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How to sync data in MVVM when using collections

Recently I have started to dig into MVVM to structure a WPF application I am working on. I am struggling to understand how I can keep collections in sync between Model and ViewModel, and in conjunction with that, how to validate information the user will enter.
Suppose I have a (theoretical) class Building, the model, that will store a building layout, during runtime in memory, and otherwise in xml via serialization. Building has a member List, and each entry Floor in that list can have other Lists, like List and List, which could again have members which are Lists (ie. List).
The model:
namespace TestMVVM
{
public class Building
{
public string strName { get; set; }
public List<Floor> floors { get; set; }
}
public class Floor
{
public int iNumber { get; set; }
public List<Room> rooms { get; set; }
}
public class Room
{
public int iSize { get; set; }
public string strName { get; set; }
public List<Door> doors { get; set; }
}
public class Door
{
public bool bIsLocked { get; set; }
}
}
In the View, the List of type Floor will be editable in a DataGrid. The user can enter a new row in the DataGrid to add a Floor to the Building class. In another DataGrid, Rooms could be added to a Floor. This is quite easy when I make all Lists into ObservableCollections, and directly couple them with the View. However, this also means there is no proper separation of concerns, and it gets messy once validation comes into play.
So I wrote a ViewModel class, BuildingViewModel. It will hold a reference to an instance of the model. This is where I run into trouble: the ViewModel will hold an ObservableCollection of type FloorViewModel. But when the user adds an entry, how do I also add an entry to the List in the model? And mostly, keep the data in sync? What if a Room is added to a Floor, or a Door to a Room, how to know where in the Model to update which data? Ie. how to sync nested List member data?
Subsequently I would to make sure no duplicate Floors can be created; ie. if the user adds a floor with a number that is already in the List, the DataGrid must report an error. Same if an existing floor is edited, and same for Room names. I would think that kind of error checking cannot happen within the FloorViewModel class, because it has no access to other instances of itself.
I have searched a lot but found no clear answer to this. It would seem like a rather common situation? Maybe I am simply going in the wrong direction with this?
This is the current ViewModel, where ViewModelBase is a generic class holding implementations of INotifyProretyChanged and INotifyDataErrorInfo.
namespace TestMVVM
{
public class BuildingViewModel : ViewModelBase
{
private Building building;
public string strName
{
get { return building.strName; }
set
{
building.strName = value;
if (value == "") AddError("strName", "Name cannot be empty.");
OnPropertyChanged("strName");
}
}
public ObservableCollection<FloorViewModel> floors
{
// what goes here? how to sync members of floor to the model, and validate data?
}
public BuildingViewModel(Building b)
{
building = b;
}
}
public class FloorViewModel : ViewModelBase
{
public ObservableCollection<Room> rooms
{
// what goes here? how to sync members of room to the right Floor of the model, and validate data?
}
}
// etc
}

There is a problem in the classes, that You provided. Try to apply the law of Demeter, watch this video about how to structure correctly the House object (even same example), than You only call the correct level's addX() method, that will validate.

Look you need to read again MVVM concept.. All the idea is to have one view model per each view. In our situation try this:
namespace TestMVVM
{
public class BuildingViewModel : ViewModelBase
{
private Building building;
private ObservableCollection<Floor> _floors;
public string strName
{
get { return building.strName; }
set
{
//building.strName = value;
if (String.IsNullOrEmpty(value))
{
AddError("strName", "Name cannot be empty.");
return;
}
building.strName = value;
OnPropertyChanged("strName");
}
}
public ObservableCollection<Floor> floors
{
get
{
return _floors;
}
set
{
_floors = value;
}
}
public BuildingViewModel(Building b)
{
building = b;
}
public void AddNewFloor(Floor)
{
// valid your floor
// floors.Add(floor);
}
}
Now I suggest you to add function that will validate your changes in floors and not in the setter of the property.

