Bug 25223 - IOS: MasterDetailPage does not dispose child renderers correctly
Summary: IOS: MasterDetailPage does not dispose child renderers correctly
Alias: None
Product: Forms
Classification: Xamarin
Component: Forms ()
Version: 1.3.0
Hardware: Macintosh Mac OS
: Normal normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2014-12-10 07:20 UTC by azinner
Modified: 2015-01-14 05:42 UTC (History)
5 users (show)

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

Sample solution (3.45 MB, application/zip)
2014-12-22 07:01 UTC, azinner

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Description azinner 2014-12-10 07:20:38 UTC
Although this is listed as a resolve bug in the 'Bug fixes' section of the prerelease 2,
when a (detail) page, that contains a map, is disposed during the assignment of a new detailPage, the app crashes on IOS.

Example code:

using System;
using Xamarin.Forms;
using Xamarin.Forms.Maps;

namespace MasterDetail
   public class App : Application
      MasterDetailPage _masterDetailPage = null;

      public App ()
         _masterDetailPage = new MasterDetailPage {

            Master = new ContentPage {
               Title = "Master",
               Content = new Button { 
                  Text = "Click to crash",
                  Command = new Command (o =>
                     // When this new detail page is assigned,
                     // the disposing of the previous seletced detail page with the map crashes ....
                     _masterDetailPage.Detail = new NavigationPage (new ContentPage{ });

            Detail = new NavigationPage (
               new ContentPage { 
                  Content = new Map () 

         MainPage = _masterDetailPage;

Stack trace:

System.NullReferenceException: Object reference not set to an instance of an object
at Xamarin.Forms.Maps.iOS.MapRenderer.Dispose (Boolean disposing) [0x00000] in <filename unknown>:0
at MonoTouch.Foundation.NSObject.Dispose () [0x00000] in /Developer/MonoTouch/Source/maccore/src/Foundation/NSObject2.cs:127
at Xamarin.Forms.Platform.iOS.Platform.DisposeModelAndChildrenRenderers (Xamarin.Forms.Element view) [0x00000] in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.Platform.HandleChildRemoved (System.Object sender, Xamarin.Forms.ElementEventArgs e) [0x00000] in <filename unknown>:0
at Xamarin.Forms.Element.OnDescendantRemoved (Xamarin.Forms.Element child) [0x00000] in <filename unknown>:0
at Xamarin.Forms.Element.OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in <filename unknown>:0
at Xamarin.Forms.Page.OnInternalRemoved (Xamarin.Forms.VisualElement view) [0x00000] in <filename unknown>:0
at Xamarin.Forms.Page.InternalChildrenOnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00000] in <filename unknown>:0
at System.Collections.ObjectModel.ObservableCollection`1[Xamarin.Forms.Element].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00014] in ///Library/Frameworks/Xamarin.iOS.framework/Versions/
at System.Collections.ObjectModel.ObservableCollection`1[Xamarin.Forms.Element].RemoveItem (Int32 index) [0x0001a] in ///Library/Frameworks/Xamarin.iOS.framework/Versions/
at System.Collections.ObjectModel.Collection`1[Xamarin.Forms.Element].Remove (Xamarin.Forms.Element item) [0x00011] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.Collections.ObjectModel/Collection.cs:134
at Xamarin.Forms.MasterDetailPage.set_Detail (Xamarin.Forms.Page value) [0x00000] in <filename unknown>:0
at MasterDetail.App.<App>m__0 (System.Object o) [0x00011] in /Users/Andre/Projekte/mobile/MasterDetail/MasterDetail/App.cs:23
at Xamarin.Forms.Command.Execute (System.Object parameter) [0x00000] in <filename unknown>:0
at Xamarin.Forms.Button.Xamarin.Forms.IButtonController.SendClicked () [0x00000] in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.ButtonRenderer.OnButtonTouchUpInside (System.Object sender, System.EventArgs eventArgs) [0x00000] in <filename unknown>:0
at MonoTouch.UIKit.UIControlEventProxy.Activated () [0x00007] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIControl.cs:33
at at (wrapper managed-to-native) MonoTouch.UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
at MonoTouch.UIKit.UIApplication.Main (System.String[] args, IntPtr principal, IntPtr delegate) [0x00005] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:62
at MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x00038] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:46
at MasterDetail.iOS.Application.Main (System.String[] args) [0x00008] in /Users/Andre/Projekte/mobile/MasterDetail/iOS/Main.cs:17

