Cannot find source for binding with reference 'RelativeSource FindAncestor

Question

I am using a compositecollection:

• Comboboxitem with content "Select a vendor"
• Collectioncontainer bound to a Observablecollection of Vendor objects

The desired functionality: the user has to select a vendor from the combobox. Selecting "Select a vendor" sets the Vendor property in the viewmodel to null.

I am getting an binding error. Any ideas how to fix this?

Error when debugging

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

XAML

<ComboBox Name='cmbVendor'
            SelectedItem='{Binding Vendor, Converter={StaticResource ComboboxConverter}, Mode=TwoWay}'
            IsSynchronizedWithCurrentItem='True'>
    <ComboBox.Resources>
      <CollectionViewSource x:Key='VendorsCollection'
                            Source='{Binding Vendors}' />
      <DataTemplate DataType='{x:Type ComboBoxItem}'>
        <TextBlock Text='{Binding Content}' />
      </DataTemplate>
      <DataTemplate DataType='{x:Type objects:Vendor}'>
        <StackPanel>
          <TextBlock Text='{Binding Name}' />
        </StackPanel>
      </DataTemplate>
    </ComboBox.Resources>
    <ComboBox.ItemsSource>
      <CompositeCollection>
        <ComboBoxItem Content='Select a vendor' />
        <CollectionContainer Collection='{Binding Source={StaticResource VendorsCollection}}' />
      </CompositeCollection>
    </ComboBox.ItemsSource>
  </ComboBox>

ComboboxConverter

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {

      var vendor = value as Vendor;
        if (vendor != null)
        {
            return vendor;
        }

        return null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var vendor = value as Vendor;
        if (vendor != null)
        {
            return vendor;
        }

        var comboboxItem = value as ComboBoxItem;
        if (comboboxItem != null)
        {
            return null;
        }
        return null;
    }

Answer 1

These binding errors are harmless and handled internally so you can safely just ignore them, or suppress them. Please refer to the following link for more information.

Resolving harmless binding errors in WPF: https://weblogs.asp.net/akjoshi/resolving-un-harmful-binding-errors-in-wpf