User control inside ScrollViewer doesn't scroll in WPF - wpf

Question

I have the following code (abbreviated) in my main window:
Although I set both scroll bar visibilities and CanContentScroll properties it doesn't scroll. I assume it has to do with my user control.
<Window>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<TabControl Grid.Column="0" Grid.Row="0" HorizontalAlignment="Stretch" Margin="0" VerticalAlignment="Stretch" Height="Auto" Width="Auto">
<TabItem Header="TEST">
<ScrollViewer HorizontalScrollBarVisibility="Visible" VerticalScrollBarVisibility="Visible" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch">
<my:MY_USER_CONTROL x:Name="myUserControl" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" ScrollViewer.CanContentScroll="True" />
</ScrollViewer>
</TabItem>
</TabControl>
<Button Grid.Column="0" Grid.Row="2" >a button</Button>
<WrapPanel Grid.Column="0" Grid.Row="3" >
</WrapPanel>
</Grid>
</Window>
Abbreviated structure of my user control:
<UserControl>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="183*" />
<ColumnDefinition Width="117*" />
</Grid.ColumnDefinitions>
<TreeView ItemsSource="{Binding Children}" Grid.ColumnSpan="2">
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
<Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
<Setter Property="FontWeight" Value="Normal" />
<Style.Triggers>
<Trigger Property="IsSelected" Value="True">
<Setter Property="FontWeight" Value="Bold" />
</Trigger>
</Style.Triggers>
</Style>
</TreeView.ItemContainerStyle>
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Children}" >
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition></ColumnDefinition>
<ColumnDefinition></ColumnDefinition>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition></RowDefinition>
</Grid.RowDefinitions>
<Grid.Children>
<TextBlock Background="LightGray" Padding="2" Margin="2" Grid.Row="0" Grid.Column="0" Text="{Binding Name}" />
<TextBlock Padding="2" Margin="2" Grid.Row="0" Grid.Column="1" Text="{Binding Content}" />
</Grid.Children>
</Grid>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>
</Grid>
</UserControl>

Answer 1

You need to set it like this. I changed the RowDefinition for Row0 to Height="*" So it will use as much space it can. Then changed place between the ScrollViewer and the TabControl. So the TabControl is a content of the ScrollViewer.
<Window>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<ScrollViewer HorizontalScrollBarVisibility="Auto"
VerticalScrollBarVisibility="Auto"
Grid.Column="0" Grid.Row="0">
<TabControl HorizontalAlignment="Stretch" Margin="0" VerticalAlignment="Stretch"
Height="Auto" Width="Auto">
<TabItem Header="TEST">
<my:MY_USER_CONTROL x:Name="myUserControl"
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
ScrollViewer.CanContentScroll="True" />
</TabItem>
</TabControl>
</ScrollViewer>
<Button Grid.Column="0" Grid.Row="2" >a button</Button>
<WrapPanel Grid.Column="0" Grid.Row="3" >
</WrapPanel>
</Grid>

Answer 2

When you set CanContentScroll to True, the ScrollViewer assumes that your content implements IScrollInfo (which i guess doesn´t).
Try setting CanContentScroll on the ScrollViewer to false, this allows the content to use as much space as it wants and the ScrollViewer takes care of scrolling.
However, depending on the size, number of visuals etc. of your control, this might become a performance issue (e.g. no UI Virtualization when CanContentScroll is set to False).

Answer 3

Looks like the content inside your scrollviewer is the same size as the viewer so there is nothing to scroll?
if you do something like
<ScrollViewer HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch">
<Grid Background="Red">
</Grid>
</ScrollViewer>
Then the grid is the same size as the scroll viewer and will never allow scrolling, if you set the height of the grid to more than the viewer can display you'll get a scroller.
<ScrollViewer HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch">
<Grid Background="Red" Height="500">
</Grid>
</ScrollViewer>