Work around: in OnDisappearing() of the page that contains the map I manually set "Content = null;".
But this may cause memory leaks ...
Comment 1 Lynn Koehler 2014-12-18 15:20:46 UTC
I'm running pre-3 of Forms and Maps and have this same problem - but only when the new detail page is replacing a page with a map in the Content.
Comment 2 Parmendra Kumar 2014-12-22 03:43:35 UTC
I have tried to reproduce this issue but I am not able to reproduce this.Please check the screencast and let me know if I have missed anything. Could you please provide us sample project, steps and environment info.? That can be helpful to reproduce at my end.

Screencast: http://www.screencast.com/t/H2uhhIDbr00
Comment 3 azinner 2014-12-22 07:01:16 UTC
Created attachment 9162 [details]
Sample solution

I can reproduce with the latest stable or beta channels:

XS 5.5.4
Comment 4 Parmendra Kumar 2014-12-22 07:30:20 UTC
I have checked this issue with attached sample in comment 3. I am getting same behavior mentioned in the bug description. 

Screencast: http://www.screencast.com/t/LbXlUlFA

ApplicationOutput: https://gist.github.com/Arpit360/a36a50986283282c5e42
BuildLog: https://gist.github.com/Arpit360/761308699661974c07a0
IdeLog: https://gist.github.com/Arpit360/f750e835f6443ced97cd

Environment info:

=== Xamarin Studio ===

Version 5.5.4 (build 15)
Installation UUID: 3d25a767-a003-4a7d-9f5e-e57987cf6cf0
	Mono 3.10.0 ((detached/92c4884)
	GTK+ 2.24.23 (Raleigh theme)

	Package version: 310000031

=== Apple Developer Tools ===

Xcode 6.1 (6602)
Build 6A1052c

=== Xamarin.Mac ===

Version: (Enterprise Edition)

=== Xamarin.Android ===

Version: (Enterprise Edition)
Android SDK: /Users/mac360_xamarin/Library/Developer/Xamarin/android-sdk-macosx
	Supported Android versions:
		2.1   (API level 7)
		2.2   (API level 8)
		2.3   (API level 10)
		3.1   (API level 12)
		4.0.3 (API level 15)
		4.4   (API level 19)
		5.0   (API level 21)
Java SDK: /usr
java version "1.7.0_71"
Java(TM) SE Runtime Environment (build 1.7.0_71-b14)
Java HotSpot(TM) 64-Bit Server VM (build 24.71-b01, mixed mode)

=== Xamarin.iOS ===

Version: (Enterprise Edition)
Hash: 7244769
Build date: 2014-12-11 14:54:30-0500

=== Build Information ===

Release ID: 505040015
Git revision: f93940a35458a18052f1a25e106e62ca970d9c40
Build date: 2014-11-19 15:32:41-05
Xamarin addins: dc23cbd91a3a0e1d326328e1229e86c942a49ec8

=== Operating System ===

Mac OS X 10.10.0
Darwin mac360-xamarins-Mac-mini.local 14.0.0 Darwin Kernel Version 14.0.0
    Fri Sep 19 00:26:44 PDT 2014
    root:xnu-2782.1.97~2/RELEASE_X86_64 x86_64
Comment 5 Jason Smith [MSFT] 2015-01-13 20:57:19 UTC
This no longer crashes in 1.3.1
Comment 6 Parmendra Kumar 2015-01-14 05:19:13 UTC
I have checked this issue with Xamarin.Forms 1.3.1 and now application don't crash.


Hence Closing this issue. Please reopen this issue if you getting same issue.

Environment info:

Xamarin Studio  5.7 (build 661)
Mono 3.12.0 ((detached/1538a59)
Xcode 6.1 (6602)
 Xamarin.iOS: (Enterprise Edition)
Xamarin.Mac: (Enterprise Edition)
Mac OS X 10.9.4
Comment 7 Parmendra Kumar 2015-01-14 05:42:21 UTC
Screencast: http://www.screencast.com/t/mzTAaayhl