[Android] CollectionView and other control's visibility do not update from Binding

[StepKie]

Description

The Content of a CollectionView bound to a property via DataTemplate will only update when the user interacts with the CollectionView control via a drag gesture. It does not refresh the UI itself via OnPropertyChanged(nameof(BoundProperty)).

Code snippets (reproducible from attached zip)
Test project:

• was created from the default MAUI template
• adding a simple MainViewModel, binding in codebehind of MainPage
• ObservableObject from CommunityToolkit.Mvvm was used as the only dependency for INotifyPropertyChanged (the issue is the same for the Xamarin.CommunityToolkit.MauiCompat version)

<CollectionView ItemsSource="{Binding Items}"
        <CollectionView.ItemTemplate>
          <DataTemplate>
              <Label Text="{Binding .}" />
            </StackLayout>
          </DataTemplate>
        </CollectionView.ItemTemplate>
</CollectionView>

internal class MainPageViewModel : ObservableObject
    {
        private int counter = 0;
        public ObservableCollection<string> Items { get; set; } = new() { "0" };

        public ICommand UpdateItemsCommand => new Command(UpdateItems);

        void UpdateItems()
        {
            Items.Add((++counter).ToString());
            OnPropertyChanged(nameof(Items)); // Not strictly necessary as it is ObservableCollection
        }
    }

Steps to Reproduce

Open the provided TestApp.zip
(edited to include the issue described in #8135 (comment))
TestApp.zip

Click the "Update Icons" button.
It will show that the Items list has been updated.
The UI of the CollectionView will only refresh to show the added items when performing a Drag Gesture (i.e. Click in the CollectionView area below the Label, and drag).

Version with bug

6.0.400 (current)

Last version that worked well

Unknown/Other

Affected platforms

Android, I was not able test on other platforms

Affected platform versions

Android API 30, 31

Did you find any workaround?

No response

Relevant log output

No response

[StepKie]

Also relates maybe to #7747

[jfversluis]

Does it help if you wrap it in a call to run this code on the main thread?

[ghost]

Hi @Hottemax. We have added the "s/needs-info" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[innomarcoItalia]

if it helps, issue that has occurred since version 6.0.400.
This problem is also visible in CollectionView in the project:
https://github.com/dotnet-presentations/dotnet-maui-workshop

[StepKie]

Does it help if you wrap it in a call to run this code on the main thread?

Hi Gerald, I have tried all kinds of Thread magic to get it to work (using AsyncCommand, Task.Delay, ConfigureAwait(false), Device.BeginInvokeOnMainThread(), and a great number of random combinations of these, but nothing yielded any results.
The UI gets notified (as can be observed in the attached sample project by seeing that the LastAdded binding is correctly updated in the UI from the same method, but the CollectionView just refuses to cooperate.

I feel that this should really be high priority, as CollectionView not updating is kind of a deal-breaker.

[StepKie]

Update for platforms:

• Also did not work on physical Android device
• It works on iOS (simulator)
• It works when launching as Windows app

So it really seems to be Android-specific

[StepKie]

Another update:

I don't want to open another ticket for this, so I will add it here, maybe the collectionview tag needs to be removed as the issue seems more general:

The same behavior of UI not updating can be observed when updating other visual elements from a Binding.
I amended the zip File with an example where a Label/ActivityIndicator bind IsVisible to a ViewModel property

TestApp.zip

Observed Behavior:
They correctly appear on iOS and Windows when the Binding updates, but not on Android

Expected Behavior:
They should appear for all platforms

     <Label
        HorizontalOptions="Center"
        IsVisible="{Binding IsBusy}"
        Text="I am only showing for 3 seconds when ShowBusyCommand runs" />
      <ActivityIndicator
        HeightRequest="40"
        HorizontalOptions="FillAndExpand"
        IsEnabled="{Binding IsBusy}"
        IsRunning="{Binding IsBusy}"
        IsVisible="{Binding IsBusy}" />
      <Button
        Command="{Binding ShowBusyCommand}"
        HorizontalOptions="Center"
        Text="Show Activity" />

        public bool IsBusy { get; set; } = false;

        public ICommand ShowBusyCommand => new AsyncCommand(ShowBusyIndicator);

        async Task ShowBusyIndicator()
        {
            // Label and ActivityIndicator will only appear on iOS and Windows, not Android
            IsBusy = true;
            OnPropertyChanged(nameof(IsBusy));
            await Task.Delay(3000);
            IsBusy = false;
            OnPropertyChanged(nameof(IsBusy));
        }

[janseris]

Don't get me wrong, I want you to go over to .NET MAUI and I think that's the right thing to do, but what is stopping you from fixing those bugs and provide PRs? Forms is still maintained, those bugs you mention might not be our (top) priority, but if you say it's important to you I am more than willing to give it a review and add it to the product. You'd be helping yourself and others. And of course that exact same goes for .NET MAUI.

Does seriously a Microsoft employee ask a customer to fix a bug in a Microsoft framework (sounding like it's the customer's responsibility to get it fixed)?
MAUI is not someone's hobby project which we should be helping developing for fun all together.
It is a serious official product like ASP.NET Core, EF Core etc.
Should Windows users also fix bugs which they find in Windows 11 maybe? Can you see how absurd it sounds?

[Symbai]

bind IsVisible to a ViewModel property

That's already trackd in #8044 for which a PR already exist #8136

[hartez]

As @Symbai mentioned, this bug is fixed by PR #8136, which is slated for Service Release 2 (coming soon).