wpf - binding datacontext to static properties of singleton class

Question

I found myself using a lot of individual bindings to my App class for storage of properties and this led me to a untracable stackoverflow exception. I've now decided I would move those properties to a separate singleton ApplicationInfo class but I am having some issues with the binding.

If I bind directly to a member property of my class, such as CurrentUser then it works fine. But when I try to bind a datacontext to this class I get compiler errors and I am sure there is some simple modification that i've overlooked.

I've created a singleton out of this class but now when I try to compile I get the error "Unknown build error - key cannot be null" and it points to my Datacontext binding for the error message.

Here's my class:

 public class ApplicationInfo
{
    private ApplicationInfo()
    {

    }
    private static ApplicationInfo _Current = new ApplicationInfo();
    public static  ApplicationInfo Current
    {
        get { return _Current; }         
    }

    #region Application Info Properties
    private static Assembly _ExecutingAssembly = System.Reflection.Assembly.GetExecutingAssembly();  //holds a copy of this app's assembly info
    public static String ApplicationName
    {
        get { return _ExecutingAssembly.ManifestModule.Name; }
    }
    public static String ApplicationNameTrimmed
    {
        get { return _ExecutingAssembly.ManifestModule.Name.TrimEnd('.', 'e', 'x'); }
    }
    public static String ApplicationPath
    {
        get { return _ExecutingAssembly.Location; }
    }
    public static String ApplicationVersion
    {
        get { return _ExecutingAssembly.GetName().Version.ToString(); }
    }
    public static DateTime ApplicationCompileDate
    {
        get { return File.GetCreationTime(Assembly.GetExecutingAssembly().Location); }
    }
    #endregion
    private static Boolean _hasOpenWindows;
    public static Boolean HasOpenWindows
    {
        get { return _hasOpenWindows; }
        set { _hasOpenWindows = value; }
    }

    private static User _currentuser;
    public static User CurrentUser
    {
        get { return _currentuser; }
        set { _currentuser = value; }
    }
    private static Mantissa.DAL _datalayer;
    public static Mantissa.DAL DataLayer
    {
        get { return _datalayer; }
        set { _datalayer = value; }
    }
    private static string _connectionstring;
    public static string ConnectionString
    {
        get { return _connectionstring; }
        set { _connectionstring = value; }
    }





}

This works:

`Title="{Binding Source={x:Static my:ApplicationInfo.ApplicationNameTrimmed}}"`

This does not: (throws the key cannot be null msg)

DataContext="{Binding Source={x:Static my:ApplicationInfo.Current}}"

But when I put the same property in my App class then this works:

  DataContext="{Binding Source={x:Static Application.Current}}"

so how do I fix this?

Answer 1

x:Static is used to get static fields and properties. ApplicationInfo is a class, not a property. To bind, you must either create an instance of it and use its instance property, or bind to a static property (accessing it doesn't require instances).

If you want to bind to a specific property, use Title="{Binding Source={x:Static my:ApplicationInfo.ApplicationNameTrimmed}}".

If you want to set DataContext and then to use bindings to other properties, use DataContext="{Binding Source={x:Static my:ApplicationInfo.Current}}" and convert static properties to instance properties (remove static keyword). You'll also be able to bind like this: Title="{Binding Source={x:Static my:ApplicationInfo.Current.ApplicationNameTrimmed}}".

Current property is usually named Instance, by the way.