EventToCommand.cs

// ****************************************************************************
// <copyright file="EventToCommand.cs" company="GalaSoft Laurent Bugnion">
// Copyright © GalaSoft Laurent Bugnion 2009-2016
// </copyright>
// ****************************************************************************
// <author>Laurent Bugnion</author>
// <email>laurent@galasoft.ch</email>
// <date>3.11.2009</date>
// <project>GalaSoft.MvvmLight.Extras</project>
// <web>http://www.mvvmlight.net</web>
// <license>
// See license.txt in this solution or http://www.galasoft.ch/license_MIT.txt
// </license>
// ****************************************************************************

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

#if SILVERLIGHT
using System.Windows.Controls;
#endif

////using GalaSoft.Utilities.Attributes;

namespace GalaSoft.MvvmLight.Command
{
    /// <summary>
    /// This <see cref="T:System.Windows.Interactivity.TriggerAction`1" /> can be
    /// used to bind any event on any FrameworkElement to an <see cref="ICommand" />.
    /// Typically, this element is used in XAML to connect the attached element
    /// to a command located in a ViewModel. This trigger can only be attached
    /// to a FrameworkElement or a class deriving from FrameworkElement.
    /// <para>To access the EventArgs of the fired event, use a RelayCommand&lt;EventArgs&gt;
    /// and leave the CommandParameter and CommandParameterValue empty!</para>
    /// </summary>
    ////[ClassInfo(typeof(EventToCommand),
    ////  VersionString = "5.2.8",
    ////  DateString = "201504252130",
    ////  Description = "A Trigger used to bind any event to an ICommand.",
    ////  UrlContacts = "http://www.galasoft.ch/contact_en.html",
    ////  Email = "laurent@galasoft.ch")]
    public class EventToCommand : TriggerAction<DependencyObject>
    {
        /// <summary>
        /// Identifies the <see cref="CommandParameter" /> dependency property
        /// </summary>
        public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.Register(
            "CommandParameter",
            typeof(object),
            typeof(EventToCommand),
            new PropertyMetadata(
                null,
                (s, e) =>
                {
                    var sender = s as EventToCommand;
                    if (sender == null)
                    {
                        return;
                    }

                    if (sender.AssociatedObject == null)
                    {
                        return;
                    }

                    sender.EnableDisableElement();
                }));

        /// <summary>
        /// Identifies the <see cref="Command" /> dependency property
        /// </summary>
        public static readonly DependencyProperty CommandProperty = DependencyProperty.Register(
            "Command",
            typeof(ICommand),
            typeof(EventToCommand),
            new PropertyMetadata(
                null,
                (s, e) => OnCommandChanged(s as EventToCommand, e)));

        /// <summary>
        /// Identifies the <see cref="MustToggleIsEnabled" /> dependency property
        /// </summary>
        public static readonly DependencyProperty MustToggleIsEnabledProperty = DependencyProperty.Register(
            "MustToggleIsEnabled",
            typeof(bool),
            typeof(EventToCommand),
            new PropertyMetadata(
                false,
                (s, e) =>
                {
                    var sender = s as EventToCommand;
                    if (sender == null)
                    {
                        return;
                    }

                    if (sender.AssociatedObject == null)
                    {
                        return;
                    }

                    sender.EnableDisableElement();
                }));

        private object _commandParameterValue;

        private bool? _mustToggleValue;

        /// <summary>
        /// Gets or sets the ICommand that this trigger is bound to. This
        /// is a DependencyProperty.
        /// </summary>
        public ICommand Command
        {
            get
            {
                return (ICommand) GetValue(CommandProperty);
            }

            set
            {
                SetValue(CommandProperty, value);
            }
        }

        /// <summary>
        /// Gets or sets an object that will be passed to the <see cref="Command" />
        /// attached to this trigger. This is a DependencyProperty.
        /// </summary>
        public object CommandParameter
        {
            get
            {
                return GetValue(CommandParameterProperty);
            }

            set
            {
                SetValue(CommandParameterProperty, value);
            }
        }

