Applying same interaction trigger to multiple Text

Question

I have multiple textboxes bound to different data, but I would like every one to launch the same command when the TextChanged event is fired. I could copy the interaction line under every textbox but I'm guessing there must be a way to use a template or style to get this working on all of them.

Here is the code for the first textbox

<TextBox Grid.Row="2" Grid.Column="1" Grid.ColumnSpan="3" Height="28" HorizontalAlignment="Stretch" Margin="0,12,12,0" Name="TextBox_Description" VerticalAlignment="Top" TabIndex="3" Text="{Binding Item.Description, ValidatesOnDataErrors=True, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="TextChanged">
                <i:InvokeCommandAction Command="{Binding DataChangedCommand}"/>
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </TextBox>

Answer 1

I'm not positive how to do it with Interaction.Triggers, but in the past I've used the AttachedCommand dependency properties found here and simply used a Style

Normal XAML

<TextBox local:CommandBehavior.Event="TextChanged" 
         local:CommandBehavior.Command="{Binding DataChangedCommand}"/>

Using a Style

<Style TargetType="TextBox">
    <Setter Property="local:CommandBehavior.Event" Value="TextChanged" />
    <Setter Property="local:CommandBehavior.Command" Value="{Binding DataChangedCommand}" />
</Style>

EDIT: Since you can't download files at work, here's the code

CommandBehavior.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Markup;
using System.Windows;
using System.Windows.Input;

// Code to attach a command to any event
// From http://marlongrech.wordpress.com/2008/12/04/attachedcommandbehavior-aka-acb/
namespace Keys.Controls.Helpers.CommandHelpers
{
    /// <summary>
    /// Defines the attached properties to create a CommandBehaviorBinding
    /// </summary>
    public class CommandBehavior
    {
        #region Behavior

        /// <summary>
        /// Behavior Attached Dependency Property
        /// </summary>
        private static readonly DependencyProperty BehaviorProperty =
            DependencyProperty.RegisterAttached("Behavior", typeof(CommandBehaviorBinding), typeof(CommandBehavior),
                new FrameworkPropertyMetadata((CommandBehaviorBinding)null));

        /// <summary>
        /// Gets the Behavior property. 
        /// </summary>
        private static CommandBehaviorBinding GetBehavior(DependencyObject d)
        {
            return (CommandBehaviorBinding)d.GetValue(BehaviorProperty);
        }

        /// <summary>
        /// Sets the Behavior property.  
        /// </summary>
        private static void SetBehavior(DependencyObject d, CommandBehaviorBinding value)
        {
            d.SetValue(BehaviorProperty, value);
        }

        #endregion

        #region Command

        /// <summary>
        /// Command Attached Dependency Property
        /// </summary>
        public static readonly DependencyProperty CommandProperty =
            DependencyProperty.RegisterAttached("Command", typeof(ICommand), typeof(CommandBehavior),
                new FrameworkPropertyMetadata((ICommand)null,
                    new PropertyChangedCallback(OnCommandChanged)));

        /// <summary>
        /// Gets the Command property.  
        /// </summary>
        public static ICommand GetCommand(DependencyObject d)
        {
            return (ICommand)d.GetValue(CommandProperty);
        }

        /// <summary>
        /// Sets the Command property. 
        /// </summary>
        public static void SetCommand(DependencyObject d, ICommand value)
        {
            d.SetValue(CommandProperty, value);
        }

        /// <summary>
        /// Handles changes to the Command property.
        /// </summary>
        private static void OnCommandChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            CommandBehaviorBinding binding = FetchOrCreateBinding(d);
            binding.Command = (ICommand)e.NewValue;
        }

        #endregion

        #region CommandParameter

        /// <summary>
        /// CommandParameter Attached Dependency Property
        /// </summary>
        public static readonly DependencyProperty CommandParameterProperty =
            DependencyProperty.RegisterAttached("CommandParameter", typeof(object), typeof(CommandBehavior),
                new FrameworkPropertyMetadata((object)null,
                    new PropertyChangedCallback(OnCommandParameterChanged)));

        /// <summary>
        /// Gets the CommandParameter property.  
        /// </summary>
        public static object GetCommandParameter(DependencyObject d)
        {
            return (object)d.GetValue(CommandParameterProperty);
        }

