Binding to static property

Question

I m having a hard time binding a simple static string property to a TextBox    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 TextBox    lt TextBox gt       lt TextBox Text gt           lt Binding Source   x Static local VersionManager FilterString    gt       lt  TextBox Text gt   lt  TextBox gt    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

User · Answer

Leanest answer   net 4 5 and later        static public event EventHandler FilterStringChanged      static string  filterString      static public string FilterString               get   return  filterString            set                        filterString  value              FilterStringChanged  Invoke null  EventArgs Empty                     and XAML        lt TextBox Text   Binding Path  local VersionManager FilterString     gt    Don t neglect the brackets

User · Answer

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   lt Window Resources gt       lt local VersionManager x Key  quot versionManager quot   gt   lt  Window Resources gt        lt TextBox Text  quot  Binding Source  StaticResource versionManager   Path FilterString  quot   gt

User · Answer

If you are using local resources you can refer to them as below    lt TextBlock Text   Binding Source  x Static prop Resources PerUnitOfMeasure    TextWrapping  Wrap  TextAlignment  Center   gt

User · Answer

Right variant for  NET 4 5    C  code  public class VersionManager       private static string filterString       public static string FilterString               get   gt  filterString          set                       if  filterString    value                  return               filterString   value               StaticPropertyChanged  Invoke null  FilterStringPropertyEventArgs                        private static readonly PropertyChangedEventArgs FilterStringPropertyEventArgs   new PropertyChangedEventArgs  nameof FilterString        public static event PropertyChangedEventHandler StaticPropertyChanged      XAML binding  attention to braces they are     not       lt TextBox Text   Binding Path  yournamespace VersionManager FilterString      gt

User · Answer

Another solution is to create a normal class which implements PropertyChanger like this  public class ViewProps   PropertyChanger       private string  MyValue   string Empty      public string MyValue               get                return  MyValue                   set                       if   MyValue    value                                return                            SetProperty ref  MyValue  value                       Then create a static instance of the class somewhere you wont  public class MyClass       private static ViewProps  ViewProps   null      public static ViewProps ViewProps               get                       if   ViewProps    null                                 ViewProps   new ViewProps                              return  ViewProps                      And now use it as static property   lt TextBlock  Text   x Bind local MyClass ViewProps MyValue  Mode OneWay      gt    And here is PropertyChanger implementation if necessary  public abstract class PropertyChanger   INotifyPropertyChanged       public event PropertyChangedEventHandler PropertyChanged       protected bool SetProperty lt T gt  ref T storage  T value   CallerMemberName  string propertyName   null                if  object Equals storage  value   return false           storage   value          OnPropertyChanged propertyName           return true             protected void OnPropertyChanged  CallerMemberName  string propertyName   null                PropertyChanged  Invoke this  new PropertyChangedEventArgs propertyName

User · Answer

These answers are all good if you want to follow good conventions but the OP wanted something simple  which is what I wanted too instead of dealing with GUI design patterns  If all you want to do is have a string in a basic GUI app you can update ad-hoc without anything fancy  you can just access it directly in your C  source   Let s say you ve got a really basic WPF app MainWindow XAML like this     lt Window x Class  MyWPFApp MainWindow              xmlns  http   schemas microsoft com winfx 2006 xaml presentation              xmlns x  http   schemas microsoft com winfx 2006 xaml              xmlns d  http   schemas microsoft com expression blend 2008              xmlns mc  http   schemas openxmlformats org markup-compatibility 2006              xmlns local  clr-namespace MyWPFApp              mc Ignorable  d              Title  MainWindow              Height  200              Width  400              Background  White   gt       lt Grid gt           lt TextBlock x Name  textBlock                                            Text                             HorizontalAlignment  Center                         VerticalAlignment  Top                         FontWeight  Bold                         FontFamily  Helvetica                         FontSize  16                         Foreground  Blue  Margin  0 10 0 0                 gt           lt Button x Name  Find Kilroy                      Content  Poke Kilroy                      Click  Button Click Poke Kilroy                      HorizontalAlignment  Center                      VerticalAlignment  Center                      FontFamily  Helvetica                      FontWeight  Bold                      FontSize  14                      Width  280                gt       lt  Grid gt   lt  Window gt    That will look something like this     In your MainWindow XAML s source  you could have something like this where all we re doing in changing the value directly via textBlock Text s get set functionality   using System Windows   namespace MyWPFApp       public partial class MainWindow   Window               public MainWindow     InitializeComponent               private void Button Click Poke Kilroy object sender  RoutedEventArgs e                        textBlock Text                         r n                                                 o o   r n                                  ----ooO-     -Ooo----                       Then when you trigger that click event by clicking the button  voila  Kilroy appears

User · Answer

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  Define app below to be the namespace  and assembly  location of the VersionManager class    lt TextBox Text   x Static app VersionManager FilterString     gt    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               lt TextBox Text   Binding Source  x Static local VersionManager Instance                           Path FilterString    gt

User · Answer

There could be two ways syntax to bind a static property  If p is a static property in class MainWindow  then binding for textbox will be   1    lt TextBox Text   x Static local MainWindow p     gt    2    lt TextBox Text   Binding Source  x Static local MainWindow p  Mode OneTime     gt

User · Answer

In  NET 4 5 it s possible to bind to static properties  read more     You can use static properties as the source of a data binding  The   data binding engine recognizes when the property s value changes if a   static event is raised  For example  if the class SomeClass defines a   static property called MyProperty  SomeClass can define a static event   that is raised when the value of MyProperty changes  The static event   can use either of the following signatures    public static event EventHandler MyPropertyChanged   public static event EventHandler lt PropertyChangedEventArgs gt  StaticPropertyChanged        Note that in the first case  the class exposes a static event named   PropertyNameChanged that passes EventArgs to the event handler     In the second case  the class exposes a static event named   StaticPropertyChanged that passes PropertyChangedEventArgs to the   event handler  A class that implements the static property can choose   to raise property-change notifications using either method

User · Answer

As of WPF 4 5 you can bind directly to static properties and have the binding automatically update when your property is changed  You do need to manually wire up a change event to trigger the binding updates   public class VersionManager       private static String  filterString                    lt summary gt          A static property which you d like to bind to          lt  summary gt      public static String FilterString               get                       return  filterString                     set                        filterString   value                  Raise a change event             OnFilterStringChanged EventArgs Empty                           Declare a static event representing changes to your static property     public static event EventHandler FilterStringChanged          Raise the change event through this static method     protected static void OnFilterStringChanged EventArgs e                EventHandler handler   FilterStringChanged           if  handler    null                        handler null  e                        static VersionManager                    Set up an empty event handler         FilterStringChanged     sender  e    gt    return                You can now bind your static property just like any other    lt TextBox Text   Binding Path  local VersionManager FilterString     gt

User · Answer

You can use ObjectDataProvider class and it s MethodName property  It can look like this    lt Window Resources gt      lt ObjectDataProvider x Key  versionManager  ObjectType   x Type VersionManager   MethodName  get FilterString  gt  lt  ObjectDataProvider gt   lt  Window Resources gt    Declared object data provider can be used like this    lt TextBox Text   Binding Source  StaticResource versionManager      gt

User · Answer

Look at my project CalcBinding  which provides to you writing complex expressions in Path property value  including static properties  source properties  Math and other  So  you can write this    lt TextBox Text   c Binding local VersionManager FilterString    gt    Goodluck

[wpf] Binding to static property

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