Question

I have a treeView and a stackpanel with message that “There is no items”. So, I want to hide panel if treeView’s items is not empty.

Here is my XAML example:

<TreeView Name="treeDocs" Grid.ColumnSpan="2"/>
<StackPanel Orientation="Horizontal" VerticalAlignment="Top" HorizontalAlignment="Center" 
Margin="51,20,51,0" Name="stkNoDocs"
Visibility="{Binding ElementName=treeDocs, Path=Items,
Converter={StaticResource ResourceKey=ItemsToVisibilityConverter}}">

And here is my Converter’s Convert method:

public object Convert(object value, Type targetType, object parameter,
System.Globalization.CultureInfo culture)
{
    return ((ItemCollection)value).Count == 0 ? Visibility.Visible : Visibility.Collapsed;
}

I’ve used the Style property like this:

<StackPanel.Style>
     <Style TargetType="StackPanel">
          <Setter Property="Visibility" Value="Visible"/>   
          <Style.Triggers>
              <DataTrigger Binding="{Binding ElementName=treeDocs, Path=Items.Count}" Value="0">
                   <Setter Property="Visibility" Value="Hidden"/>
              </DataTrigger>
          </Style.Triggers>
     </Style>
</StackPanel.Style>

• but still same result.

And in design mode everything works perfect! But in fact panel always visible… What’s the problem?

Thank you!

Answer 1

The instance stored in Items never changes (its collection contents do though), hence the binding does not get updated, bind to Items.Count and change the converter accordingly or use a Style with a DataTrigger which would be more appropriate than a converter.

Something like this:

<StackPanel.Style>
    <Style TargetType="{x:Type StackPanel}">
        <Setter Property="Visibility" Value="Collapsed"/>
        <Style.Triggers>
            <DataTrigger Binding="{Binding Items.Count, ElementName=treeDocs}"
                         Value="0">
                <Setter Property="Visibility" Value="Visible"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</StackPanel.Style>

(Default visibility needs to be set in a setter because of dependency property precedence)