[CollectionView] [Windows] memory leaks when ItemsSource has changed

[ivan-todorov-progress]

Description

It seems that the CollectionView is leaking memory every time its ItemsSource property has changed.

Due to a lack of a proper memory profiler on all platforms, I am using a poor man's memory tracker implementation that stores a collection of WeakReferences and observes their IsAlive status:

public static class MemoryTracker
{
    private static readonly List<WeakReference> weakReferences = new List<WeakReference>();

    public static readonly BindableProperty IsTrackedProperty =
        BindableProperty.CreateAttached("IsTracked", typeof(bool), typeof(MemoryTracker),
            false, propertyChanged: OnIsTrackedChanged);

    public static int TotalObjectCount => weakReferences.Count;

    public static int AliveObjectCount => weakReferences.Count(weakReference => weakReference.IsAlive);

    public static bool GetIsTracked(BindableObject bindable)
    {
        return (bool)bindable.GetValue(IsTrackedProperty);
    }

    public static void SetIsTracked(BindableObject bindable, bool isTracked)
    {
        bindable.SetValue(IsTrackedProperty, isTracked);
    }

    private static void OnIsTrackedChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if ((bool)newValue)
        {
            var weakReference = new WeakReference(bindable);

            weakReferences.Add(weakReference);
        }
    }
}

I am using this class to track visual components in XAML like this:

<Grid local:MemoryTracker.IsTracked="True">
    <Label Text="{Binding}" />
</Grid>

I have prepared a small sample project that demonstrates the memory leak.

Note: It is possible that the following bug is related: Memory leaks EVERYWHERE. Since I am describing a somewhat different scenario, I have decided to log a separate bug report for it.

Steps to Reproduce

1. Build and run the sample project in Release build configuration.
2. Click on the "Refresh Memory Info" button to show the initial memory statistics.
3. Click on the "Refresh Items Source" button several times to recreate the collection of items.
4. Click on the "Refresh Memory Info" button to update the memory statistics.
5. Repeat the steps 3 and 4 several times to observe how both total tracked objects and alive objects constantly grow.
6. Click the Recreate Control button to recreate the CollectionView in the visual tree.
7. Click on the "Refresh Memory Info" button to update the memory statistics.
8. Observe how the alive objects are decreased after the CollectionView is recreated.

Note: Clicking the "Refresh Memory Info" button calls the garbage collector forcefully before updating the memory statistics:

GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

Link to public reproduction project repository

https://github.com/ivan-todorov-progress/maui-collection-view-memory-leak-bug

Version with bug

7.0 (current)

Last version that worked well

Unknown/Other

Affected platforms

Windows

Affected platform versions

N/A

Did you find any workaround?

No response

Relevant log output

No response

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[jsuarezruiz]

Could be related with #13327

[jonathanpeppers]

Yes, I think some of these recent fixes might solve this one:

• [controls] fix memory leak in Style and AttachedCollection #13260
• [core] WeakEventManager.RemoveEventHandler() should clear subscriptions #13333
• [core] fix memory leaks in bindings #13327

But I will test this case with main next week.

[LanceMcCarthy]

Thanks for the fast response, Redth and Javier! When you're done reviewing, can you please come back here and let me know which of those items was the culprit? Much appreciated!

[minze-it]

Those leaks are a major issue and an absolute show stopper for our app causing the dotnet-maui version not going live. It would be so great to have those fixes in the next service release of the dotnet 7 version.

[jonathanpeppers]

@ivan-todorov-progress I did indeed find an issue with your sample app above: #13530

Do you know if this only happens on Windows? Android actually seems like it is OK without me changing anything:

[ivan-todorov-progress]

@jonathanpeppers I can confirm this is not happening on Android. My speculation is that on Android the CollectionView clears the BindingContext of its items when they are recycled, so the Bindings get disconnected and we have no memory leak. On Windows it is easily reproducible, however. I have not had the chance to test it with the latest version of Visual Studio and .NET MAUI to see whether the leak is fixed. I'll keep you posted with my findings, once I upgrade.

[ivan-todorov-progress]

@jonathanpeppers I have updated Visual Studio to the latest 17.5 version and re-tested the sample app on all platforms. On Android and iOS there is no memory leak. The memory leak on Windows is still there, though. I believe, we need your fix about ClearLogicalChildren as well: jonathanpeppers@c7837db.

I have updated the bug title and description to make it clear it is a Windows-only issue, in case someone else is tracking this.

P.S.: Great job fixing all these memory-related problems in .NET MAUI!

[JanZeman]

Hello @jonathanpeppers, I know this issue is closed some weeks ago. Nevertheless, can you please shortly comment on my first question on this PR? Does you change fixes ObservableCollection behavior as well?

[JanZeman]

Hi @rmarinho, I can see this fix got merged to release/7.0.2xx. Can you please shortly explain or give reference to the release model? Is there any description that will explain which Visual Studio version will bring this fix to my local environment so I can try to verify and experiment? Thank you very much in advance.