sort of special accordion like control - wpf

Question

I have put an example link in here:
http://activeden.net/item/xml-horizontal-vertical-accordion-banner-rotator/full_screen_preview/127714?ref=premiumtemplates
I try to achieve something similar (but far more basic) with WPF.
Not the flying text stuff, only the basic navigation idea.
I tried to build it with some expander controls and a stackpanel.
What I came up with is this:
<ItemsControl Grid.Row="1" IsTabStop="False" ItemsSource="{Binding Path=tabs,Mode=OneWay}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<ContentPresenter Content="{Binding}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Orientation="Vertical" />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
I use MVVM, so there is also a template which is applied:
<DataTemplate DataType="{x:Type vm:TabulatorViewModel}">
<Expander HorizontalAlignment="Stretch" VerticalAlignment="Stretch" ExpandDirection="{Binding .direction,Mode=OneWay}" IsExpanded="{Binding .isExpanded,Mode=TwoWay}" Header="{Binding .header,Mode=OneWay}" >
<Expander.Style>
<Style TargetType="{x:Type Control}">
<Setter Property="Template" Value="{StaticResource HorizontalExpanderRight}" />
<Style.Triggers>
<DataTrigger Binding="{Binding .direction}" Value="Left">
<Setter Property="Template" Value="{StaticResource HorizontalExpanderLeft}" />
</DataTrigger>
</Style.Triggers>
</Style>
</Expander.Style>
<StackPanel>
<Label Content="{Binding .seitenInhalt.Header,Mode=OneWay}"></Label>
<TextBox Text="{Binding .seitenInhalt.Inhalt,Mode=OneWay}"></TextBox>
<Button Content="zurück" Command="{Binding .seitenInhalt.MovePreviousCommand}" />
<Button Content="vor" Command="{Binding .seitenInhalt.MoveNextCommand}"/>
</StackPanel>
</Expander>
</DataTemplate>
So, this is working, at least kind of.
two screenshots from my current project to explain the issues:
Could not post picture because of reputation points.
All Items together should use the complete width of the stackpanel, not like in the picture. Could not post picture because of reputation points.
All items should use the complete width, but the one expanded item should have a bigger width then the rest. As on the picture, but the collapsed items should use the remaining space, each by the same amount filling the gap)
Any help would be great, I hope it is possible to understand my goal / issues.

Answer 1

I think what you want to use is a UniformGridPanel or WrapPanel, which will use the full width available, rather than a StackPanel which is made to use the minimum width possible. The panel overview is here.

Answer 2

You'll probably want to use a Grid with the Height/Width of the Columns/Rows set to * if the item is Expanded, or Auto if not.
Also, if you're using a Grid in an ItemsControl, you need to set the Grid.Row/Grid.Column, and Width/Height properties on the ContentPresenter, not the ItemTemplate since the ItemTemplate in a ItemsControl is always wrapped in a ContentPresenter.