经过进一步的测试与标记扩展，这个问题通过了我的方式一遍又一遍，经过一些更多的谷歌搜索，我想我已经找到一个确认，这是Visual Studio设计器中的一个错误。所有有兴趣的人都应该看看

http://www.hardcodet.net/2008/04/nested-markup-extension-bug

***问候，
René

Currently I'm playing around with WPF data binding and I came to an issue I dont understand. So I post the problem here, maybe you have and idea whats geoing wrong.

At first: I'm working with Visual Studio 2008 under Windows Vista 32bit, the problem is also present in Windows 7 RC1 64bit, latest updates/service packs are installed except Vista, its still running with SP1.

Here is the problem: I'm not able to set a ValueConverter in an inherited Binding class.

Here is my custom binding class:

public class MyBinding : Binding
{
    public MyBinding() : base() { }
    public MyBinding(string path) : base(path) { }
}

This class should do exactly the same as the original Binding class because currently it does not implement any own logic. I can use this class in XAML as follows:

<TextBlock Text="{local:MyBinding SomeProperty}" />

local is the namespace where the MyBinding class is implemented.

Now here comes the first thing I dont understand. VS2008 shows the following error message in its error window (the original message is in german, because I'm running a german system - i dont have the english error message, so I will try to translate)

Kein Konstruktor des MyBinding-Typs weist 1-Parameter auf.

(No constructor of type MyBinding takes 1 argument)

Althoug this error is display the project compiles just fine and the MyBinding class is working as expected. Why Visual Studio does not find the corresponding constructor (wich, I would say, is properly implemented)?

I can prevent these message if I change the XAML code to this:

<TextBlock Text="{local:MyBinding Path=SomeProperty}" />

The error message is gone because the MyBinding's default constructor is called, everything works fine, ok...

Now I would like to set a ValueConverter to my property binding, XAML looks like this:

<Window.Resources>
    <local:MyValueConverter x:Key="converter" />
</Window.Resources>
[...]
<TextBlock Text="{local:MyBinding Path=SomeProperty, Converter={StaticResource converter}}" />
[...]

..., and here I get the following error while compiling (original in german and I think, I've also found the original message in english):

Beim Analysieren einer Markup Extension wurde für den Typ "MS.Internal.Markup.MarkupExtensionParser+UnknownMarkupExtension" die unbekannte Eigenschaft "Converter" gefunden. Zeile X Position Y.

(Unknown property 'Converter' for type 'MS.Internal.Markup.MarkupExtensionParser+UnknownMarkupExtension' encountered while parsing a Markup Extension. Line x position Y)

Now I cannot compile anymore because VS does not find the converter property (wich is a public property of the original Binding class).

I've managed to get the MyBinding class to run with a converter I specify, but only with a little hack: I've added the following property to the MyBinding class:

    public Type ConverterType
    {
        get { return Converter == null ? null : Converter.GetType(); }
        set { Converter = value == null ? null : (IValueConverter)Activator.CreateInstance(value); }
    }

... and XAML changes to this:

<TextBlock Text="{local:MyBinding Path=SomeString, ConverterType=local:MyValueConverter}" />

Now my project compiles and runs fine. Actually I think, its a nice solution, because you dont have to specify the converter as a static resource and the binding expression looks a little bit more clearly to me. But at the end, this cannot be the solution.

So can anyone tell me what I've done wrong? Why I cannot set the Converter property in my custom Binding class?

Thank you! Best regards, René

after some further testing with markup extensions, this issue passed my way over and over again and after some more googling, I think I've found a confirmation, that this is a bug in Visual Studio designer. Everyone, whos interested in that should take a look at

http://www.hardcodet.net/2008/04/nested-markup-extension-bug

Best regards, René