>Hi,
>This should be simple but it's beating me. Here's a simple XAML window:

<Window x:Class="WpfApplication1.Window23"
>    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
>      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
>      Title="ScrollViewer Test">
>    <StackPanel >
>        <ScrollViewer  HorizontalScrollBarVisibility="Auto">
>            <Rectangle Width="500" Height="500" Fill="Red" />
>        </ScrollViewer>
>    </StackPanel>
></Window>

>When I run this and make the window narrower then the horizontal scrollbar kicks in when required. If, however, I reduce the height of the window then the minimum height of the StackPanel (and ScrollViewer) is constrained by the height of the Rectangle (if I switch the Orientation of the StackPanel I get the opposite behaviour (i.e vertical Scrollbar works) )
>
>I assume the solution to this may be to override Measure/Arrange somewhere - or maybe to wrap the ScrollViewer in something other than a StackPanel - but can't seem to find anything that will work :-{
>
>UPDATE: Ha, DockPanel works. But it would be good to find a solution when using StackPanel.....

Grid also works, and in this case, no parent also works.

From what I've seen, StackPanel's always respect the sizing requests of their child objects in the direction of flow, so they do not make good parents for a dynamically sized ScrollViewer.

Here's my solution:

<Window x:Class="WpfApplication2.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      Title="ScrollViewer Test"
        Name="myWindow">
  <Grid Name="myGrid">
    <StackPanel>
      <ScrollViewer  HorizontalScrollBarVisibility="Auto" Height="{Binding Path=ActualHeight, ElementName=myGrid  }" >
        <Rectangle Width="500" Height="500" Fill="Red" />
      </ScrollViewer>
    </StackPanel>
  </Grid>
</Window>

That's probably is not worth using, but it show one way to work around it. The basic fix is to set the height for the scroll viewer to the desired size. You could also add a converter to the binding if for instance you wanted the scroll viewer to take up 30% of the space of the grid.