静态资源转换器上的属性未绑定

Question

I have a value converter with a property I would like to bind to, but the binding never happens, ie the dependency property in my value converter always is null .
Background: I want to bind an enum to a combo box but have control over the text that is being displayed.

I implemented the value converter like this:

public class EnumDisplayer : DependencyObject, IValueConverter
{
    public static readonly DependencyProperty LocalizerProperty =
        DependencyProperty.Register(
            "Localizer", typeof(ILocalizer), typeof(EnumDisplayer),
            new PropertyMetadata(default(ILocalizer), OnLocalizerChanged));

    public ILocalizer Localizer
    {
        get { return (ILocalizer) GetValue(LocalizerProperty); }
        set { SetValue(LocalizerProperty, value); }
    }

    private static void OnLocalizerChanged(DependencyObject d, 
                                           DependencyPropertyChangedEventArgs e)
    {
        // ...
    }

    //...
}

And I bind it like this:

<UserControl.Resources>
    <Common:EnumDisplayer x:Key="companyTypes"
                          Localizer="{Binding CompanyTypeEnumLocalizer}" />
    <!-- ... -->
</UserControl.Resources>

My class is an adapted version of the EnumDisplayer .

I fail to understand, why OnLocalizerChanged is never called. Can anyone provide some insight?

Answer 1

(Stack Team correct me if I am wrong)... ValueConverters do not automatically support in binding and there are reasons...

1. They arent really something that the WPF framework is actively aware of, given that they dont lie on visual or logical tree.

2. They are used as part of inner markup extensions. This is a merky area. Unless they implement marrkup extensions on their own, they would be bound to.

Although there are ways..

1. Straightforward way is to use MultiBinding instead of single binding. The second binding will replace your converter's need to host a dependncy property.

2. http://www.codeproject.com/KB/WPF/AttachingVirtualBranches.aspx

I hope this helps.

Answer 2

I think this may be because the ResourceDictionary in which you are creating the instance is not part of the visual tree, so it cannot find the DataContext and the Binding therefore always returns null.

You may be able to get around this by giving your UserControl an x:Name attribute and then binding using ElementName and DataContext.PropertyName :

<UserControl x:Name="Root">
    <UserControl.Resouces>
        <Common:EnumDisplayer x:Key="companyTypes"
                      Localizer="{Binding DataContext.CompanyTypeEnumLocalizer, ElementName=Root}" />
    </UserControl.Resouces>
</UserControl>