[iOS] Allow observable source update while CollectionView is not visible #13678

hartez · 2021-02-05T23:25:43Z

Description of Change

Fix timing issue where CollectionView items are added to ObservableSource before CollectionView is visible, and CollectionView is later made visible via Binding.

Issues Resolved

fixes [Bug] Regression: 5.0.0-pre5 often fails to draw dynamically loaded collection view content #13126

API Changes

None

Platforms Affected

iOS

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

Testing Procedure

Automated UI test.

PR Checklist

Targets the correct branch
Tests are passing (or failures are unrelated)

CollectionView updates while CollectionView is hidden; fixes #13126

Tommigun1980 · 2021-02-06T02:35:41Z

Fantastic @hartez! Is there a package with this fix I could test?
Thank you so much!

Only force layout on transition from invisible to visible Move cell size cache to layout and clear cache on size change (e.g., rotation) Use ItemsView size for constraints when possible;

rmarinho · 2021-02-07T22:04:34Z

@Tommigun1980 you can try the packages inside the artifacts folder / Nuget

https://dev.azure.com/xamarin/public/_build/results?buildId=34759&view=artifacts&pathAsName=false&type=publishedArtifacts

https://dev.azure.com/xamarin/6fd3d886-57a5-4e31-8db7-52a1b47c07a8/_apis/build/builds/34759/artifacts?artifactName=nuget&api-version=6.0&%24format=zip

hartez · 2021-02-07T22:43:00Z

UWP and Android test failures are utterly unrelated. iOS 14 failures are the known ListView issues.

Tommigun1980 · 2021-02-08T05:00:49Z

@Tommigun1980 you can try the packages inside the artifacts folder / Nuget

https://dev.azure.com/xamarin/public/_build/results?buildId=34759&view=artifacts&pathAsName=false&type=publishedArtifacts

https://dev.azure.com/xamarin/6fd3d886-57a5-4e31-8db7-52a1b47c07a8/_apis/build/builds/34759/artifacts?artifactName=nuget&api-version=6.0&%24format=zip

Thank you.

Tested with this package and the issue was unfortunately not fixed in my app.

I still have to do the following after populating the CollectionView in order for its items to become visible:

var items = this.myCollectionView.ItemsSource;
this.myCollectionView.ItemsSource = null;
this.myCollectionView.ItemsSource = items;

If I don't do the above, it will display the EmptyView. A hot reload also makes the contents draw properly.

timvandenhof · 2021-02-08T14:14:29Z

@Tommigun1980 you can try the packages inside the artifacts folder / Nuget
https://dev.azure.com/xamarin/public/_build/results?buildId=34759&view=artifacts&pathAsName=false&type=publishedArtifacts
https://dev.azure.com/xamarin/6fd3d886-57a5-4e31-8db7-52a1b47c07a8/_apis/build/builds/34759/artifacts?artifactName=nuget&api-version=6.0&%24format=zip

Thank you.

Tested with this package and the issue was unfortunately not fixed in my app.

I still have to do the following after populating the CollectionView in order for its items to become visible:
var items = this.myCollectionView.ItemsSource;
this.myCollectionView.ItemsSource = null;
this.myCollectionView.ItemsSource = items;
If I don't do the above, it will display the EmptyView. A hot reload also makes the contents draw properly.

We are experiencing the same (or similar) issue, with the same exception. We are using a view with two tabs, where each tabs has a separate view model with separate ObservableCollection. Collection view has grouped items, with sticky list header behaviour disabled.

Downloaded the above NuGet packages and updated locally to verify this issue has been resolved.
This appears not to be the case for us:

Foundation.MonoTouchException: Objective-C exception thrown.  Name: NSInternalInconsistencyException Reason: Invalid update: invalid number of sections.  The number of sections contained in the collection view after the update (12) must be equal to the number of sections contained in the collection view before the update (12), plus or minus the number of sections inserted or deleted (1 inserted, 0 deleted).
Native stack trace:
	0   CoreFoundation                      0x00007fff20421af6 __exceptionPreprocess + 242
	1   libobjc.A.dylib                     0x00007fff20177e78 objc_exception_throw + 48
	2   CoreFoundation                      0x00007fff2042191f +[NSException raise:format:] + 0
	3   Foundation                          0x00007fff2077156a -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 191
	4   UIKitCore                           0x00007fff23d92d24 -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:animator:collectionViewAnimator:] + 15731
	5   UIKitCore                           0x00007fff23d8efa0 -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:animator:] + 60
	6   UIKitCore                           0x00007fff23d8e58e -[UICollectionView _updateSections:updateAction:] + 454
	7   UIKitCore                           0x00007fff23d8e65e -[UICollectionView insertSections:] + 64
	8   UIKit                               0x0000000108ebd4e4 -[UICollectionViewAccessibility insertSections:] + 42
	9   MyApp.iOS                   0x00000001012df489 xamarin_dyn_objc_msgSend + 217
	10  ???                                 0x0000000109a444f0 0x0 + 4456727792