        /// <summary>
        /// Sets the CommandParameter property. 
        /// </summary>
        public static void SetCommandParameter(DependencyObject d, object value)
        {
            d.SetValue(CommandParameterProperty, value);
        }

        /// <summary>
        /// Handles changes to the CommandParameter property.
        /// </summary>
        private static void OnCommandParameterChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            CommandBehaviorBinding binding = FetchOrCreateBinding(d);
            binding.CommandParameter = e.NewValue;
        }

        #endregion

        #region Event

        /// <summary>
        /// Event Attached Dependency Property
        /// </summary>
        public static readonly DependencyProperty EventProperty =
            DependencyProperty.RegisterAttached("Event", typeof(string), typeof(CommandBehavior),
                new FrameworkPropertyMetadata((string)String.Empty,
                    new PropertyChangedCallback(OnEventChanged)));

        /// <summary>
        /// Gets the Event property.  This dependency property 
        /// indicates ....
        /// </summary>
        public static string GetEvent(DependencyObject d)
        {
            return (string)d.GetValue(EventProperty);
        }

        /// <summary>
        /// Sets the Event property.  This dependency property 
        /// indicates ....
        /// </summary>
        public static void SetEvent(DependencyObject d, string value)
        {
            d.SetValue(EventProperty, value);
        }

        /// <summary>
        /// Handles changes to the Event property.
        /// </summary>
        private static void OnEventChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            CommandBehaviorBinding binding = FetchOrCreateBinding(d);
            //check if the Event is set. If yes we need to rebind the Command to the new event and unregister the old one
            if (binding.Event != null && binding.Owner != null)
                binding.Dispose();
            //bind the new event to the command if newValue isn't blank (e.g. switching tabs)
            if (e.NewValue.ToString() != "")
                binding.BindEvent(d, e.NewValue.ToString());
        }

        #endregion

        #region Helpers
        //tries to get a CommandBehaviorBinding from the element. Creates a new instance if there is not one attached
        private static CommandBehaviorBinding FetchOrCreateBinding(DependencyObject d)
        {
            CommandBehaviorBinding binding = CommandBehavior.GetBehavior(d);
            if (binding == null)
            {
                binding = new CommandBehaviorBinding();
                CommandBehavior.SetBehavior(d, binding);
            }
            return binding;
        }
        #endregion

    }

}

CommandBehaviorBinding.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Input;
using System.Reflection;
using System.Windows;

// Code to attach a command to any event
// From http://marlongrech.wordpress.com/2008/12/04/attachedcommandbehavior-aka-acb/
namespace Keys.Controls.Helpers.CommandHelpers
{
    /// <summary>
    /// Defines the command behavior binding
    /// </summary>
    public class CommandBehaviorBinding : IDisposable
    {
        #region Properties
        /// <summary>
        /// Get the owner of the CommandBinding ex: a Button
        /// This property can only be set from the BindEvent Method
        /// </summary>
        public DependencyObject Owner { get; private set; }
        /// <summary>
        /// The command to execute when the specified event is raised
        /// </summary>
        public ICommand Command { get; set; }
        /// <summary>
        /// Gets or sets a CommandParameter
        /// </summary>
        public object CommandParameter { get; set; }
        /// <summary>
        /// The event name to hook up to
        /// This property can only be set from the BindEvent Method
        /// </summary>
        public string EventName { get; private set; }
        /// <summary>
        /// The event info of the event
        /// </summary>
        public EventInfo Event { get; private set; }
        /// <summary>
        /// Gets the EventHandler for the binding with the event
        /// </summary>
        public Delegate EventHandler { get; private set; }

        #endregion

        //Creates an EventHandler on runtime and registers that handler to the Event specified
        public void BindEvent(DependencyObject owner, string eventName)
        {
            EventName = eventName;
            Owner = owner;
            Event = Owner.GetType().GetEvent(EventName, BindingFlags.Public | BindingFlags.Instance);
            if (Event == null)
                throw new InvalidOperationException(String.Format("Could not resolve event name {0}", EventName));

            //Create an event handler for the event that will call the ExecuteCommand method
            EventHandler = EventHandlerGenerator.CreateDelegate(
                Event.EventHandlerType, typeof(CommandBehaviorBinding).GetMethod("ExecuteCommand", BindingFlags.Public | BindingFlags.Instance), this);
            //Register the handler to the Event
            Event.AddEventHandler(Owner, EventHandler);
        }

