Using static objects in XAML that were created in code in Silverlight

Question

I couldn't get this to work in Silverlight, so I created two test projects. One simple WPF project and one simple Silverlight project that both do only one thing: set a public static readonly variable in code, and use it in a completely bare bones XAML. In WPF, works without a hitch. In Silverlight, I get the following compiler warning and runtime error:

Warning 2 The tag 'Static' does not exist in XML namespace 'http://schemas.microsoft.com/winfx/2006/xaml'...

and

Invalid attribute value {x:Static SilverlightApplication3:Page.Test} for property Text. [Line: 7 Position: 25]

I'm assuming this is not supported in Silverlight 2, or am I just missing something really simple? Here's the full code for both just in case it's the latter:

public partial class Window1 : Window
{
    public static readonly string Test = "test";
    public Window1()
    {
        InitializeComponent();
    }
}

<Window x:Class="WpfApplication4.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300"
        xmlns:WpfApplication4="clr-namespace:WpfApplication4">    
    <Grid>
        <TextBlock Text="{x:Static WpfApplication4:Window1.Test}" />
    </Grid>
</Window>

and here's the SL version:

public partial class Page : UserControl
    {
        public static readonly string Test = "test";
        public Page()
        {
            InitializeComponent();
        }
    }

<UserControl x:Class="SilverlightApplication3.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:SilverlightApplication3="clr-namespace:SilverlightApplication3"
    Width="400" Height="300">
    <Grid x:Name="LayoutRoot" Background="White">
        <TextBlock Text="{x:Static SilverlightApplication3:Page.Test}" />
    </Grid>
</UserControl>

Answer 1

Unfortunately, it looks like Silverlight doesn't support binding to static properties: What is the {x:Static sdfsdf} equivalent?

Answer 2

Unfortunately Silverlight has many limits with respect to functionality and you just found one of them. StaticMarkupExpression is not supported by SL2. You also can't define it by yourself.

e.g. guy from ms: http://blogs.msdn.com/edmaia/archive/2008/11/23/animating-objects-visibility-in-silverlight.aspx

The trick may be to use an object like

class Helper{
    public string Value {get{return Page.Test;}} 

// implement INotifyPropertyChange if you want updates
}

And then

<Grid.Resources>
     <somexmlns:Helper x:Key="Helper"/>
</Grid.Resources>

<TextBlock Text="{Binding Value, Source={StaticResource Helper}}"/>

Answer 3

You can actually bind to static properties as long as the class is not a static class. So using the previous example of the Helper class:

public class Helper { public static string Value{ get {return Page.Test;} } }

The XAML will stay the same.

Answer 4

I just noticed that you had a secondary question about binding to a color. I don't think it can be done in Silverlight. I'm pretty sure the minimum requirement for a binding target in Silverlight is FrameworkElement.

Answer 5

A static object will be instantiated only once and will persist until the end of the program.A static object can retain its state even when it is not in scope, but only visible within their local scope.