Xamarin.forms: NSRangeException with CollectionView

[davidortinau]

Description

When I bind to a ListView it works, but using CollectionView I get:

Objective-C exception thrown.  Name: NSRangeException Reason: *** -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array

Steps to Reproduce

1. Run the app on iOS and observe the crash

Expected Behavior

Displays a list.

Actual Behavior

Crashes

Basic Information

• Version with issue: 4.0-pre7
  
  
  
  • iOS: 12.1
  
  

Reproduction Link

Archive.zip

[ebvebv]

This is the exception related

{Foundation.MonoTouchException: Objective-C exception thrown.  Name: NSInternalInconsistencyException Reason: Invalid update: invalid number of items in section 0.  The number of items contained in an existing section after the update (1) must be equal to the number of items contained in that section before the update (1), plus or minus the number of items inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out).
Native stack trace:
    0   CoreFoundation                      0x000000011a3961bb __exceptionPreprocess + 331
    1   libobjc.A.dylib                     0x0000000124649735 objc_exception_throw + 48
    2   CoreFoundation                      0x000000011a395f42 +[NSException raise:format:arguments:] + 98
    3   Foundation                          0x0000000118910877 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 194
    4   UIKitCore                           0x0000000129c7b1b7 -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:animator:] + 16010
    5   UIKitCore                           0x0000000129c76fcc -[UICollectionView _updateRowsAtIndexPaths:updateAction:updates:] + 521
    6   UIKitCore                           0x0000000129c77076 -[UICollectionView insertItemsAtIndexPaths:] + 64
    7   ConnectorFiles.iOS                  0x000000010aa3acf9 xamarin_dyn_objc_msgSend + 217
    8   ???                                 0x000000014a6d3467 0x0 + 5543638119
    9   ???                                 0x000000014a578ad4 0x0 + 5542218452
    10  ???                                 0x000000014e9f409b 0x0 + 5614026907
    11  ???                                 0x000000014e9f2bc3 0x0 + 5614021571
    12  ???                                 0x000000014a667716 0x0 + 5543196438

  at ObjCRuntime.Runtime.ThrowNSException (System.IntPtr ns_exception) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.2.1.16/src/Xamarin.iOS/ObjCRuntime/Runtime.cs:398 
  at ObjCRuntime.Runtime.throw_ns_exception (System.IntPtr exc) [0x00000] in /Users/builder/jenkins/workspace/xamarin-macios/xamarin-macios/runtime/Delegates.generated.cs:128 
  at (wrapper native-to-managed) ObjCRuntime.Runtime.throw_ns_exception(intptr)
  at (wrapper managed-to-native) ObjCRuntime.Messaging.void_objc_msgSend_IntPtr(intptr,intptr,intptr)
  at UIKit.UICollectionView.InsertItems (Foundation.NSIndexPath[] indexPaths) [0x00024] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.2.1.16/src/Xamarin.iOS/UIKit/UICollectionView.g.cs:455 
  at Xamarin.Forms.Platform.iOS.ObservableItemsSource.Add (System.Collections.Specialized.NotifyCollectionChangedEventArgs args) [0x00042] in <b5294bb1e836495cae5ff00562d52b34>:0 
  at Xamarin.Forms.Platform.iOS.ObservableItemsSource.CollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs args) [0x00023] in <b5294bb1e836495cae5ff00562d52b34>:0 
  at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00018] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.2.1.16/src/Xamarin.iOS/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:263 
  at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedAction action, System.Object item, System.Int32 index) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.2.1.16/src/Xamarin.iOS/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:338 
  at System.Collections.ObjectModel.ObservableCollection`1[T].InsertItem (System.Int32 index, T item) [0x0001a] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.2.1.16/src/Xamarin.iOS/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:196 
  at System.Collections.ObjectModel.Collection`1[T].Add (T item) [0x00020] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.2.1.16/src/Xamarin.iOS/external/corefx/src/Common/src/CoreLib/System/

[davidortinau]

I finished the Android implementation of my page and CV loads there.

[davidortinau]

This is fixed in 4.0-pre8

[dfarrNTST]

When will pre-8 be released?

[hartez]

Currently scheduled for April 3.

[dfarrNTST]

Thank you. Will UWP support be included or is that down the road?

[hartez]

UWP support is being currently being implemented alongside iOS/Android, but it's behind. So not all features are currently available on all platforms. You can see the current list of supported features here: https://gist.github.com/hartez/7d0edd4182dbc7de65cebc6c67f72e14

And keep in mind that this is still a Preview feature.

[dfarrNTST]

Excellent, thank you for the detailed and quick response. Love the progress info!