        /// <summary>
        /// Executes the command
        /// </summary>
        public void ExecuteCommand()
        {
            if (Command != null && Command.CanExecute(CommandParameter))
                Command.Execute(CommandParameter);
        }

        #region IDisposable Members
        bool disposed = false;
        /// <summary>
        /// Unregisters the EventHandler from the Event
        /// </summary>
        public void Dispose()
        {
            if (!disposed)
            {
                Event.RemoveEventHandler(Owner, EventHandler);
                disposed = true;
            }
        }

        #endregion
    }
}

EventHandlerGenerator.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection.Emit;
using System.Reflection;

// Code to attach a command to any event
// From http://marlongrech.wordpress.com/2008/12/04/attachedcommandbehavior-aka-acb/
namespace Keys.Controls.Helpers.CommandHelpers
{
    /// <summary>
    /// Generates delegates according to the specified signature on runtime
    /// </summary>
    public static class EventHandlerGenerator
    {
        /// <summary>
        /// Generates a delegate with a matching signature of the supplied eventHandlerType
        /// This method only supports Events that have a delegate of type void
        /// </summary>
        /// <param name="eventInfo">The delegate type to wrap. Note that this must always be a void delegate</param>
        /// <param name="methodToInvoke">The method to invoke</param>
        /// <param name="methodInvoker">The object where the method resides</param>
        /// <returns>Returns a delegate with the same signature as eventHandlerType that calls the methodToInvoke inside</returns>
        public static Delegate CreateDelegate(Type eventHandlerType, MethodInfo methodToInvoke, object methodInvoker)
        {
            //Get the eventHandlerType signature
            var eventHandlerInfo = eventHandlerType.GetMethod("Invoke");
            Type returnType = eventHandlerInfo.ReturnParameter.ParameterType;
            if (returnType != typeof(void))
                throw new ApplicationException("Delegate has a return type. This only supprts event handlers that are void");

            ParameterInfo[] delegateParameters = eventHandlerInfo.GetParameters();
            //Get the list of type of parameters. Please note that we do + 1 because we have to push the object where the method resides i.e methodInvoker parameter
            Type[] hookupParameters = new Type[delegateParameters.Length + 1];
            hookupParameters[0] = methodInvoker.GetType();
            for (int i = 0; i < delegateParameters.Length; i++)
                hookupParameters[i + 1] = delegateParameters[i].ParameterType;

            DynamicMethod handler = new DynamicMethod("", null,
                hookupParameters, typeof(EventHandlerGenerator));

            ILGenerator eventIL = handler.GetILGenerator();

            //load the parameters or everything will just BAM :)
            LocalBuilder local = eventIL.DeclareLocal(typeof(object[]));
            eventIL.Emit(OpCodes.Ldc_I4, delegateParameters.Length + 1);
            eventIL.Emit(OpCodes.Newarr, typeof(object));
            eventIL.Emit(OpCodes.Stloc, local);

            //start from 1 because the first item is the instance. Load up all the arguments
            for (int i = 1; i < delegateParameters.Length + 1; i++)
            {
                eventIL.Emit(OpCodes.Ldloc, local);
                eventIL.Emit(OpCodes.Ldc_I4, i);
                eventIL.Emit(OpCodes.Ldarg, i);
                eventIL.Emit(OpCodes.Stelem_Ref);
            }

            eventIL.Emit(OpCodes.Ldloc, local);

            //Load as first argument the instance of the object for the methodToInvoke i.e methodInvoker
            eventIL.Emit(OpCodes.Ldarg_0);

            //Now that we have it all set up call the actual method that we want to call for the binding
            eventIL.EmitCall(OpCodes.Call, methodToInvoke, null);

            eventIL.Emit(OpCodes.Pop);
            eventIL.Emit(OpCodes.Ret);

            //create a delegate from the dynamic method
            return handler.CreateDelegate(eventHandlerType, methodInvoker);
        }

    }
}

Answer 2

If your UpdateMode is always going to be PropertyChanged then there really isn't any reason not to listen to your own PropertyChangedEvent in your ViewModel. It will definitely improve testability.

    private void OnPropertyChanged(object sender, PropertyChangedEventArgs args)
    {
        switch (args.PropertyName)
        {
            case "Prop1":
            case "Prop2":
                .
                .
                .
                DataChangedCommand.Execute(null);
                break;
        }
    }