        /// <summary>
        /// Gets or sets an object that will be passed to the <see cref="Command" />
        /// attached to this trigger. This property is here for compatibility
        /// with the Silverlight version. This is NOT a DependencyProperty.
        /// For databinding, use the <see cref="CommandParameter" /> property.
        /// </summary>
        public object CommandParameterValue
        {
            get
            {
                return _commandParameterValue ?? CommandParameter;
            }

            set
            {
                _commandParameterValue = value;
                EnableDisableElement();
            }
        }

        /// <summary>
        /// Gets or sets a value indicating whether the attached element must be
        /// disabled when the <see cref="Command" /> property's CanExecuteChanged
        /// event fires. If this property is true, and the command's CanExecute 
        /// method returns false, the element will be disabled. If this property
        /// is false, the element will not be disabled when the command's
        /// CanExecute method changes. This is a DependencyProperty.
        /// </summary>
        public bool MustToggleIsEnabled
        {
            get
            {
                return (bool) GetValue(MustToggleIsEnabledProperty);
            }

            set
            {
                SetValue(MustToggleIsEnabledProperty, value);
            }
        }

        /// <summary>
        /// Gets or sets a value indicating whether the attached element must be
        /// disabled when the <see cref="Command" /> property's CanExecuteChanged
        /// event fires. If this property is true, and the command's CanExecute 
        /// method returns false, the element will be disabled. This property is here for
        /// compatibility with the Silverlight version. This is NOT a DependencyProperty.
        /// For databinding, use the <see cref="MustToggleIsEnabled" /> property.
        /// </summary>
        public bool MustToggleIsEnabledValue
        {
            get
            {
                return _mustToggleValue == null
                           ? MustToggleIsEnabled
                           : _mustToggleValue.Value;
            }

            set
            {
                _mustToggleValue = value;
                EnableDisableElement();
            }
        }

        /// <summary>
        /// Called when this trigger is attached to a FrameworkElement.
        /// </summary>
        protected override void OnAttached()
        {
            base.OnAttached();
            EnableDisableElement();
        }

#if SILVERLIGHT
        private Control GetAssociatedObject()
        {
            return AssociatedObject as Control;
        }
#else
        /// <summary>
        /// This method is here for compatibility
        /// with the Silverlight version.
        /// </summary>
        /// <returns>The FrameworkElement to which this trigger
        /// is attached.</returns>
        private FrameworkElement GetAssociatedObject()
        {
            return AssociatedObject as FrameworkElement;
        }
#endif

        /// <summary>
        /// This method is here for compatibility
        /// with the Silverlight 3 version.
        /// </summary>
        /// <returns>The command that must be executed when
        /// this trigger is invoked.</returns>
        private ICommand GetCommand()
        {
            return Command;
        }

        /// <summary>
        /// Specifies whether the EventArgs of the event that triggered this
        /// action should be passed to the bound RelayCommand. If this is true,
        /// the command should accept arguments of the corresponding
        /// type (for example RelayCommand&lt;MouseButtonEventArgs&gt;).
        /// </summary>
        public bool PassEventArgsToCommand
        {
            get;
            set;
        }

        /// <summary>
        /// Gets or sets a converter used to convert the EventArgs when using
        /// <see cref="PassEventArgsToCommand"/>. If PassEventArgsToCommand is false,
        /// this property is never used.
        /// </summary>
        public IEventArgsConverter EventArgsConverter
        {
            get;
            set;
        }

        /// <summary>
        /// The <see cref="EventArgsConverterParameter" /> dependency property's name.
        /// </summary>
        public const string EventArgsConverterParameterPropertyName = "EventArgsConverterParameter";

