Whats wrong with my Attached Property for RichTextBox "AttachFlowDocument"

Question

Hi I try to create an Attached Property so that i'm able to bind my FlowDocument to an RichTextBox

Here my Code

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;

namespace Speiseplandienst.Tools
{
    public static class RichTextBoxHelper
    {
        public static FlowDocument GetDocument(DependencyObject obj)
        {
            return (FlowDocument)obj.GetValue(AttachFlowDocumentProperty);
        }

        public static void SetDocument(DependencyObject obj, FlowDocument value)
        {
            obj.SetValue(AttachFlowDocumentProperty, value);
        }

        public static readonly DependencyProperty AttachFlowDocumentProperty =
            DependencyProperty.RegisterAttached(
                "AttachFlowDocument",
                typeof(FlowDocument),
                typeof(RichTextBoxHelper),
                new FrameworkPropertyMetadata(
                    default(FlowDocument),
                    FrameworkPropertyMetadataOptions.AffectsRender | FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
                    OnPropertyChangedCallBack));

        private static void OnPropertyChangedCallBack(
            DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            var richTextBox = (RichTextBox)obj;

            // Parse the XAML to a document (or use XamlReader.Parse())

            try
            {
                // Set the document
                richTextBox.Document = GetDocument(richTextBox);
            }
            catch (Exception)
            {
                richTextBox.Document = new FlowDocument();
            }

            // When the document changes update the source
            richTextBox.TextChanged += (obj2, e2) =>
                {
                    RichTextBox richTextBox2 = obj2 as RichTextBox;
                    if (richTextBox2 != null)
                    {
                        SetDocument(obj, richTextBox2.Document);
                    }
                };
        }
    }
}

here the Stacktrace:

   bei System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
   bei System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri)
   bei System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream)
   bei System.Windows.Application.LoadComponent(Object component, Uri resourceLocator)
   bei Speiseplandienst.Views.MenuItemV.InitializeComponent() in c:\Users\MReimann\Desktop\...\...\...\...\MenuItemV.xaml:Zeile 1.
   bei Speiseplandienst.Views.MenuItemV..ctor() in c:\Users\MReimann\Desktop\...\...\...\...\MenuItemV.xaml.cs:Zeile 24.

and here the Error:

{"\"Binding\" kann nicht für die Eigenschaft \"SetDocument\" vom Typ \"RichTextBox\" festgelegt werden. \"Binding\" kann nur für eine \"DependencyProperty\" eines \"DependencyObject\" festgelegt werden."}

i know what this error means but i don't know how to solve this because don't know what DependencyObject i need ...

it would be nice if somebody could point out which object he expect

Answer 1

The names of the static getter and setter methods for an attached property X have to be GetX and SetX. So if you have an attached property AttachFlowDocument they have to look like this:

public static FlowDocument GetAttachFlowDocument(DependencyObject obj)
{
    return (FlowDocument)obj.GetValue(AttachFlowDocumentProperty);
}

public static void SetAttachFlowDocumentDocument(
    DependencyObject obj, FlowDocument value)
{
    obj.SetValue(AttachFlowDocumentProperty, value);
}