Changing the way how the New Action's items list is populated is quite an often task. The default behavior when the current types and all its descendants are added may be inappropriate in large XAF applications with a complex business objects inheritance hierarchy.

That is why we have decided to provide more built-in modes of populating this list. The available modes are listed in the DevExpress.ExpressApp.SystemModule.NewObjectActionItemListMode enumeration.

// ...

public class CustomizeNewActionItemsListController : ObjectViewController<ObjectView, Task> {
    protected override void OnActivated() {
        base.OnActivated();
        NewObjectViewController controller = Frame.GetController<NewObjectViewController>();
        controller.NewObjectActionItemListMode = NewObjectActionItemListMode.LastDescendantsOnly;
    }
}

If none of the default modes meets your requirements, handle the NewObjectViewController.CollectDescendantTypes and NewObjectViewController.CollectCreatableItemTypes events and populate the list manually.

using DevExpress.ExpressApp;
using DevExpress.ExpressApp.SystemModule;
using DevExpress.Persistent.BaseImpl;

// ...

public class CustomizeNewActionItemsListController : ObjectViewController<ObjectView, Task> {
    protected override void OnActivated() {
        base.OnActivated();
        NewObjectViewController controller = Frame.GetController<NewObjectViewController>();
        controller.CollectCreatableItemTypes += HideHCategoryViewController_CollectCreatableItemTypes;
        controller.CollectDescendantTypes += HideHCategoryViewController_CollectDescendantTypes;
        controller.UpdateNewObjectAction();
    }
    private void HideHCategoryViewController_CollectDescendantTypes(object sender, CollectTypesEventArgs e) {
        CustomizeList(e.Types);
    }
    private void HideHCategoryViewController_CollectCreatableItemTypes(object sender, CollectTypesEventArgs e) {
        CustomizeList(e.Types);
    }
    private void CustomizeList(ICollection<Type> types) {
        List<Type> unusableTypes = new List<Type>();
        foreach (Type item in types) {
            if (item == typeof(Task)) {
                unusableTypes.Add(item);
            }
        }
        foreach (Type item in unusableTypes) {
            types.Remove(item);
        }
    }
}