Binding the values of the subitems of a collection

Question

Look at this example:

I've created a custom control with a collection as a dependency property and filled the items of the collection with subitems getting the values from a binding. If I create the subitems with fixed values everything works, if I bind their values I get binding errors.

This is the user control with the readonly dependency property:

public partial class UserControl1 : UserControl
{
    private static DependencyPropertyKey TextsPropertyKey = DependencyProperty.RegisterReadOnly("Texts", typeof(ItemCollection), typeof(UserControl1), new FrameworkPropertyMetadata(new ItemCollection()));
    public static DependencyProperty TextsProperty = TextsPropertyKey.DependencyProperty;

    public ItemCollection Texts
    {
        get
        {
            return (ItemCollection)GetValue(TextsProperty);
        }
        set
        {
            SetValue(TextsProperty, value);
        }
    }

    public UserControl1()
    {
        ItemCollection texts = new ItemCollection();
        SetValue(TextsPropertyKey, texts);
        InitializeComponent();
    }
}

This is the Window XAML:

<Window x:Class="ControlList.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:ControlList="clr-namespace:ControlList"
Title="Window1" Height="300" Width="300">
<Grid>
    <ControlList:UserControl1>
        <ControlList:UserControl1.Texts>
            <ControlList:ItemOfTheList Text="{Binding Text1}"></ControlList:ItemOfTheList>
            <ControlList:ItemOfTheList Text="{Binding Text2}"></ControlList:ItemOfTheList>
        </ControlList:UserControl1.Texts>
    </ControlList:UserControl1>
</Grid>
</Window>

The ItemOfTheList class is just an object with a string Dependency property:

public class ItemOfTheList : DependencyObject
{
    public static DependencyProperty TextProperty = DependencyProperty.Register("Text", typeof(string), typeof(ItemOfTheList));

    public string Text
    {
        get
        {
            return (string)GetValue(TextProperty);
        }
        set
        {
            SetValue(TextProperty, value);
        }
    }

    public override string ToString()
    {
        return this.Text;
    }
}

And the item collection is just a non generic FreezableCollection:

public class ItemCollection : FreezableCollection<ItemOfTheList>
{
}

In this way I get the following errors:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Text1; DataItem=null; target element is 'ItemOfTheList' (HashCode=52697953); target property is 'Text' (type 'String') System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Text2; DataItem=null; target element is 'ItemOfTheList' (HashCode=22597652); target property is 'Text' (type 'String')

If I change ItemOfTheList to a FrameworkElement I always get at the output window that the DataContext is null. How can I inherit the datacontext of the UserControl in the ItemOfTheList objects?

Kent Boogaart Kent Boogaart · Accepted Answer · 2011-10-20T19:38:26

Your child items are not part of the logical tree so cannot participate in bindings. Please see my blog post here for details on how to rectify this.

Binding the values of the subitems of a collection

1 Answers