Problem binding to static property

Question

I'm having a hard time binding a simple static string property to a text box.

Here's the class with the static property:

public class VersionManager
{
    private static string filterString;

    public static string FilterString
    {
        get { return filterString; }
        set { filterString = value; }
    }
}

In my xaml, I just want to bind this static property to a text box:

<TextBox>
    <TextBox.Text>
        <Binding Source="{x:Static local:VersionManager.FilterString}"/>
    </TextBox.Text>
</TextBox>

Everything compiles, but at run time, I get the following exception:

Cannot convert the value in attribute 'Source' to object of type 'System.Windows.Markup.StaticExtension'. Error at object 'System.Windows.Data.Binding' in markup file 'BurnDisk;component/selectversionpagefunction.xaml' Line 57 Position 29.

Any idea what I'm doing wrong?

Answer 1

You can't bind to a static like that. There's no way for the binding infrastructure to get notified of updates since there's no DependencyObject (or object instance that implement INotifyPropertyChanged) involved.

If that value doesn't change, just ditch the binding and use x:Static directly inside the Text property.

If the value does change, I'd suggest creating a singleton to contain the value and bind to that.

An example of the singleton:

public class VersionManager : DependencyObject {
    public static readonly DependencyProperty FilterStringProperty =
        DependencyProperty.Register( "FilterString", typeof( string ),
        typeof( VersionManager ), new UIPropertyMetadata( "no version!" ) );
    public string FilterString {
        get { return (string) GetValue( FilterStringProperty ); }
        set { SetValue( FilterStringProperty, value ); }
    }

    public static VersionManager Instance { get; private set; }

    static VersionManager() {
        Instance = new VersionManager();
    }
}


<TextBox Text="{Binding Source={x:Static local:VersionManager.Instance}, Path=FilterString}"></TextBox>

Answer 2

If the binding needs to be two-way, you must supply a path. There's a trick to do two-way binding on a static property, provided the class is not static : declare a dummy instance of the class in the resources, and use it as the source of the binding.

<Window.Resources>
    <local:VersionManager x:Key="versionManager"/>
</Window.Resources>
...

<TextBox Text="{Binding Source={StaticResource versionManager}, Path=FilterString}"/>