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Catel - Part 4 of n: Unit testing with Catel

, 28 Jan 2011
This article explains how to write unit tests for MVVM using Catel.
Catel-04_01-unittesting.zip
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// --------------------------------------------------------------------------------------------------------------------
// <copyright file="EventToCommand.cs" company="Catel development team">
//   Copyright (c) 2008 - 2011 Catel development team. All rights reserved.
// </copyright>
// <summary>
//   Class to binding any event to a command.
// </summary>
// --------------------------------------------------------------------------------------------------------------------

using System;
using System.Windows;
using System.Windows.Input;
using System.Windows.Interactivity;

namespace Catel.MVVM.Commands
{
    /// <summary>
    /// 
    /// </summary>
    /// <remarks>
    /// This class is based on the implementation of the <c>EventToCommand</c> class that can be found
    /// in the MVVM Light Toolkit (see http://mvvmlight.codeplex.com/).
    /// </remarks>
    public class EventToCommand : TriggerAction<FrameworkElement>
    {
        #region Variables
        #endregion

        #region Constructor & destructor
        #endregion

        #region Properties

        /// <summary>
        /// Gets or sets a value indicating whether the <see cref="EventArgs"/> passed to the event handler
        /// should be passed to the command as well.
        /// </summary>
        /// <value>
        /// 	<c>true</c> if the <see cref="EventArgs"/> passed to the event handler should be passed to the command; otherwise, <c>false</c>.
        /// </value>
        public bool PassEventArgsToCommand { get; set; }

        /// <summary>
        /// Gets or sets a value indicating whether the associated object should be disabled when the command
        /// cannot be executed.
        /// </summary>
        /// <remarks>
        /// Wrapper for the DisableAssociatedObjectOnCannotExecute dependency property.
        /// </remarks>
        public bool DisableAssociatedObjectOnCannotExecute
        {
            get { return (bool)GetValue(DisableAssociatedObjectOnCannotExecuteProperty); }
            set { SetValue(DisableAssociatedObjectOnCannotExecuteProperty, value); }
        }

        /// <summary>
        /// DependencyProperty definition as the backing store for DisableAssociatedObjectOnCannotExecute.
        /// </summary>
        public static readonly DependencyProperty DisableAssociatedObjectOnCannotExecuteProperty =
            DependencyProperty.Register("DisableAssociatedObjectOnCannotExecute", typeof(bool), typeof(EventToCommand), new PropertyMetadata(true,
                (sender, e) => ((EventToCommand)sender).UpdateElementState()));
        
        /// <summary>
        /// Gets or sets the associated Command.
        /// </summary>
        /// <remarks>
        /// Wrapper for the Command dependency property.
        /// </remarks>
        public ICommand Command
        {
            get { return (ICommand)GetValue(CommandProperty); }
            set { SetValue(CommandProperty, value); }
        }

        /// <summary>
        /// DependencyProperty definition as the backing store for Command.
        /// </summary>
        public static readonly DependencyProperty CommandProperty =
            DependencyProperty.Register("Command", typeof(ICommand), typeof(EventToCommand), new PropertyMetadata(null,
                (sender, e) => ((EventToCommand)sender).OnCommandChanged(sender, e)));

        /// <summary>
        /// Gets or sets the command parameter.
        /// </summary>
        /// <remarks>
        /// Wrapper for the CommandParameter dependency property.
        /// </remarks>
        public object CommandParameter
        {
            get { return (object)GetValue(CommandParameterProperty); }
            set { SetValue(CommandParameterProperty, value); }
        }

        /// <summary>
        /// DependencyProperty definition as the backing store for CommandParameter.
        /// </summary>
        public static readonly DependencyProperty CommandParameterProperty =
            DependencyProperty.Register("CommandParameter", typeof(object), typeof(EventToCommand), new PropertyMetadata(null,
                (sender, e) => ((EventToCommand)sender).UpdateElementState()));
        #endregion

        #region Methods
        /// <summary>
        /// Called when the <see cref="Command"/> property has changed.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The <see cref="System.Windows.DependencyPropertyChangedEventArgs"/> instance containing the event data.</param>
        private void OnCommandChanged(object sender, DependencyPropertyChangedEventArgs e)
        {
            if (e.OldValue is ICommand)
            {
                ((ICommand)e.OldValue).CanExecuteChanged -= OnCommandCanExecuteChanged;
            }

            if (e.NewValue is ICommand)
            {
                ((ICommand)e.NewValue).CanExecuteChanged += OnCommandCanExecuteChanged;
            }

            UpdateElementState();
        }

        /// <summary>
        /// Called when the <c>CanExecute</c> state of a command has changed.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
        private void OnCommandCanExecuteChanged(object sender, EventArgs e)
        {
            UpdateElementState();
        }

        /// <summary>
        /// Invokes the action without any parameter.
        /// </summary>
        public void Invoke()
        {
            Invoke(null);
        }

        /// <summary>
        /// Invokes the action.
        /// </summary>
        /// <param name="parameter">The parameter to the action. If the Action does not require a parameter, the parameter may be set to a null reference.</param>
        protected override void Invoke(object parameter)
        {
            if (IsAssociatedObjectDisabled() || (Command == null))
            {
                return;
            }

            object commandParameter = CommandParameter;
            if ((commandParameter == null) && PassEventArgsToCommand)
            {
                commandParameter = parameter;
            }

            if (Command.CanExecute(commandParameter))
            {
                Command.Execute(commandParameter);
            }
        }

        /// <summary>
        /// Checks whether the associated object is disabled or not.
        /// </summary>
        /// <returns><c>true</c> if the associated object is disabled; otherwise <c>false</c>.</returns>
        private bool IsAssociatedObjectDisabled()
        {
#if SILVERLIGHT
            return false;
#else
            return ((AssociatedObject != null) && !AssociatedObject.IsEnabled);
#endif
        }

        /// <summary>
        /// Updates the state of the associated element.
        /// </summary>
        private void UpdateElementState()
        {
            if ((AssociatedObject == null) || (Command == null))
            {
                return;
            }

#if !SILVERLIGHT
            AssociatedObject.IsEnabled = DisableAssociatedObjectOnCannotExecute ? Command.CanExecute(CommandParameter) : true;
            // TODO: Check if we can actually set it to true, or maybe we shouldn't do anything at all
#endif
        }

        /// <summary>
        /// Called when this trigger is attached to a <see cref="FrameworkElement"/>.
        /// </summary>
        protected override void OnAttached()
        {
            base.OnAttached();

            UpdateElementState();
        }
        #endregion
    }
}

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About the Author

Geert van Horrik
Software Developer CatenaLogic
Netherlands Netherlands
I am Geert van Horrik, and I have studied Computer Science in the Netherlands.
 
I love to write software using .NET (especially the combination of WPF and C#). I am also the lead developer of Catel, an open-source application development framework for WPF, Silverlight, WP7 and WinRT with the focus on MVVM.
 
I have my own company since January 1st 2007, called CatenaLogic. This company develops commercial and non-commercial software.
 
To download (or buy) applications I have written, visit my website: http://www.catenalogic.com
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