ListBoxItem produces "System.Windows.Data Error: 4" binding error

Question

I have created the fallowing ListBox:

<ListBox x:Name="RecentItemsListBox" Grid.Row="1" BorderThickness="0" Margin="2,0,0,0" SelectionChanged="RecentItemsListBox_SelectionChanged">
  <ListBox.Resources>
      <Style TargetType="{x:Type ListBoxItem}"
             BasedOn="{StaticResource {x:Type ListBoxItem}}">
          <Style.Triggers>
              <!--This trigger is needed, because RelativeSource binding can only succeeds if the current ListBoxItem is already connected to its visual parent-->
              <Trigger Property="IsVisible" Value="True">
                  <Setter Property="HorizontalContentAlignment"
                          Value="{Binding Path=HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
                  <Setter Property="VerticalContentAlignment"
                          Value="{Binding Path=VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
              </Trigger>
          </Style.Triggers>
      </Style>
  </ListBox.Resources>
  <ListBox.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal" Margin="0,2,0,0">
                <TextBlock Text="{Binding Number}" />
                <StackPanel Orientation="Vertical" Margin="7,0,0,0">
                    <TextBlock Text="{Binding File}" />
                    <TextBlock Text="{Binding Dir}" Foreground="DarkGray" />
                </StackPanel>
            </StackPanel>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

This will produce at runtime the fallowing Line in the OutputWindow of VisualStudio:

System.Windows.Data Error: 4 : 
 Cannot find source for binding with reference 'RelativeSource FindAncestor, 
 AncestorType='System.Windows.Controls.ItemsControl', AncestorLevel='1''. 
 BindingExpression:Path=HorizontalContentAlignment; DataItem=null; 
 target element is 'ListBoxItem' (Name='');

Can someone give me a tip, how I can solve this?

Update:

I have added the Properties to the style to try to eliminate the warning/error.

Convent

Do you need that style at all? why can't you set the alignments on the stackpanel/textblock in the datatemplate? – Boaten

Answer 1

The easiest way to solve this is to ensure that your Listbox has a ItemContainerStyle. See the following example:

<ListBox x:Name="RecentItemsListBox" Grid.Row="1" BorderThickness="0" Margin="2,0,0,0" SelectionChanged="RecentItemsListBox_SelectionChanged">
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}">
            <Setter Property="HorizontalContentAlignment" Value="Left"/>
            <Setter Property="VerticalContentAlignment" Value="Center"/>
        </Style>
    </ListBox.ItemContainerStyle>

...

</ListBox>

What happens is that your Items are being created, and by default they look for parent's property which isn't defined. Explicitly defining it will solve this problem.

I had the same issue using a TreeView and changing the bound source for these templates would cause those warnings.

Gradus

Answer 2

The answer over here resolved this issue for me:

ListBox with Grid as ItemsPanelTemplate produces weird binding errors

Defining a top-level style (in my App.xaml) targeting the problem type "fixed" the issue for me. Here's a style that should work for you:

<Style TargetType="{x:Type ListBoxItem}">
     <Setter Property="HorizontalContentAlignment" Value="Left" />
     <Setter Property="VerticalContentAlignment" Value="Top" />
</Style>

In my case, I was creating some TreeViewItems and then binding my TreeView to the created items. The binding error was occurring because the TreeViewItem's binding was being resolved before they were being added to the TreeView. The correct solution was to not create a TreeViewItem, but instead create a class that contained the data I needed (Header and Items). Just relaying my situation in case there are parallels with your own.

Maiga

Answer 3

For me, the culprit was a TreeView, not a ListView. I added the global style to my App.xaml as suggested by @bsegraves:

<Style TargetType="{x:Type TreeViewItem}">
    <Setter Property="HorizontalContentAlignment" Value="Left" />
    <Setter Property="VerticalContentAlignment" Value="Top" />
</Style>

I also had to add the following to my TreeView:

<TreeView.ItemContainerStyle>
    <Style
        BasedOn="{StaticResource {x:Type TreeViewItem}}"
        TargetType="{x:Type TreeViewItem}">         
    </Style>
</TreeView.ItemContainerStyle>

For some reason, the BasedOn attribute was the missing piece. (I tried @Etienne's approach, but it didn't work.)

Unwinking

Answer 4

Another workaround that worked for me was to suppress these errors (actually, it seems more appropriate to call them warnings) by setting the data binding source switch level as critical in constructor of the class or a top level window -

#if DEBUG     
    System.Diagnostics.PresentationTraceSources.DataBindingSource.Switch.Level =
        System.Diagnostics.SourceLevels.Critical;
#endif

Ref.: How to suppress the System.Windows.Data Error warning message

Update: This is not the best solution but for warnings which are harmful this looks good to me.

Graveyard

blogged about this here - weblogs.asp.net/akjoshi/archive/2011/11/30/… – Graveyard

This is a bad idea. First off, the errors only show in Visual Studio, so it's not a user facing error. Secondly, you'll HIDE THE ERROR. The error is there for a reason, and hiding it (along with all of it's brothers and sisters) will most likely make you worse off in the long run. Fix the error, don't hide it! – Chanda

I kind of disagree. We are grown-ups who can remember that we've disabled the error for a while, and revisit the issues when it becomes more important for the needs of our app. You can think of the error as an overzealous warning about what would otherwise be a crude--but useful--sort of WPF covariance: you can bind a ListView row to a less-derived object and it's nice to have those fields that the runtime object doesn't happen to have, be blank. – Spermous

It seems wrong to hide the error generally simply because of one scenario that is spitting it out. – Capeskin

Answer 5

These HorizontalContentAlignment and VerticalContentAlignment issues are caused because the container is not defining its HorizontalAlignment and VerticalAlignment respectively.

So instead of making generic style(s) for ListBoxItem, TreeViewItem or worse exhaustively setting those properties directly, I made a generic style for ItemsControl in my App.xaml that solved whatever is causing this issue like this:

<Style TargetType="{x:Type ItemsControl}">
        <Setter Property="HorizontalAlignment" Value="Left" />
        <Setter Property="VerticalAlignment" Value="Top" />
</Style>

Undercarriage