Question

I’m currently working on enabling drag-and-drop support for our company app.
The error I keep getting seems weird to me.
What this says is that

The property 'DragDropHelper.IsDragSource' does not exist in XML namespace 'clr-namespace:DragAndDrop;assembly=DragAndDrop'. Line 61 Position 83

The property is an attached property in the class I found in the Internet in the samples and modified it a bit. Here is property declaration:

namespace DragAndDrop {
public class DragDropHelper
{
    public static readonly DependencyProperty IsDragSourceProperty =    
        DependencyProperty.RegisterAttached("IsDragSource", typeof (bool), typeof (DragDropHelper),
                                            new UIPropertyMetadata(false, IsDragSourceChanged));

    public static bool GetIsDragSource(DependencyObject obj)
    {
        return (bool) obj.GetValue(IsDragSourceProperty);
    }

    public static void SetIsDragSource(DependencyObject obj, bool value)
    {
        obj.SetValue(IsDragSourceProperty, value);
    }

It seems to me that attached property is completely valid, isn’t it?
This DragDropHelper is included into a class library, that I reference from the main client app.
When I try to set the value of the property in a client app:

 <ListView x:Uid="list" x:Name="CurrentFolderItemsControl" drag:DragDropHelper.IsDragSource="true" />

VS2010 says that property doesn’t exist in XML namespace. The XAML document is a resource dictionary
which is merged into main client app resources, because it contains styles for our control.
It’s even more weird because I created a class within main app that has attached property, then set property value in XAML markup – app compiled OK

Answer 1

Problem solved. My error was I didn’t recompile the library after having added attached property. After I did so, everything works as expected. Sorry everybody 🙁