RelayCommand Class for MVVM - C# and VB

Publishing both C# and VB version of the RelayCommand by Josh Smith


Namespace ApplicationClass

''' <summary>

''' A command whose sole purpose is to

''' relay its functionality to other

''' objects by invoking delegates. The

''' default return value for the CanExecute

''' method is 'true'.

''' </summary>

''' <remarks>Class taken from online example. http://msdn.microsoft.com/en-us/magazine/dd419663.aspx Josh Smith</remarks>

Public Class RelayCommand

Implements ICommand

#Region "Fields"

Private ReadOnly _execute As Action(Of Object)

Private ReadOnly _canExecute As Predicate(Of Object)

#End Region

#Region "Constructors"

''' <summary>

''' Creates a new command that can always execute.

''' </summary>

''' <param name="execute">The execution logic.</param>

Public Sub New(ByVal execute As Action(Of Object))

Me.New(execute, Nothing)

End Sub

''' <summary>

''' Creates a new command.

''' </summary>

''' <param name="execute">The execution logic.</param>

''' <param name="canExecute">The execution status logic.</param>

Public Sub New(ByVal execute As Action(Of Object), ByVal canExecute As Predicate(Of Object))

If execute Is Nothing Then

Throw New ArgumentNullException("execute")

End If

_execute = execute

_canExecute = canExecute

End Sub

#End Region

#Region "ICommand Members"

'<DebuggerStepThrough()> _

Public Function CanExecute(ByVal parameter As Object) As Boolean Implements ICommand.CanExecute

Return If(_canExecute Is Nothing, True, _canExecute(parameter))

End Function

Public Custom Event CanExecuteChanged As EventHandler Implements ICommand.CanExecuteChanged

AddHandler(ByVal value As EventHandler)

AddHandler CommandManager.RequerySuggested, value

End AddHandler

RemoveHandler(ByVal value As EventHandler)

RemoveHandler CommandManager.RequerySuggested, value

End RemoveHandler

RaiseEvent(ByVal sender As System.Object, ByVal e As System.EventArgs)

End RaiseEvent

End Event

Public Sub Execute(ByVal parameter As Object) Implements ICommand.Execute

_execute(parameter)

End Sub

#End Region

End Class

End Namespace











using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Windows.Input;

namespace Xpert_Lync.ViewModel

{

public class RelayCommand : ICommand

{

#region Fields

readonly Action<object> _execute;

readonly Predicate<object> _canExecute;

#endregion // Fields

#region Constructors

public RelayCommand(Action<object> execute)

: this(execute, null)

{

}

public RelayCommand(Action<object> execute, Predicate<object> canExecute)

{

if (execute == null)

throw new ArgumentNullException("execute");

_execute = execute;

_canExecute = canExecute;

}

#endregion // Constructors

#region ICommand Members

　

public bool CanExecute(object parameter)

{

return _canExecute == null ? true : _canExecute(parameter);

}

public event EventHandler CanExecuteChanged

{

add { CommandManager.RequerySuggested += value; }

remove { CommandManager.RequerySuggested -= value; }

}

public void Execute(object parameter)

{

_execute(parameter);

}

#endregion // ICommand Members

}

}