Or override/create ObservableCollection class and redefine all methods :
public class MyObservableCollection<T> : ICollection<T>, INotifyCollectionChanged, INotifyPropertyChanged
{
public event NotifyCollectionChangedEventHandler CollectionChanged;
public event PropertyChangedEventHandler PropertyChanged;
public int Count { get { return _reference.Count; } }
public bool IsReadOnly { get { return _reference.IsReadOnly; } }
private readonly IList<T> _reference;
public MyObservableCollection(IList<T> reference)
{
_reference = reference;
}
public IEnumerator<T> GetEnumerator()
{
return _reference.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public void Add(T item)
{
_reference.Add(item);
SendNotification();
}
public void Clear()
{
_reference.Clear();
SendNotification();
}
public bool Contains(T item)
{
return _reference.Contains(item);
}
public void CopyTo(T[] array, int arrayIndex)
{
_reference.CopyTo(array, arrayIndex);
}
public bool Remove(T item)
{
var result = _reference.Remove(item);
SendNotification();
return result;
}
private void SendNotification()
{
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(new NotifyCollectionChangedAction()));
}
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("..."));
}
}
}

Why you don't change type (List to ObservableCollection) on Model ?
In this case :
public ObservableCollection<FloorViewModel> floors
{
get{return building.floors;}
}

interconnected lists C#

I have class with two properties which are Lists, one of it contents int - that's IDs of objects from second List. I override setters and getters to save them agreeable with each other. But when I add some this to list they are not synchronized. How to make them synchronized?
Here is code
public class Item
{
private List<Operation> _operations = new List<Operation>();
private List<int> _operationsID = new List<int>();
public List<Operation> operations
{
get { return this._operations; }
set
{
this._operations = value;
if (value != null)
{
foreach (Operation oper in value)
{
this._operationsID.Add(oper.ID);
}
}
}
}
public List<int> operationsID
{
get { return this._operationsID; }
set
{
this._operationsID = value;
if (value != null)
{
foreach (int operID in value)
{
this._operations.Add(new Operation(operID));
}
}
}
}
}
Should I override List.Add if so, how it can me made?

It is a bit unclear what it is you are trying to do, but basically it seems like you need to encapsulate those lists so the user can't work on them directly (and get them out of sync). You do this by not exposing the lists to the user. Basically you are trying to keep the items contained to the user so whenever they work on your set of items, they would be forced to go through this class and the functions that class exposes. Your only issue then is to find out what to expose to the user and in what manner.
public class Item {
private List<Operation> _operations = new List<Operation>();
private List<int> _operationsID = new List<int>();
public void addOperation(Operation o) {
_operations.Add(o);
_operationsID.Add(getIdentifier(o));
}
public void removeOperation(Operation o) {
_operations.Remove(o);
_operationsID.Remove(getIdentifier(o));
}
public void clear() {
_operations.clear();
_operationsID.clear();
}
public void findOperationMatching(Foobar foo) {
//
}
private int getIdentifier(Operation id) {
//
}
}

You have to clear previous list content before calling Add method:
public List<Operation> operations
{
get { return this._operations; }
set
{
this._operations = value;
if (value != null)
{
this._operationsID.Clear();
foreach (Operation oper in value)
{
this._operationsID.Add(oper.ID);
}
}
else
{
this._operationsID = null;
}
}
}
But to be honest, I don't think it's a good idea to keep these things in two different lists. Why don't you use Dictionary<int, Operation>?

It's a bad idea to try to manage two versions of the truth. If it were me, I'd expose one List<Operation> that callers can Add/Remove, and a second IEnumerable<int> which simply exposes the ID's of the operations:
public List<Operation> Operations { get; set; }
public IEnumerable<int> OperationIDs
{
get
{
return Operations.Select(op => op.OperationID);
}
}
This way, callers can use the Operations list to do whatever they need to do (Add, Remove, Count, etc). The OperationIDs is now not a second property that people can work with; instead it only reflects information that is in the Operations property.

Delegates as Properties: Bad Idea?

