Silverlight PRISM Commands – TextChanged

Out of the box the Patterns and Practices PRISM code only supports the click event handler. Writing additional handlers really is very easy. Firstly there are two great starter blogs which I’m not going to recreate:

How Commanding Works in Prism and MVVM by Erik Mork and A code snippet to quickly write Prism commands by Andrea Boschin

Following these patterns it was a sinch to create the code that can be used as a TextChanged command handler:

  1:     public class TextChangedCommandBehavior : CommandBehaviorBase

  2:     {

  3:         public TextChangedCommandBehavior(TextBox targetObject)

  4:             : base(targetObject)

  5:         {

  6:             targetObject.TextChanged += (s, e) => base.ExecuteCommand();

  7:         }

  8:     }

  9: 

 10:     public static class TextChanged

 11:     {

 12:         public static readonly DependencyProperty TextChangedBehaviorProperty =

 13:             DependencyProperty.RegisterAttached(

 14:                 "TextChangedBehavior", typeof(TextChangedCommandBehavior),

 15:                 typeof(TextChangedCommandBehavior), null);

 16: 

 17:         #region CommandProperty

 18: 

 19:         public static readonly DependencyProperty CommandProperty =

 20:             DependencyProperty.RegisterAttached(

 21:                 "Command", typeof(ICommand), typeof(TextChanged),

 22:                 new PropertyMetadata(CommandProperty_Changed));

 23: 

 24:         public static ICommand GetCommand(DependencyObject obj)

 25:         {

 26:             return (ICommand)obj.GetValue(CommandProperty);

 27:         }

 28: 

 29:         public static void SetCommand(DependencyObject obj, ICommand value)

 30:         {

 31:             obj.SetValue(CommandProperty, value);

 32:         }

 33: 

 34:         private static void CommandProperty_Changed(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)

 35:         {

 36:             TextBox targetObject = dependencyObject as TextBox;

 37: 

 38:             if (targetObject != null)

 39:                 GetOrCreateBehavior(targetObject).Command = e.NewValue as ICommand;

 40:         }

 41: 

 42:         #endregion

 43: 

 44:         #region CommandParameterProperty

 45: 

 46:         public static readonly DependencyProperty CommandParameterProperty =

 47:             DependencyProperty.RegisterAttached(

 48:                 "CommandParameter", typeof(object),

 49:                 typeof(TextChanged), new PropertyMetadata(CommandParameterProperty_Changed));

 50: 

 51:         public static ICommand GetCommandParameter(DependencyObject obj)

 52:         {

 53:             return (ICommand)obj.GetValue(CommandParameterProperty);

 54:         }

 55: 

 56:         public static void SetCommandParameter(DependencyObject obj, ICommand value)

 57:         {

 58:             obj.SetValue(CommandParameterProperty, value);

 59:         }

 60: 

 61:         private static void CommandParameterProperty_Changed(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)

 62:         {

 63:             TextBox targetObject = dependencyObject as TextBox;

 64: 

 65:             if (targetObject != null)

 66:                 GetOrCreateBehavior(targetObject).CommandParameter = e.NewValue;

 67:         }

 68: 

 69:         #endregion

 70: 

 71:         private static TextChangedCommandBehavior GetOrCreateBehavior(TextBox targetObject)

 72:         {

 73:             TextChangedCommandBehavior behavior = targetObject.GetValue(TextChangedBehaviorProperty) as TextChangedCommandBehavior;

 74: 

 75:             if (behavior == null)

 76:             {

 77:                 behavior = new TextChangedCommandBehavior(targetObject);

 78:                 targetObject.SetValue(TextChangedBehaviorProperty, behavior);

 79:             }

 80: 

 81:             return behavior;

 82:         }

 83:     }