Bug 52376 - NullReferenceException when change the MainPage if the old page contains a ListView
Summary: NullReferenceException when change the MainPage if the old page contains a Li...
Alias: None
Product: Forms
Classification: Xamarin
Component: iOS ()
Version: 2.3.3
Hardware: PC Windows
: Normal normal
Target Milestone: ---
Assignee: Paul DiPietro [MSFT]
Depends on:
Reported: 2017-02-08 08:44 UTC by Suat Korkmaz
Modified: 2017-06-21 13:57 UTC (History)
5 users (show)

Tags: ios
Is this bug a regression?: ---
Last known good build:

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Description Suat Korkmaz 2017-02-08 08:44:50 UTC
ContentPage is unable to dispose if a child is a ListView when unloading.

You have a MasterDetailPage as MainPage. Load a ContentPage as Detail. The ContentPage contains a ListView. When you set another page as Detail the old page is unable to dispose the ListView.

Steps to Reproduce:
1- Create a Portable project.
2- Add a MasterDetailPage to the page you will load as Main page.
3- Create a ContentPage and put a ListView and a button in it.
4- Do not use any platform specific renderer on the ListView
5- Fill the ListView
6- In the clicked handler of the button set a new empty page to the app:
App.Current.MainPage = new ContentPage();

7- Set the ContentPage as Detail that you created in step #3
8- Run the app (ListView fills)
9- Click the button.

Actual Result: 
You should get a System.NullReferenceException

Expected Result:
You shouldn't get a System.NullReferenceException

Additional Information:
As a workaround I created a ListViewRenderer for iOS like:

public class CustomListViewRenderer : ListViewRenderer
        protected override void OnElementChanged(ElementChangedEventArgs<ListView> e)
        protected override void Dispose(bool disposing)

When I comment out the //base.Dispose(disposing); line then the app works.

PS: I'm sorry that I am unable to create a sample app right now.
Comment 1 Paul DiPietro [MSFT] 2017-03-27 03:42:34 UTC
I am not able to reproduce this but would like to get more info. Can you please verify the Forms version, iOS version, and device or simulator, and possibly upload a reproduction? I've put the ContentPage as the Detail with the ListView and button, and clicking the button sets App.Current.MainPage to a new ContentPage. Clicking that does not appear to cause a crash on my simulator running 10.2.
Comment 2 Rui Marinho 2017-06-21 13:57:50 UTC
Because we have not received a reply to our request for more information we are closing this issue. If you are still encountering this issue, please reopen the ticket with the requested information. Thanks!