Windowscommunitytoolkit: [Question] how to show added children in grouped collection // workaround for ObservableGroup immutable key restriction?

[hansmbakker]

I'm trying to build an app that allows modifying a grouped collection (nested ObservableCollection) in a ListView. I am showing the grouped collection in the ListView using a CollectionViewSource.
I am not yet using the ObservableGroup / ObservableGroupedCollection yet, my question is whether they are a viable option.

I would like to achieve the following:

• edit the group names
• edit the individual items
• add / remove new groups
• add / remove individual items

Imagine this (simplified example): having an ObservableCollection<Book>, and every Book has a Title (string) and an ObservableCollection<Uri> for some images.
I want to add books, edit their title, and also add Uris of images and edit them.

• Inside my ListView, I have
  
  
  
  • a GroupStyle with a HeaderTemplate containing
  
  
  • TextBox to edit the Titles
  
  
  • a Button to insert new Uri items --> here is my issue
  
  
  • an ItemTemplate containing a TextBox for the image Uris
  
  
• outside my ListView I have a Button to add new Book items to the ObservableCollection<Book>

With my current solution (ObservableCollection<Book> with Title and ObservableCollection<Uri> inside Book), I can edit Book Titles and Uris, but when I add a new Uri, the ListView does not show it because the CollectionViewSource does not notice it, because the ObservableCollection<Book> does not emit a CollectionChanged event.

This is being discussed in in this StackOverflow item as well.

Then I found ObservableGroup / ObservableGroupedCollection from Windows Community Toolkit, but I'm unsure whether that will solve my issue? Since the Key is immutable I assume they won't let me edit the Book Titles?

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[Kyaa-dost]

@hansmbakker that's a good question. Let me loop in the team and see if anyone will be to assist you with this or tell you if it's feasible with ObservableGroup or ObservableGroupCollection.

[hansmbakker]

Thank you!
As a workaround, I see this probably can be built with nested ListViews, or with a custom ItemsRepeater, but I was wondering what the "proper" way of doing this is.
So I'm curious to hear what they will say.

[hansmbakker]

Also, maybe good to mention @vgromfeld who created these types originally :)
(https://github.com/windows-toolkit/WindowsCommunityToolkit/pull/3201)

[vgromfeld]

@hansmbakker ObservableGroup<TKey, TValue> seems to be a good choice since it provides almost all you need.
The only missing part is to make the ObservableGroup<TKey, TValue>.Key property mutable.
This should be easy to change. ObservableGroup<TKey, TValue> is already inheriting from INotifyPropertyChanged so if you change the Key property to read/write, you can directly raise the property changed event and have the behavior you want.

[hansmbakker]

@vgromfeld thank you for your response!

Are you suggesting to modify the classes in the WCT?

If so, I was wondering whether the read-only setting was meant for a particular requirement or behaviour?

[vgromfeld]

@hansmbakker Yes, you can modify the toolkit classes.

The Key property is read-only because I didn't need it to be writable when I implemented it 😁.

[michael-hawker]

@hansmbakker thanks for raising the issue, did you also want to submit a PR for this change?

[hansmbakker]

Looking at it in more detail now, I see that the ObservableGroup and ObservableGroupedCollection types are sealed.

I want to base two viewmodel types on them, but because of them being sealed I cannot extend them.

Were there any design considerations to add this restriction?

[hansmbakker]

@michael-hawker I'm providing https://github.com/windows-toolkit/WindowsCommunityToolkit/pull/3526 as-is: I'm willing to contribute the changes that unblocked me, and I updated the documentation for it, but I feel not confident in changing the larger picture of this as I am not aware of design considerations that were there when these classes were added.

For example I left ObservableGroupedCollection sealed. Also, I did not update the IReadOnlyObservableGroup because the name suggests it should be immutable.

I want to avoid getting involved in a long-running PR process / ping-ponging this back and forth between me and others; however maintainers have access to the branch in case they want to make modifications to it.