Consider the following control (snipped for brevity):
public partial class ConfigurationManagerControl : UserControl
{
public Func<string, bool> CanEdit { get; set;}
public Func<string, bool> CanDelete { get; set; }
public Dictionary<string, string> Settings
{
get { return InnerSettings; }
set
{
InnerSettings = value;
BindData();
}
}
private Dictionary<string, string> InnerSettings;
private void OnListIndexChanged(object sender, EventArgs e)
{
this.EditButton.Enabled = false;
this.DeleteButton.Enabled = false;
var indices = this.List.SelectedIndices;
if (indices.Count != 1)
{
return;
}
var index = indices[0];
var item = this.List.Items[index];
if (this.CanEdit != null)
{
this.EditButton.Enabled = this.CanEdit(item.Text);
}
if (this.CanDelete != null)
{
this.DeleteButton.Enabled = this.CanDelete(item.Text);
}
}
}
There's more to this control, but suffice it to say that it allows a user to add, edit, and delete the entries in a Dictionary<string, string>. In order to determine whether or not it should allow the user to edit or delete the entries, it uses the delegate method properties, CanDelete and CanEdit, which are provided by the form or control that hosts it:
public class SetupWizard : Form
{
public SetupWizard()
{
InitializeComponent();
this.SettingManager.CanEdit = CanEditSetting;
this.SettingManager.CanDelete = CanDeleteSetting;
}
private static bool CanEditSetting(string item)
{
var lockedSettings = new[] { "LicenseHash", "ProductHash" };
return !lockedSettings.Contains(item.ToLower());
}
private static bool CanDeleteSetting(string item)
{
var lockedSettings = new[] {
"LicenseHash",
"ProductHash",
"UserName",
"CompanyName"
};
return !lockedSettings.Contains(item.ToLower());
}
}
I find that this design is both satisfactory and worrisome at the same time. On the one hand, it seems to solve the problem using the simplest solution that works (it certainly separates the concerns nicely). On the other hand, I have this nagging concern that I am using delegates improperly and should be using an event, instead (even though I do not need multiple listeners, and only need the caller to tell me if the item is editable).
And then, on the other other hand, there's the chance that there's a completely different design that I haven't even considered that might solve the problem in a vastly superior way.
So. Is this design technically correct, maintainable, and flexible? Or should I be doing something better?

I suggest the use of an interface with these two methods. That's a lot cleaner:
interface ICantThinkOfAGoodName
{
bool CanEdit(string item);
bool CanDelete(string item);
}
You could create something similar to the RelayCommand used in many MVVM frameworks:
public class RelayObject : ICantThinkOfAGoodName
{
public RelayObject() : this(null, null) {}
public RelayObject(Func<string, bool> canEdit, Func<string, bool> canDelete)
{
if(canEdit == null) canEdit = s => true;
if(canDelete == null) canDelete = s => true;
_canEdit = canEdit;
_canDelete = canDelete;
}
public bool CanEdit(string item)
{
return _canEdit(item);
}
public bool CanDelete(string item)
{
return _canDelete(item);
}
}
Use it like this:
public SetupWizard()
{
InitializeComponent();
this.SettingManager.PropertyName = new RelayObject(CanEditSetting,
CanDeleteSetting);
// or (all can be deleted)
this.SettingManager.PropertyName = new RelayObject(CanEditSetting, null);
// or (all can be edited)
this.SettingManager.PropertyName = new RelayObject(null, CanDeleteSetting);
// or (all can be edited and deleted)
this.SettingManager.PropertyName = new RelayObject();
}
BTW: I am using Property injection here, because it is a control. Normally, I would pass the ICantThinkOfAGoodName dependency in the constructor of the ConfigurationManagerControl.

It may be this is what #Daniel Hilgarth is suggesting when he says "use an interface" (n.b. - his answer now reflects a more general/flexible approach to implementing the interface). Instead of assigning delegates to your method directly, why not give the control a property, such as DataState or whatever you want to call it, using an interface that encapsulates the information you need, and leave it up to the owner to decide how to implement that.
interface IDataState
{
bool CanEdit(string item);
bool CanDelete(string item);
}
public partial class ConfigurationManagerControl : UserControl
{
public IDataState DataState {get;set;}
// your code checks DataState.CanEdit & DataState.CanDelete
}
public class SetupWizard : Form, IDataState
{
public SetupWizard()
{
InitializeComponent();
SettingManager.DataState =this;
}
public bool CanEdit(string item)
{
... implement directly or return from your private function
}
public bool CanDelete(string item)
{
}
}
But this gives you the flexibility to implement that interface any way you choose, with another object, etc. and it makes it easy to also just pass the owner itself (implementing the interface).

