Bug 55745 - [iOS] NRE in ListView with HasUnevenRows=true after changing content and rebinding
Summary: [iOS] NRE in ListView with HasUnevenRows=true after changing content and rebi...
Alias: None
Product: Forms
Classification: Xamarin
Component: iOS ()
Version: 2.3.5
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Jimmy [MSFT]
Depends on:
Reported: 2017-04-28 19:39 UTC by otyq08
Modified: 2017-06-29 12:00 UTC (History)
6 users (show)

Tags: ios crash listview labelrenderer ac
Is this bug a regression?: Yes
Last known good build: Forms 2.3.4

Simple project for reproduction. (296.04 KB, application/x-zip-compressed)
2017-04-28 19:39 UTC, otyq08

Notice (2018-05-24): bugzilla.xamarin.com is now in read-only mode.

Please join us on Visual Studio Developer Community and in the Xamarin and Mono organizations on GitHub to continue tracking issues. Bugzilla will remain available for reference in read-only mode. We will continue to work on open Bugzilla bugs, copy them to the new locations as needed for follow-up, and add the new items under Related Links.

Our sincere thanks to everyone who has contributed on this bug tracker over the years. Thanks also for your understanding as we make these adjustments and improvements for the future.

Please create a new report on Developer Community or GitHub with your current version information, steps to reproduce, and relevant error messages or log files if you are hitting an issue that looks similar to this resolved bug and you do not yet see a matching new report.

Related Links:

Description otyq08 2017-04-28 19:39:48 UTC
Created attachment 21893 [details]
Simple project for reproduction.

NullReferenceException occurs after two simple operations in the ListView. First clear the list and add a item. Then clear and bind to a new ObservableCollection with previous content.

 	0x51 in UIKit.UIApplication.UIApplicationMain	C#
 	0xB in UIKit.UIApplication.Main at /Users/builder/data/lanes/4466/a04678c2/source/xamarin-macios/src/UIKit/UIApplication.cs:79,4	C#
 	0x3B in UIKit.UIApplication.Main at /Users/builder/data/lanes/4466/a04678c2/source/xamarin-macios/src/UIKit/UIApplication.cs:63,4	C#
>	0x8 in iOSNullRef.iOS.Application.Main at C:\Xamarin\iOSNullRef\iOSNullRef\iOSNullRef.iOS\Main.cs:17,4	C#

Does not happen with HasUnevenRows=false

Steps to Reproduce:
Press Toggle Button twice in attached simple example.

Actual Results: 
The application crashes.

Expected Results: 
The ListView should show the new content.

Build Date & Hardware: 
Occurs on Forms and pre1 with iOS Simulator iOS 10.3
Does not occur on Android or UWP. 
Does not occur on Forms 2.3.4
Comment 1 Jimmy [MSFT] 2017-04-28 22:18:38 UTC
I am able to reproduce this issue using the attached project and repro steps. I can confirm that this is a regression in 2.3.5.

As mentioned, the crash does _not_ occur if HasUnevenRows = false.

Complete stacktrace: https://gist.github.com/jimmgarrido/ff552aef31497910099e78746792c0db

### Regression test
2.3.5-pre2  BAD   GOOD   GOOD
Comment 2 Samantha Houts [MSFT] 2017-05-02 19:54:12 UTC
Comment 3 Samantha Houts [MSFT] 2017-05-10 18:05:14 UTC
Should be fixed in 2.3.5-pre3. Thank you!
Comment 4 Saurabh Paunikar 2017-06-29 12:00:38 UTC
Fixed verified on 
Xamarin.Forms version

Microsoft Visual Studio Enterprise 2015
Version 14.0.25431.01 Update 3
Microsoft .NET Framework
Version 4.6.01586

Installed Version: Enterprise

Xamarin (de55d19)
Xamarin.Android (f6289cd)
Xamarin.iOS (494fcbc)