Bug 54401 - Pages do not get garbage collected after popping them from the navigation stack
Summary: Pages do not get garbage collected after popping them from the navigation stack
Alias: None
Product: Forms
Classification: Xamarin
Component: Android ()
Version: 2.3.5
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2017-04-03 12:39 UTC by Josha Munnik
Modified: 2017-07-12 22:45 UTC (History)
4 users (show)

Tags: ac android memoryleak navigation
Is this bug a regression?: ---
Last known good build:

Test project using Debug.WriteLine within destructors. (188.42 KB, application/x-zip-compressed)
2017-04-03 12:39 UTC, Josha Munnik

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Description Josha Munnik 2017-04-03 12:39:14 UTC
Created attachment 21149 [details]
Test project using Debug.WriteLine within destructors.

The latest instance of a page that contains one or more ToolbarItem entries in the ToolbarItems property does not get garbage collected after popping it from the navigation stack.

It will get garbage collected once a new instance of the *same* page type is pushed on the navigation stack.

Pages without ToolbarItem entries that are popped from the navigation stack are not garbage collected until a new page of any type is pushed onto the NavigationStack.

Tested with Android.
Comment 1 Jimmy [MSFT] 2017-04-03 15:02:53 UTC
Thank you for filing this! I will try to confirm the issue using the attached project and I will update the report.
Comment 2 Josha Munnik 2017-04-07 08:51:08 UTC
I solved this by adding the following handler to NavigationPage.Popped

    private void HandlePopped(object aSender, NavigationEventArgs anEvent) {
      foreach (ToolbarItem item in anEvent.Page.ToolbarItems) {
        item.Parent = null;
        // not doing this will not garbage collect the attached view model

Pages and view models get garbage collected.
Comment 3 Josha Munnik 2017-04-07 08:53:14 UTC
Forgot to mention, above has been tested with Xamarin Forms v2.3.4.224
Comment 4 Jimmy [MSFT] 2017-06-05 17:31:31 UTC
I can confirm this issue using the attached repro project. On iOS, when a page is popped it is automatically destroyed. However this is not happening on Android. 

While you can manually force a garbage collection so the popped pages are destroyed, this presents some other issues as mentioned in the description:

1. If a Page has ToolbarItems, it will not be garbage collected unless there was another page instance of the _same_ type on the stack. This means that the previous instance of this Page does _not_ get collected while the older instances are.

2. If a Page does not have ToolbarItems, then the Page will be collected as long as it is not the previous one. 

### Version Tests   BAD
2.3.5-pre3  BAD   BAD