Limiting what a user can do based on roles

Scenario
I'm building a system where each item gets reviewed by 2 different people. Whenever the first reviewer saves an item review it's then turn for the second checker to complete their individual review. If I submitted the first review and I open the item again then the item is put into a read only state because you can't review your own work. Also, the first reviewer can put the item into a pending state if more information is required, which the second review can't. Each user is given a specific reviewer roll whenever they select an item from a list.
What I have so far
Each time an item is loaded into the editor the person is given one of 2 roles, InitialReviewer or SecondReviewer.
public class Reviewer
{
public void AddReview(string review) { }
}
public class InitialReviewer : Reviewer, ICanPutIntoPendingState
{
public void PutIntoPendingState(string pendingState) { }
}
public class SecondReviewer : Reviewer
{
// Just use base class to add review
}
public class ReviewerService
{
private readonly Reviewer _reviewer;
public void AddReview(string review)
{
_reviewer.AddReview(review);
}
public void PutIntoPendingState(string pendingState)
{
_reviewer.PutIntoPendingState(pendingState);
}
}
A trimmed down version of my editor.
public class Editor
{
private readonly ReviewerService _reviewerService;
public Editor(ReviewerService reviewerService)
{
_reviewerService = reviewerService;
}
public void SaveCommand()
{
if(user chose a pending state && _reviewerService.Reviewer is ICanPutIntoPendingState) // Pending state is a dropdown.
_reviewerService.PutIntoPendingState("pending state");
else // the user made a complete review
_reviewerService.AddReview("user review");
}
}
Problem
The issue I'm having is that I can't seem to escape from having logic inside Save() from the Editor class that doesn't belong there.
Question
How do I rid myself of the logic inside of the Save() function from the Editor class? It appears to be violating the SRP principle. Checking whether the current reviewer object is of type ICanPutIntoPendingState is the big problem, I think.
Note that I've ommited all logic because there's quite a bit.

Woudn't be enough to give to ReviewerService one Save() method, which internaly call one Save() method of, at this point, abstract class Reviewer, whom abstact Save() method's concrete implementation is made in InitialReviewer and SecondReviewer. So you push decisional logic to classes with concrete implementation.
Hope this helps.

Perhaps you should consider moving business logic from Reviewer class to ReviewerService. Simple implementation would be then something like this:
public abstract class Reviewer
{
public abstract bool CanPutIntoPendingState { get; }
}
public class InitialReviewer : Reviewer
{
public override bool CanPutIntoPendingState
{
get
{
return true;
}
}
}
public class SecondReviewer : Reviewer
{
public override bool CanPutIntoPendingState
{
get
{
return false;
}
}
}
public class ReviewerService
{
private readonly Reviewer _reviewer;
public void AddReview(string review)
{
// do add review logic here
}
public void PutIntoPendingState(string pendingState)
{
if (_reviewer.CanPutIntoPendingState )
{
// do PutIntoPendingState logic here
}
}
}
public class Editor
{
private readonly ReviewerService _reviewerService;
public Editor(ReviewerService reviewerService)
{
_reviewerService = reviewerService;
}
public void SaveCommand()
{
if(user chose a pending state) // Pending state is a dropdown.
_reviewerService.PutIntoPendingState("pending state");
else // the user made a complete review
_reviewerService.AddReview("user review");
}
}
You can also consider to expose only one function on reviewer service, that takes input model. Service is then responsible to validate input and take appropriate action. Something like this:
public class ReviewerService
{
private readonly Reviewer _reviewer;
public void StoreReview(ReviewModel model)
{
// validate input here
// do business logic here
if (model.IsPendingState && _reviewer.CanPutIntoPendingState)
{
this.PutIntoPendingState("pending state");
}
else
{
this.AddReview(model.Review);
}
}
private void AddReview(string review)
{
// do add review logic here
}
private void PutIntoPendingState(string pendingState)
{
// do PutIntoPendingState logic here
}
}
public class ReviewModel
{
public string Review { get; set; }
public bool IsPendingState { get; set; }
}
public class Editor
{
private readonly ReviewerService _reviewerService;
public Editor(ReviewerService reviewerService)
{
_reviewerService = reviewerService;
}
public void SaveCommand()
{
ReviewModel model = new ReviewModel() {Review="user review",IsPendingState=user chose a pending state };
_reviewerService.StoreReview(model);
}
}