  at ObjCRuntime.Runtime.ThrowNSException (System.IntPtr ns_exception) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/14.8.0.3/src/Xamarin.iOS/ObjCRuntime/Runtime.cs:407
  at ObjCRuntime.Runtime.throw_ns_exception (System.IntPtr exc) [0x00000] in /Users/builder/jenkins/workspace/xamarin-macios/xamarin-macios/runtime/Delegates.generated.cs:126
  at at (wrapper native-to-managed) ObjCRuntime.Runtime.throw_ns_exception(intptr)
  at at (wrapper managed-to-native) ObjCRuntime.Messaging.void_objc_msgSend_IntPtr(intptr,intptr,intptr)
  at UIKit.UICollectionView.InsertSections (Foundation.NSIndexSet sections) [0x0001b] in /Library/Frameworks/Xamarin.iOS.framework/Versions/14.8.0.3/src/Xamarin.iOS/UIKit/UICollectionView.g.cs:537
  at Xamarin.Forms.Platform.iOS.ObservableGroupedSource+<>c__DisplayClass24_0.<Add>b__0 () [0x00000] in D:\agent\1\s\Xamarin.Forms.Platform.iOS\CollectionView\ObservableGroupedSource.cs:207
  at Xamarin.Forms.Platform.iOS.ObservableGroupedSource.Update (System.Action update) [0x00013] in D:\agent\1\s\Xamarin.Forms.Platform.iOS\CollectionView\ObservableGroupedSource.cs:358
  at Xamarin.Forms.Platform.iOS.ObservableGroupedSource.Add (System.Collections.Specialized.NotifyCollectionChangedEventArgs args) [0x00068] in D:\agent\1\s\Xamarin.Forms.Platform.iOS\CollectionView\ObservableGroupedSource.cs:207
  at Xamarin.Forms.Platform.iOS.ObservableGroupedSource.CollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs args) [0x00026] in D:\agent\1\s\Xamarin.Forms.Platform.iOS\CollectionView\ObservableGroupedSource.cs:147
  at Xamarin.Forms.Platform.iOS.ObservableGroupedSource+<>c__DisplayClass19_0.<CollectionChanged>b__0 () [0x00000] in D:\agent\1\s\Xamarin.Forms.Platform.iOS\CollectionView\ObservableGroupedSource.cs:134
  at Foundation.NSAsyncActionDispatcher.Apply () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/14.8.0.3/src/Xamarin.iOS/Foundation/NSAction.cs:152
  at at (wrapper managed-to-native) UIKit.UIApplication.UIApplicationMain(int,string[],intptr,intptr)
  at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Library/Frameworks/Xamarin.iOS.framework/Versions/14.8.0.3/src/Xamarin.iOS/UIKit/UIApplication.cs:86
  at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0000e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/14.8.0.3/src/Xamarin.iOS/UIKit/UIApplication.cs:65
  at MyApp.iOS.Application.Main (System.String[] args) [0x00001] in /Users/MyUsername/Projects/MyApp/MyApp.iOS/Main.cs:16

Tried workarounds:

Make sure update on collection took place on UI thread.
In stead of .Clear(), use a while loop to remove items one by one before adding all new retrieved data.

Maybe the above information is useful for further troubleshooting.

hartez · 2021-02-08T16:40:17Z

@Tommigun1980 I thought it was odd that it didn't work, because I basically just copied your repro project from 13126 as my test case for this. But you're right - applying this nuget package to the repro project does not work.

However, if I apply the nuget package to your repro project and then comment out the using (this.Models.BeginMassUpdate()) in MyViewModel.cs, it does work.

