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c# WPF - Custom UserControl with a List as DependencyProperty [duplicate]

I have lots of entities with nested List<> in each.
For example, I have BaseEntity which has List<ColumnEntity>.
ColumnEntity class has List<Info> and so on.
We are working with a WPF UI, and we need to track all changes in every List of BaseEntity. It is implemented by instantiating a new ObservableCollection based on the needed list, and with binding to that ObservableCollection.
What are the pros and cons changing all these nested Lists to ObservableCollections? So we can track all changes in BaseEntity itself without reassigning each list of BaseEntity to modified bound ObservableCollection?
Assuming that methods specific to List are never used.

Interesting question, considering that both List and ObservableCollection implement IList<T> there isn't much of a difference there, ObservableCollection also implements INotifyCollectionChanged interface, which allows WPF to bind to it.
One of the main differences is that ObservableCollection does not have AddRange method, which might have some implications.
Also, I would not use ObservableCollection for places where I know I would not be binding to, for this reason, it is important to go over your design and make sure that you are taking the correct approach in separating layers of concern.
As far as the differences between Collection<T> and List<T> you can have a look here
Generic Lists vs Collection

It depends on exactly what you mean by this:
we need to track all changes in every List of BaseEntity
Would it be enough to track changes to objects already in the list? Or do you need to know when objects are removed from/are added to/change positions within the list?
If a list will contain the same items for their whole lifetime, but the individual objects within that list will change, then it's enough for just the objects to raise change notifications (typically through INotifyPropertyChanged) and List<T> is sufficient. But if the list will contain different objects from time to time, or if the order changes, then you should use ObservableCollection<T>.
So while the differences may be interesting (and a previous poster has already covered those), typically you won't have that much of a choice - either you need ObservableCollection<T> or you don't.

List represents a strongly typed list of objects that can be accessed by index. It provides methods to search, sort, and manipulate lists. The List class is the generic equivalent of the ArrayList class. It implements the IList generic interface using an array whose size is dynamically increased as required.
ObservableCollection is a generic dynamic data collection that uses an interface "INotifyCollectionChanged" to provide notifications when items get added, removed, or when the whole collection is refreshed.
Read more about it in this link: http://www.codeproject.com/Articles/42536/List-vs-ObservableCollection-vs-INotifyPropertyCha

One more important difference is you can access ObservableCollection only from thread on which it was created where as list can be accessed fromany thread.

I see no problem with that, other than a very marginal performance overhead.
Note that if you modify the internal Lists directly, you are not notified about changes. Also if the objects which are contained in the ObservableCollection are modified you are not notified. Notification occurs only, if elements are added, replaced, removed or moved.

Why the ItemsSource in WPF DataGrid IGNORES GetEnumerator() in my bound collection?

I try to implement filtering in my own observable collection.
My approach is following:
I assume the control using ItemsSource should call IEnumerable.GetEnumerator() on my collection to get the items it should render. So I define my own IEnumerable.GetEnumerator() to apply filtering.
Here's relevant code:
public Func<T, bool>? Filter { get; set; }
public void Refresh() {
OnCollectionChanged(
new NotifyCollectionChangedEventArgs(
NotifyCollectionChangedAction.Reset
)
);
}
IEnumerator IEnumerable.GetEnumerator()
=> Filter is null
? (IEnumerator)BaseIEnumerableGetEnumerator.Invoke(this, null)!
: this.Where(Filter).GetEnumerator();
public new IEnumerator<T> GetEnumerator()
=> Filter is null
? base.GetEnumerator()
: this.Where(Filter).GetEnumerator();
private static readonly MethodInfo BaseIEnumerableGetEnumerator
= BaseType.GetMethod(
"System.Collections.IEnumerable.GetEnumerator",
BindingFlags.NonPublic | BindingFlags.Instance
)!;
BTW, my base class is List<T>. It also implements IList, ICollection, INotifyCollectionChanged and INotifyPropertyChanged.
Now - I set the filter.
Nothing happens.
So I call Refresh().
And to my surprise also nothing happens. Why? When Reset is sent to the ItemsCollection - the control should reload, and while reloading it should call GetEnumerator().
I set the breakpoint on my GetEnumerator() method, but it is not called on Refresh. WHY?
To clarify - I try to replicate exact ListCollectionView feature. It contains Refresh() method that applies the filtering.
Another weird thing I see is that my new GetEnumerator() is called by my own control, but it is not called AT ALL by DataGrid.
UPDATE:
As I've recently researched - built-in WPF controls might use some undocumented magic to bind items. They can trigger events on view model objects - that is possible (AFAIK) with Reflection.
IDK, using Reflection in the view you could dig into "underlying System Type" and use it's indexer if it's available to get items. In that case - it would just not use GetEnumerator.
I also checked the source code of ListCollectionView:
https://referencesource.microsoft.com/#PresentationFramework/src/Framework/System/windows/Data/ListCollectionView.cs
It just uses a kind of shadow collection to achieve filtering. Well, that one way to achieve the effect for sure. But the easiest, if not the fastest way to filter any collection is to inject the filter into it's enumeration. No objects are created, no allocations, that should be fast. And easy. It works in my own control, that uses foreach on ItemsSource. It's obvious, foreach calls enumerator. There's no way around it. However, Microsoft's control obviously either don't use foreach or... they operate on something different than just the original items collection.