Opinion wanted: Intercepting changes to lists/collections

Although BindingList<T> and ObservableCollection<T> provide mechanisms to detect list changes, they don't support mechanisms to detect/intercept changes before they happen.
I'm writing a couple of interfaces to support this, but I want to canvas your opinion.
Option 1: Lists raise events for each type of action
Here, consumers might write code like this:
public class Order : Entity
{
public Order()
{
this.OrderItems = new List<OrderItem>();
this.OrderItems.InsertingItem += new ListChangingEventHandler<OrderItem>(OrderItems_InsertingItem);
this.OrderItems.SettingItem += new ListChangingEventHandler<OrderItem>(OrderItems_SettingItem);
this.OrderItems.RemovingItem += new ListChangingEventHandler<OrderItem>(OrderItems_RemovingItem);
}
virtual public List<OrderItem> OrderItems { get; internal set; }
void OrderItems_InsertingItem(object sender, IOperationEventArgs<OrderItem> e)
{
if (!validationPasses)
{
e.Cancel = true;
return;
}
e.Item.Parent = this;
}
void OrderItems_SettingItem(object sender, IOperationEventArgs<OrderItem> e)
{
if (!validationPasses)
{
e.Cancel = true;
return;
}
e.Item.Parent = this;
}
void OrderItems_RemovingItem(object sender, IOperationEventArgs<OrderItem> e)
{
if (!validationPasses)
{
e.Cancel = true;
return;
}
e.Item.Parent = null;
}
}
Option 2: Lists raise a single event, and the action is determined from the event args
Here, consumers might write code like this:
public class Order : Entity
{
public Order()
{
this.OrderItems = new List<OrderItem>();
this.OrderItems.ListChanging += new ListChangingEventHandler<OrderItem>(OrderItems_ListChanging);
}
virtual public List<OrderItem> OrderItems { get; internal set; }
void OrderItems_ListChanging(object sender, IOperationEventArgs<OrderItem> e)
{
switch (e.Action)
{
case ListChangingType.Inserting:
case ListChangingType.Setting:
if (validationPasses)
{
e.Item.Parent = this;
}
else
{
e.Cancel = true;
}
break;
case ListChangingType.Removing:
if (validationPasses)
{
e.Item.Parent = null;
}
else
{
e.Cancel = true;
}
break;
}
}
}
Background: I'm writing a set of general purpose interfaces/classes that represent the core components of DDD, and I'm making the source code available (hence the need to create friendly interfaces).
This question is about making the interface as cohesive as possible, so that consumers can derive and implement their own collections without losing the core semantics.
PS: Please don't suggest using AddXYZ() and RemoveXYZ() methods for each list, because I've already discounted that idea.
PPS: I must include developers using .NET 2.0 :)
Related question.

I would suggest creating something that parallels the ObservableCollection<T> where appropriate. Specifically, I would suggest following the existing techniques for notification of change of collection. Something like:
class MyObservableCollection<T>
: INotifyPropertyChanging, // Already exists
INotifyPropertyChanged, // Already exists
INotifyCollectionChanging, // You'll have to create this (based on INotifyCollectionChanged)
INotifyCollectionChanged // Already exists
{ }
This will follow established patterns so that clients are already familiar with the exposed interfaces-- three of the interfaces already exist. The use of existing interfaces will also allow more proper interaction with other already existing .NET technologies, such as WPF (which binds against the INotifyPropertyChanged and INotifyCollectionChanged interfaces.)
I would expect the INotifyCollectionChanged interface to look something like:
public interface INotifyCollectionChanged
{
event CollectionChangingEventHandler CollectionChanging;
}
public delegate void CollectionChangingEventHandler(
object source,
CollectionChangingEventArgs e
);
/// <remarks> This should parallel CollectionChangedEventArgs. the same
/// information should be passed to that event. </remarks>
public class CollectionChangingEventArgs : EventArgs
{
// appropriate .ctors here
public NotifyCollectionChangedAction Action { get; private set; }
public IList NewItems { get; private set; }
public int NewStartingIndex { get; private set; }
public IList OldItems { get; private set; }
public int OldStartingIndex { get; private set; }
}
If you wish to add cancellation support, simply add a writable bool Cancel property to CollectionChangingEventArgs that the collection will read to determine whether to execute the change that's about to occur.
I suppose this falls under your Option 2. This is the way to go because, to interoperate properly with other .net technologies that monitor changing collections, you're going to have to implement it anyway for INotifyCollectionChanged. This will definitely follow the policy of "Least Surprise" in your interface.