        /// <summary>
        /// Gets or sets a parameters for the converter used to convert the EventArgs when using
        /// <see cref="PassEventArgsToCommand"/>. If PassEventArgsToCommand is false,
        /// this property is never used. This is a dependency property.
        /// </summary>
        public object EventArgsConverterParameter
        {
            get
            {
                return GetValue(EventArgsConverterParameterProperty);
            }
            set
            {
                SetValue(EventArgsConverterParameterProperty, value);
            }
        }

        /// <summary>
        /// Identifies the <see cref="EventArgsConverterParameter" /> dependency property.
        /// </summary>
        public static readonly DependencyProperty EventArgsConverterParameterProperty = DependencyProperty.Register(
            EventArgsConverterParameterPropertyName,
            typeof(object),
            typeof(EventToCommand),
            new PropertyMetadata(null));

        /// <summary>
        /// The <see cref="AlwaysInvokeCommand" /> dependency property's name.
        /// </summary>
        public const string AlwaysInvokeCommandPropertyName = "AlwaysInvokeCommand";

        /// <summary>
        /// Gets or sets a value indicating if the command should be invoked even
        /// if the attached control is disabled. This is a dependency property.
        /// </summary>
        public bool AlwaysInvokeCommand
        {
            get
            {
                return (bool)GetValue(AlwaysInvokeCommandProperty);
            }
            set
            {
                SetValue(AlwaysInvokeCommandProperty, value);
            }
        }

        /// <summary>
        /// Identifies the <see cref="AlwaysInvokeCommand" /> dependency property.
        /// </summary>
        public static readonly DependencyProperty AlwaysInvokeCommandProperty = DependencyProperty.Register(
            AlwaysInvokeCommandPropertyName,
            typeof(bool),
            typeof(EventToCommand),
            new PropertyMetadata(false));


        /// <summary>
        /// Provides a simple way to invoke this trigger programatically
        /// without any EventArgs.
        /// </summary>
        public void Invoke()
        {
            Invoke(null);
        }

        /// <summary>
        /// Executes the trigger.
        /// <para>To access the EventArgs of the fired event, use a RelayCommand&lt;EventArgs&gt;
        /// and leave the CommandParameter and CommandParameterValue empty!</para>
        /// </summary>
        /// <param name="parameter">The EventArgs of the fired event.</param>
        protected override void Invoke(object parameter)
        {
            if (AssociatedElementIsDisabled() 
                && !AlwaysInvokeCommand)
            {
                return;
            }

            var command = GetCommand();
            var commandParameter = CommandParameterValue;

            if (commandParameter == null
                && PassEventArgsToCommand)
            {
                commandParameter = EventArgsConverter == null
                    ? parameter
                    : EventArgsConverter.Convert(parameter, EventArgsConverterParameter);
            }

            if (command != null
                && command.CanExecute(commandParameter))
            {
                command.Execute(commandParameter);
            }
        }

        private static void OnCommandChanged(
            EventToCommand element,
            DependencyPropertyChangedEventArgs e)
        {
            if (element == null)
            {
                return;
            }

            if (e.OldValue != null)
            {
                ((ICommand) e.OldValue).CanExecuteChanged -= element.OnCommandCanExecuteChanged;
            }

            var command = (ICommand) e.NewValue;

            if (command != null)
            {
                command.CanExecuteChanged += element.OnCommandCanExecuteChanged;
            }

            element.EnableDisableElement();
        }

        private bool AssociatedElementIsDisabled()
        {
            var element = GetAssociatedObject();

            return AssociatedObject == null
                || (element != null
                   && !element.IsEnabled);
        }

        private void EnableDisableElement()
        {
            var element = GetAssociatedObject();

            if (element == null)
            {
                return;
            }

            var command = GetCommand();

            if (MustToggleIsEnabledValue
                && command != null)
            {
                element.IsEnabled = command.CanExecute(CommandParameterValue);
            }
        }

        private void OnCommandCanExecuteChanged(object sender, EventArgs e)
        {
            EnableDisableElement();
        }
    }
}