Added db objects are not shown at the Winui3 ItemsControl loading completed.

[daniDevKr]

What happened?

Added db objects are not shown at the Winui3 ItemsControl loading completed.

Repro steps

1. At the ItemsControl control loading sample data are loaded into db.
2. The app window not showing added Realm objects.

Version

net8.0-windows10.0.19041.0

What Atlas Services are you using?

Local Database only

What type of application is this?

Other

Client OS and version

Windows 11 Pro 23H2, build 22631.3958

Code snippets

Sample code repo link: Link

Stacktrace of the exception/crash you're getting

No response

Relevant log output

No response

[sync-by-unito]

➤ PM Bot commented:

Jira ticket: RNET-1173

[uixiu]

I didn't test your linked project.
From reading the MainWindow.xaml and MainWindow.xaml.cs, i think you were binding ItemsControl's ItemsSource to an empty Users[ObservableCollection] , instead of a public/internal _users[IQueryable] getter.

You can bind the ItemsControl's ItemsSource directly to...

public IQueryable Users => _users;

...to leverage collection change notification just like ObservableCollection.

[Sent from mobile app]

[daniDevKr]

Yes, i fix it. But the problem already exist.

[uixiu]

I tested your updated project
Indeed, ItemsControl does not support collection change notifications from Realm's RealmResults collection.
I changed ItemsControl to ItemsRepeater and it correctly reacts to collection change notifications, including Add and Delete.

Here is the updated XAML

<?xml version="1.0" encoding="utf-8"?>
<Window
    x:Class="Winui3ItemsControlBug.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:Winui3ItemsControlBug"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <StackPanel Padding="50">
        <TextBlock> Items:</TextBlock>
        <ItemsRepeater x:Name="ItemsControl1" ItemsSource="{x:Bind _users}" Loaded="ItemsControl1_Loaded">
            <ItemsRepeater.ItemTemplate>
                <DataTemplate x:DataType="local:User">
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{x:Bind Firstname}" Padding="0 0 10 0"/>
                        <TextBlock Text="{x:Bind LastName}"/>
                    </StackPanel>
                </DataTemplate>
            </ItemsRepeater.ItemTemplate>
        </ItemsRepeater>
    </StackPanel>
</Window>

[uixiu]

Hi @daniDevKr ,
I believe this issue has been resolved, as it's not realm-dotnet related. Could you please close this issue if everything looks good?
Thank you!

[daniDevKr]

I replaced IQueryable<User> with IRealmCollection<User> (on repo) because that supports changes notification, by INotifyCollectionChanged event implementation, but not data was showed.
The event IRealmCollection<User>.CollectionChanged was never sended.

[uixiu]

I replaced IQueryable with IRealmCollection (on repo) because that supports changes notification, by INotifyCollectionChanged event implementation, but not data was showed.

In your updated project, you used _users = _db.All<User>().AsRealmCollection();
In fact, you do not need this cast
In the following code doesImplement will be true, which indicates _db.All<User>() impalements IRealmColleciton<User>

private IQueryable<User> _users;
...
public MainWindow()
{
  ...
  bool  doesImplement = _users is IRealmCollection<User>;
  ...
}

The event IRealmCollection.CollectionChanged was never sended.

Try with the following code (taken from https://www.mongodb.com/docs/atlas/device-sdks/sdk/dotnet/react-to-changes/#std-label-dotnet-collection-notifications) to make sure the collection change notifications actually fires ( It correctly fires on a few machines/configs of mine, except for a [v12.0.0-v12.3.0] when compiled under x86 on amd64 Windows machine. So make sure you compile your project against x64).

private IQueryable<User> _users;
...
var subscriptionToken = _users.SubscribeForNotifications((sender, changes) =>
{
    if (changes == null)
    {
      // This is the case when the notification is called
      // for the first time.
      // Populate tableview/listview with all the items
      // from `collection`
      return;
    }
 
    // Handle individual changes
    foreach (var i in changes.DeletedIndices)
    {
      // ... handle deletions ...
    }

    foreach (var i in changes.InsertedIndices)
    {
      // ... handle insertions ...
    }
 
    foreach (var i in changes.NewModifiedIndices)
    {
      // ... handle modifications ...
    }
 
    if (changes.IsCleared)
    {
      // A special case if the collection has been cleared:
      // i.e., all items have been deleted by calling
      // the Clear() method.
    }
    });

Actually the notifications are triggered, which indicate it's not realm-dotnet issue but ItmesControl issue. As I suggested earlier, you can use ItemsRepeater wich will react to collection change (except perhaps range db transactions)

Not all list based controls behaves the same in WinUI. None play correctly with RealmCollection change notification in WPF. You can actually work around this by using the mentionned SubscribeForNotifications to update an auxiliary/proxy ObservableCollection, if that's suiting your needs.