I would recomend seperate events. It seems more clear to me.
EDIT:
You might want to cosider a before and after event such as Inserting,Inserted or as the VB guys have it BeforeInsert, AfterInsert. This will give the user more flexability.

Have a look at this link, maybe that is what you are looking for, a Generic List based object that acts as a List but with built-in events such as BeforeItemAdded, ItemAdded, BeforeItemRemoved, ItemRemoved and ItemsCleared.
Hope this helps, Tom. :)

Actually, you will be surprised how easily you can create a collection like that.
Take a look at System.Collections.ObjectModel.Collection<T>. That is a class which is intended to be used for such things. It has a few virtual methods (one for every operation) which you can override and control very well.
I would recommend Option 1, since it is more clear and straightforward.
Here is an example which you can use for such purposes:
using System;
using System.Collections.ObjectModel;
using System.Collections.Generic;
using System.Linq;
namespace TestGround
{
public class MyCollection<T> : Collection<T>
{
public class ListChangeEventArgs : EventArgs
{
public IEnumerable<T> ItemsInvolved { get; set;}
public int? Index { get; set;}
}
public delegate void ListEventHandler(object sender, ListChangeEventArgs e);
public event ListEventHandler Inserting;
public event ListEventHandler Setting;
public event ListEventHandler Clearing;
public event ListEventHandler Removing;
public MyCollection() : base() { }
public MyCollection(IList<T> innerList) : base(innerList) { }
protected override void ClearItems()
{
Clearing(this, new ListChangeEventArgs()
{
Index = null,
ItemsInvolved = this.ToArray(),
});
base.ClearItems();
}
protected override void InsertItem(int index, T item)
{
Inserting(this, new ListChangeEventArgs()
{
Index = index,
ItemsInvolved = new T[] { item },
});
base.InsertItem(index, item);
}
protected override void RemoveItem(int index)
{
Removing(this, new ListChangeEventArgs()
{
Index = index,
ItemsInvolved = new T[] { this[index] },
});
base.RemoveItem(index);
}
protected override void SetItem(int index, T item)
{
Setting(this, new ListChangeEventArgs()
{
Index = index,
ItemsInvolved = new T[] { item },
});
base.SetItem(index, item);
}
}
}
You could also modify the ListChangeEventArgs to have a bool property with the name "Cancel", and control wheter to do the change or not in the collection.
The after events could also be useful, if you need such functionality.
Of course, you won't have to use all events of every collections, or if it is really necessary, there may be other ways to solve the problem depending on why do you need this functionality.
EDIT:
If you really only want to validate the items and set their Parent property to an entity instance, you can actually write a collection which does exactly that, or something that generalizes the problem in another way. You could pass it a delegate which validates the item, and and another which tells it what to do when an item is added or removed.
For example, you can achieve this using the Action delegate.
You could consume it this way:
class Order : Entity
{
public Order()
{
OrderItems = new MyCollection2<OrderItem>(
//Validation action
item => item.Name != null && item.Name.Length < 20,
//Add action
item => item.Parent = this,
//Remove action
item => item.Parent = null
);
}
...
}
The major benefit of this approach is that you don't have to bother with event handlers or delegates, beacuse all that you need can be written using lambda expressions, however if you need something more advanced, you can always use a real delegate instead of them.
This is an example of the collection:
public class MyCollection2<T> : Collection<T>
{
public Func<T, bool> Validate { get; protected set; }
public Action<T> AddAction { get; protected set; }
public Action<T> RemoveAction { get; protected set; }
public MyCollection2(Func<T, bool> validate, Action<T> add, Action<T> remove)
: base()
{
Validate = Validate;
AddAction = add;
RemoveAction = remove;
}
protected override void ClearItems()
{
foreach (var item in this)
{
RemoveAction(item);
}
base.ClearItems();
}
protected override void InsertItem(int index, T item)
{
if (Validate(item))
{
AddAction(item);
base.InsertItem(index, item);
}
}
protected override void RemoveItem(int index)
{
RemoveAction(this[index]);
base.RemoveItem(index);
}
protected override void SetItem(int index, T item)
{
if (Validate(item))
{
RemoveAction(this[index]);
AddAction(item);
base.SetItem(index, item);
}
}
}
For such purposes, I think this is the cleanest way to go.