ItemsControl (including DataGrid, Listbox, etc.) works with the collection not directly, but through ICollectionView.
When a collection does not provide its own ICollectionView implementation (which is almost always the case), the ItemsControl itself creates the most suitable wrapper for it.
Typically, this is a CollectionView and types derived from it.
An example of a class that provides its own wrapper is CompositeCollection.
It provides a wrapper for the CompositeCollectionView.
The CollectionViewSource is also a means to create an ICollectionView for your collection.
Including using the GetDefaultView () method, you can return the default view of your collection.
This is what the ItemsControl uses when you pass your collection to it.
For almost all collections, a ListCollectionView will be a wrapper.
With the resulting wrapper, you can set properties to filter, group, sort, and render the collection view.
If you want to create your own presentation rules for your collection, then you need to implement the ICollectionViewFactory interface.
It has only one CreateView() method that returns the View wrapper for your collection.
You will have to create your own ICollectionView implementation (it's easier to do this based on the CollectionView or ListCollectionView classes).
And then return its instance in the CreateView() method.

OK, DataGrid just doesn't use GetEnumerator to display items.
It uses IList.this[index] and ICollection.Count for that.
So to implement filtering on my collection I had to create a ShadowList that contains filtered items.
Then I provided overrides for IList.this[index] and ICollection.Count to return items from the ShadowList.
Then I updated all adding to my collection to also update the ShadowList if the added item matches the Filter.
It works, however there's a catch: the filtered data is accessible only via IList indexer. So if the consuming control uses it - it will get filtered data, if not - it will get the original data.
I think it's preferable here. My view model needs original collection most of the time, and if it's not the case - I can always apply filter adding .Where(collection.Filter) to the enumerator.
GetEnumerator is called A LOT in a complex view model so it's best if it is the original List<T> enumerator.
The completed collection (ObservableList<T>) is available on GitHub:
https://github.com/HTD/Woof.Windows/blob/master/Woof.Windows.Mvvm/ObservableList.cs

It just uses a kind of shadow collection to achieve filtering.
For the WPF DataGrid, I believe it uses a backing CollectionViewSource, so filtering is a little bit different (as you say, it has a shadow collection).
MSDN has some info on filtering using the WPF DataGrid that I think might be helpful in your case.

updating datagrid with BindingList

I've been looking at the difference between a BindingList and an observablecollection and List. From what I've read, it seems like the BindingList is the only collection type that will notify if an object in it has one of its properties changed. I cannot get this to work.
I have a property on a ViewModel called Matches, which returns a BindingList created out of a list of CarMatch objects in another class. (Cars m_Cars = new Cars();) My DataGrid on the View is bound to this Matches property in the VM.
public BindingList<CarMatch> Matches
{
get
{
Return new BindingList<CarMatch>(m_Cars.Matches);
}
}
Now, in the code I change one of the CarMatch object's properties, say.. automaticTrans = true from false. Matches[0].automaticTrans = true. I want to see that change in the DataGrid. Without implementing INotifyPropertyChanged inside of the CarMatch class, is there a way to update the datagrid from the viewmodel? Using INotifyPropertyChanged on Matches does not seem to do it. There is something about this I just don't understand, and could use an example to look at.

CarMatch (not Matches) has to implement INotifyPropertyChanged. But consider using ObservableCollection unless you really need some of the additional scenarios offered by BindingList: with ObservableCollection, INotifyPropertyChanged comes for free. And, more importantly, BindingList doesn't scale well.

try
dataGrid.Items.Refresh();
but keep in mind that is a expensive call if you have lots of data and you call it several times in a short period of time.

Custom collection that is observable-self sorting-prevents insertions etc

I have a custom type that knows how to compare with others (it implements IComparable), it is working great stored inside an ObservableList.
However there is still somethings lacking in the collection. I am in need of 4 features. A collection that :
Detects duplicates and prevents insertions.
Automatically sorts on every successful insert.
Is observable &
If batches of items are inserted only notifies once the batch is
inserted.
I would like tips on how to make such a collection, what I will need to research/implement etc. I am not looking for code but if you can give that its a bonus.
What I have thought about doing :
Inheriting from ObservableCollection, overriding the add method, checking if the item already exists, if it does ignoring it.
Or
Implementing my own observable collection based off a more generic type like List.

Since you you want to prevent duplicate insertions and you want sorting, a SortedSet might be a good starting position. Since you want notifications, you'll have to extend the standard SortedSet and implement INotifyCollectionChanged and INotifyPropertyChanged. There's an example here and another one here which uses a HashSet instead (which is unordered, but you can easily replace with a SortedSet).
The alternative, which is just as valid, is to go with you first suggestion and extend ObservableCollection.

C# bindinglist made of bindinglists

Is there a simple way to have a bindinglist composed of several bindinglists? i.e. that is the "view" of the lists.
That is to say: I have 3 lists (list1,list2,list3). I want a list that is always the union of the 3 listx (we can suppose that no object is contained in 2 different lists).
Certainly, I can succeed in using the ListChange property but maybe there is a smarter way to do this?

To do this you would need to create your own type, implement IList, IBindingList (and ideally IBindingListView), and optionally ICancelAddNew and IRaiseItemChangedEvents. You'd also need either a public non-object indexer (public T this[int index] {get;}) or ITypedList.
From having done things similar to this, I strongly advise you; don't, unless this is really important. It would be more pragmatic to copy the references into a new BindingList<>.
Also; with new items; which list would it go into?

Have you looked into the CompositeCollection class?
Depending on what you're trying to do, it might help: its purpose is to combine multiple collections into a single collection (typically for display/binding purposes). So, you could create a CompositeCollection and add your three BindingList instances to it. The CompositeCollection will automatically update to include the members of the "child" lists.