WPF Binding in custom control with nested dependency properties.

Question

Hi,
I have created a custom control that should work similar to a data grid (with columns containing certain properties).
The main class that contains the columns collection object is of type UserControl. The columns collection object contains a collection of column models, which also contains some other properties and nestem models. All of those objects are of type DependecyObject.
Here are some examples of my structure:

 public partial class GridControl : UserControl
    {
        public ColumnsCollection ColumnsCollection
        {
            get { return (ColumnsCollection)GetValue(ColumnsCollectionProperty); }
            set { SetValue(ColumnsCollectionProperty, value); }
        }

        public static readonly DependencyProperty ColumnsCollectionProperty =
            DependencyProperty.Register(
                name: nameof(ColumnsCollection),
                propertyType: typeof(ColumnsCollection),
                ownerType: typeof(GridControl));

{......}

public class ColumnsCollection : DependencyObject
    {
        #region Properties
        public ObservableCollection<Column> ColumnItems
        {
            get { return (ObservableCollection<Column>)GetValue(ColumnItemsProperty); }
            set { SetValue(ColumnItemsProperty, value); }
        }

        public static readonly DependencyProperty ColumnItemsProperty =
            DependencyProperty.Register(
                name: nameof(ColumnItems),
                propertyType: typeof(ObservableCollection<Column>),
                ownerType: typeof(ColumnsCollection),
                typeMetadata: new PropertyMetadata(default));

{...}


public class Column : DependencyObject
    {
        public string Header
        {
            get { return (string)GetValue(HeaderProperty); }
            set { SetValue(HeaderProperty, value); }
        }

        public static readonly DependencyProperty HeaderProperty =
            DependencyProperty.Register(
                name: nameof(Header),
                propertyType: typeof(string),
                ownerType: typeof(Column),
                typeMetadata: new PropertyMetadata(default));

{....}

The definition in xaml looks like this:

 <gridControl:GridControl>
            <gridControl:GridControl.ColumnsCollection>
                <gridControl:ColumnsCollection>
                    <gridControl:ColumnsCollection.ColumnItems>
                        <gridControl:Column Header="{Binding DataContext.SomeProperty}" />
                    </gridControl:ColumnsCollection.ColumnItems>
                </gridControl:ColumnsCollection>
            </gridControl:GridControl.ColumnsCollection>
  </gridControl:GridControl>

I have a problem with binding to a property stored in my DataContext of the view (any other binding to StaticResources works fine), in which my custom control is used. I have tried all approaches - using ElementName that points to my parent UserControl, the RelativeSource with FindAncestor by type approach, nothing has worked for me, the DataContext is null in every case. I receive binding errors like this one:
Cannot find governing FrameworkElement or FrameworkContentElement for target element.

I believe the problem is more about how the dependency objects were defined, maybe I am using the wrong base class or I am missing any additional operation to make it work?

Thanks in advance for any suggestions,
Kind Regards,
Dawid