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copied!<p>Stale questions deserve fresh answers :)</p> <p>Deriving a class from <code>ListCollectionView</code> is the path I took to control the objects being added by <code>AddNew</code> as well, but after browsing through the source of <code>ListCollectionView</code> to find out what it does internally, I found that the safest way to redefine <code>AddNew</code> (it's not technically an override) is to use <code>ListCollectionView.AddNewItem</code> after creating my new object, so your code would look like this:</p> <pre><code>public class CustomView : ListCollectionView, IEditableCollectionView { public CustomView(System.Collections.IList list) : base(list) { } object IEditableCollectionView.AddNew() { DerivedB obj = new DerivedB(); return base.AddNewItem(obj); } } </code></pre> <p>This works well because, in addition to having nearly identical implementations otherwise, <code>ListCollectionView.AddNew()</code> and <code>ListCollectionView.AddNewItem(object item)</code> both call <code>AddNewCommon(object newItem)</code>:</p> <pre><code> public object AddNew() { VerifyRefreshNotDeferred(); if (IsEditingItem) { CommitEdit(); // implicitly close a previous EditItem } CommitNew(); // implicitly close a previous AddNew if (!CanAddNew) throw new InvalidOperationException(SR.Get(SRID.MemberNotAllowedForView, "AddNew")); return AddNewCommon(_itemConstructor.Invoke(null)); } public object AddNewItem(object newItem) { VerifyRefreshNotDeferred(); if (IsEditingItem) { CommitEdit(); // implicitly close a previous EditItem } CommitNew(); // implicitly close a previous AddNew if (!CanAddNewItem) throw new InvalidOperationException(SR.Get(SRID.MemberNotAllowedForView, "AddNewItem")); return AddNewCommon(newItem); } </code></pre> <p><code>AddNewCommon</code> is where all the real magic happens; firing events, calling <code>BeginInit</code> and <code>BeginEdit</code> on the new item if supported, and eventually through callbacks on the datagrid, establishing the cell bindings:</p> <pre><code> object AddNewCommon(object newItem) { _newItemIndex = -2; // this is a signal that the next Add event comes from AddNew int index = SourceList.Add(newItem); // if the source doesn't raise collection change events, fake one if (!(SourceList is INotifyCollectionChanged)) { // the index returned by IList.Add isn't always reliable if (!Object.Equals(newItem, SourceList[index])) { index = SourceList.IndexOf(newItem); } BeginAddNew(newItem, index); } Debug.Assert(_newItemIndex != -2 && Object.Equals(newItem, _newItem), "AddNew did not raise expected events"); MoveCurrentTo(newItem); ISupportInitialize isi = newItem as ISupportInitialize; if (isi != null) { isi.BeginInit(); } IEditableObject ieo = newItem as IEditableObject; if (ieo != null) { ieo.BeginEdit(); } return newItem; } </code></pre> <p>Here I've included the source code to my <code>TypedListCollectionView</code>, which I use to control the <code>AddNew</code> behavior when I don't know what type will be needed at design time:</p> <pre><code> public class TypedListCollectionView : ListCollectionView, IEditableCollectionView { Type AddNewType { get; set; } public TypedListCollectionView(System.Collections.IList source, Type addNewType) : base(source) { AddNewType = addNewType; } object IEditableCollectionView.AddNew() { object newItem = Activator.CreateInstance(AddNewType); return base.AddNewItem(newItem); } } </code></pre> <p>I like this approach since it provides maximum flexibility for cases where <code>AddNew</code>'s type may need to be adjusted at runtime from one to another. It also allows <code>AddNew</code> to work for adding the first item in the collection, which is handy when the list source is initially empty, but its underlying type can be determined.</p> <p><a href="http://social.msdn.microsoft.com/Forums/en/wpf/thread/381dfbbd-1e9a-4a79-8a40-87b4d8767264" rel="nofollow">This link</a> discusses an alternative way to force the type used by <code>AddNew()</code>. It uses reflection to set the private <code>_itemConstructor</code> property used by <code>AddNew</code> to a parameterless constructor of a specified type. This would be particularly useful when your <code>ListCollectionView</code> is coming from a component that's outside of your influence, or you need to add functionality into existing code and you're worried about breaking things (which I never am because I'm a cavalier coder who callously carouses with collections).</p>

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