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Posted By

bokkers on 03/31/09


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commands WPF MVVM ICommand


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umang_nine


RelayCommand class

 / Published in: C#
 

This class can be found in this article on MSDN: http://msdn.microsoft.com/en-us/magazine/dd419663.aspx#id0090051 It makes it possible to add WPF-commands to your ViewModel classes without the need for using nested classes for each command.

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  1. public class RelayCommand : ICommand
  2. {
  3.     #region Fields
  4.  
  5.     readonly Action<object> _execute;
  6.     readonly Predicate<object> _canExecute;        
  7.  
  8.     #endregion // Fields
  9.  
  10.     #region Constructors
  11.  
  12.     public RelayCommand(Action<object> execute)
  13.     : this(execute, null)
  14.     {
  15.     }
  16.  
  17.     public RelayCommand(Action<object> execute, Predicate<object> canExecute)
  18.     {
  19.         if (execute == null)
  20.             throw new ArgumentNullException("execute");
  21.  
  22.         _execute = execute;
  23.         _canExecute = canExecute;           
  24.     }
  25.     #endregion // Constructors
  26.  
  27.     #region ICommand Members
  28.  
  29.     [DebuggerStepThrough]
  30.     public bool CanExecute(object parameter)
  31.     {
  32.         return _canExecute == null ? true : _canExecute(parameter);
  33.     }
  34.  
  35.     public event EventHandler CanExecuteChanged
  36.     {
  37.         add { CommandManager.RequerySuggested += value; }
  38.         remove { CommandManager.RequerySuggested -= value; }
  39.     }
  40.  
  41.     public void Execute(object parameter)
  42.     {
  43.         _execute(parameter);
  44.     }
  45.  
  46.     #endregion // ICommand Members
  47. }
  48.  
  49. // To use this class within your viewmodel class:
  50. RelayCommand _myCommand;
  51. public ICommand MyCommand
  52. {
  53.     get
  54.     {
  55.         if (_myCommand == null)
  56.         {
  57.             _myCommand = new RelayCommand(p => this.DoMyCommand(p),
  58.                 p => this.CanDoMyCommand(p) );
  59.         }
  60.         return _myCommand;
  61.     }
  62. }

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