WPF TwoWay Binding to a static class Property

Question

There's no problem if Mode=OneWay, but I have this: Class:

namespace Halt
{
    public class ProjectData
    {
            public static string Username {get;set;}
    }
}

And XAML:

xmlns:engine="clr-namespace:Halt.Engine"
<TextBox Name="UsernameTextBox" HorizontalAlignment="Stretch" Margin="10,5,10,0" Height="25"
         Text="{Binding Source={x:Static engine:ProjectData.Username}, Mode=TwoWay}"/>

This dont wanna work because of TwoWay mode. So how to fix it?

Answer 1

Use the static property binding syntax (which is, as far as I know, available since WPF 4.5):

<TextBox Text="{Binding Path=(engine:ProjectData.Username)}"/>

No need to set Mode="TwoWay", as that is the default for the TextBox.Text property anyway.

---

Although not explicitly asked for, you may also want to implement property change notification.

See this answer for how to do it.

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:ProjectData x:Key="projectData"/>
</Window.Resources>
...

<TextBox Name="UsernameTextBox" HorizontalAlignment="Stretch" Margin="10,5,10,0" Height="25"
         Text="{Binding Source={StaticResource projectData}, Path=Username}"/>

Answer 3

When I have to bind to a static property I use a ViewModel that has a property that gets and sets on the static property, for example

public class ProjectData
{
        public static string Username {get;set;}
}

public class ViewModel {
   public string UserName {
      get{ return ProjectData.Username ; }
      set { ProjectData.Username  = value; }
   }
}

Then I set an instance of ViewModel as the UI DataContext.