.NET MAUI RC1 - CollectionView extremely slow

[Sergtek]

Description

Doing some tests with the CollectionView I have realized that the control is extremely slow in .NET Maui, I have added a DataTemplate with several elements to simulate a scenario as close to reality (production environment) and I have realized that something is not It is working well since the more items the ObservableCollection has linked to the ItemsSource and the more items the CollectionView has to render, the slower the application starts, the only thing that occurs to me is that the CollectionView recycling system is not working correctly and render all the CollectionView items at the same time, I have created an identical repository in Xamarin.Forms with 9999 items in the CollectionView and everything works fast and well, however in .NET Maui the same case but only with 300 items takes 2:20 minutes in start the app.

When you go to do the tests, all you have to do is go to the MainPageViewModel class and in the constructor there is a loop that is in charge of initializing the ObservableCollection linked to the CollectionView, by default it is configured in 300 elements, which more or less will do that the app takes about 2:20 seconds to start completely, even when it starts after that time there is a little lag if you try to scroll in the CollectionView until a few seconds pass and the performance stabilizes. I recommend lowering that number to 50 or 100 for faster testing in .NET Maui. In the Xamarin.Forms repository it is set to 9999 items and the performance is perfect and fast, probably because the Xamarin.Forms recycling system works fine.

Loop image:

I leave the 2 GitHub repositories in case you need to do tests:

• .Net Maui:
  https://github.com/nacompllo/MauiCollectionView

• Xamarin.Forms:
  https://github.com/nacompllo/XamarinCollectionView

Steps to Reproduce

Download the attached repository and follow the instructions detailed above.

Version with bug

Release Candidate 1 (current)

Last version that worked well

Unknown/Other

Affected platforms

Android, I was not able test on other platforms

Affected platform versions

Android 10

Did you find any workaround?

No response

Relevant log output

No response

[Dreamescaper]

It will probably work fine if you remove outer VerticalStackLayout.

[Sergtek]

It will probably work fine if you remove outer VerticalStackLayout.

I've tried it but the problem still occurs. I would bet more that it is a problem with the recycling of CollectionView elements since the more items the ItemSource has and the more controls the DataTemplate has the slower the startup is because it probably proceeds to render all the controls of all the items of the CollectionView.

[Dreamescaper]

Ok, I had a similar issue, but caused by the stack layout - it allows collectionView to grow infinitely, and therefore render all the items.
It was closed as not a bug, unfortunately :(

Probably this one is different though, if it didn't help for you.

[Dreamescaper]

Btw, you don't need an outer ScrollLayout either, CollectionView is already scrollable.

[Sergtek]

Ok, I had a similar issue, but caused by the stack layout - it allows collectionView to grow infinitely, and therefore render all the items. It was closed as not a bug, unfortunately :(

Probably this one is different though, if it didn't help for you.

Btw, you don't need an outer ScrollLayout either, CollectionView is already scrollable.

As far as I see something similar has happened to me, since removing the ScrollView works correctly, probably what you said is that with the ScrollView allowed the CollectionView to grow infinitely until all its elements are rendered. This doesn't seem very appropriate, does it make sense for the CollectionView to grow infinitely when it is inside a ScrollView, can this thread be closed, or is it a bug?

[jfversluis]

I think the important thing is here is that it works well in Forms. Then it should also work in .NET MAUI as far as I'm concerned :)

[Sergtek]

Additional note: The CollectionView only grows infinitely when it's inside a ScrollView or VerticalStackLayout. With the rest of the Layouts it does not happen.

[VincentBu]

I try https://github.com/nacompllo/MauiCollectionView on android emulator. It takes about 1 minute to initialize.