style="{DynamicResource ExpanderStyle}"
        Name="pictureExpander"
        IsExpanded="True"
        Grid.Column="4"
        ExpandDirection="Left"
        Collapsed="pictureExpander_Collapsed"
        Expanded="pictureExpander_Expanded" >
        <ListBox 
            Name="photoList" 
            ItemsSource="{Binding Source={StaticResource PhotoBin}}"
            IsSynchronizedWithCurrentItem="True"
            ScrollViewer.CanContentScroll="False"
            ScrollViewer.HorizontalScrollBarVisibility="Disabled">
            <ListBox.ItemContainerStyle>
                <Style TargetType="{x:Type ListBoxItem}">
                    <Style.Resources>
            开发者_如何转开发            <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Yellow" />
                    </Style.Resources>
                    <Style.Triggers>
                        <Trigger Property="IsSelected" Value="True">
                            <Setter Property="BorderBrush" Value="Black"/>
                            <Setter Property="BorderThickness" Value="5"/>
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </ListBox.ItemContainerStyle>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Image 
                        Name="thumbnailImage"
                        Source="{Binding FileLocation}"
                        Margin="5"
                        Stretch="UniformToFill"
                        StretchDirection="Both"
                        HorizontalAlignment="Stretch"
                        />
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Expander>

I think you can play around with your ColumnDefinitions. Setting a Width on your fifth ColumnDefinition will give you a starting Width for it

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition Width="175"/>
    </Grid.ColumnDefinitions>
    <!-- Your other Controls.. -->
    <GridSplitter Grid.Column="3" ... />
    <Expander Grid.Column="4" ... />
</Grid>

Update

I'm unable to reproduce your problem. When I set Width="175" on the fifth ColumnDefinition it starts up with this width. Uploaded my sample app here: http://www.mediafire.com/?kjc9yqgmkq6dbiq