So now I need to figure out what the XamarinUniversity.Infrastructure package's "OptimizedObservableCollection" is doing that's thwarting the ObservableItemsSource.

hartez · 2021-02-08T16:43:37Z

@timvandenhof Your issue sounds like a different problem; your situation is crashing (not just remaining blank) and you're using a grouped collection. Can you open an issue? And if you can provide a small repro project, that would help a lot. It sounds like your problem might be a grouped version of issue #7700.

hartez · 2021-02-08T16:47:35Z

@Tommigun1980 Okay, looking at OptimizedObservableCollection, it looks like when the mass update object is Disposed the collection raises a Reset event. Which should just trigger a full UICollectionView.ReloadData(), but I'm guessing there's a timing/race condition we're not accounting for. I'll add another test case for a reset and see what I can find.

…w is visible;

Tommigun1980 · 2021-02-08T17:19:11Z

@Tommigun1980 Okay, looking at OptimizedObservableCollection, it looks like when the mass update object is Disposed the collection raises a Reset event. Which should just trigger a full UICollectionView.ReloadData(), but I'm guessing there's a timing/race condition we're not accounting for. I'll add another test case for a reset and see what I can find.

Thank you @hartez.

Yeah the OptimizedObservableCollection suspends the updates when it is populated, and only sends out one Reset when done.
It’s effectively a “batch add”.

Thank you so much for fixing these!!

Allow item source updates while CollectionView is hidden; prevent

0ec2206

CollectionView updates while CollectionView is hidden; fixes #13126

Tommigun1980 mentioned this pull request Feb 6, 2021

[Bug] Mega repro project for CollectionView issues here #13231

Open

hartez mentioned this pull request Feb 6, 2021

[Bug] CollectionView does not change from EmptyViewDataTemplate to NonEmptyViewDataTemplate through data template selector from version Xamarin.Forms 4.5 #10831

Closed

Fix bug where measurement cell content is applied to the wrong cell

9a8849b

Only force layout on transition from invisible to visible Move cell size cache to layout and clear cache on size change (e.g., rotation) Use ItemsView size for constraints when possible;

rmarinho requested review from rmarinho and jsuarezruiz February 7, 2021 22:05

jsuarezruiz added a/collectionview p/iOS 🍎 labels Feb 8, 2021

Add test for Reset situation; fix bug with Reset before CollectionVie…

c9fb5ce

…w is visible;

rmarinho approved these changes Feb 9, 2021

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jsuarezruiz approved these changes Feb 9, 2021

View reviewed changes

rmarinho merged commit a10c2c6 into 5.0.0 Feb 9, 2021

rmarinho deleted the fix-13126 branch February 9, 2021 11:54

samhouts added this to the 5.0.0 milestone Feb 12, 2021

samhouts added i/high Completely doesn't work, crashes, or is unusably slow, has no obvious workaround; occurs less often i/regression t/bug 🐛 labels Feb 13, 2021

dependabot bot mentioned this pull request Mar 18, 2021

Bump Xamarin.Forms.Platform.WPF from 4.8.0.1269 to 5.0.0.2012 aleks-ivanov/maui#9

Open

jfversluis mentioned this pull request Feb 4, 2022

[Bug] CollectionView iOS draws both EmptyView and Items/ItemTemplate #13794

Closed

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[iOS] Allow observable source update while CollectionView is not visible #13678

[iOS] Allow observable source update while CollectionView is not visible #13678

hartez commented Feb 5, 2021

Tommigun1980 commented Feb 6, 2021

rmarinho commented Feb 7, 2021 •

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hartez commented Feb 7, 2021 •

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timvandenhof commented Feb 8, 2021

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Tommigun1980 commented Feb 8, 2021

[iOS] Allow observable source update while CollectionView is not visible #13678

[iOS] Allow observable source update while CollectionView is not visible #13678

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hartez commented Feb 5, 2021

Description of Change

Issues Resolved

API Changes

Platforms Affected

Behavioral/Visual Changes

Before/After Screenshots

Testing Procedure

PR Checklist

Tommigun1980 commented Feb 6, 2021

rmarinho commented Feb 7, 2021 • edited Loading

hartez commented Feb 7, 2021 • edited Loading

Tommigun1980 commented Feb 8, 2021 • edited Loading

timvandenhof commented Feb 8, 2021

hartez commented Feb 8, 2021

hartez commented Feb 8, 2021

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Tommigun1980 commented Feb 8, 2021

rmarinho commented Feb 7, 2021 •

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hartez commented Feb 7, 2021 •

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Tommigun1980 commented Feb 8, 2021 •

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