[iOS] Fix for NullReferenceException in WillMoveToParentViewController When Removing Page During Navigation#27275
Merged
jfversluis merged 6 commits intodotnet:mainfrom Jan 25, 2025
Conversation
Contributor
|
Hey there @praveenkumarkarunanithi! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed. |
vishnumenon2684
added
the
partner/syncfusion
Contributor
|
/azp run |
This comment was marked as outdated.
This comment was marked as outdated.
|
Azure Pipelines successfully started running 3 pipeline(s). |
Contributor
|
/azp run |
|
Azure Pipelines successfully started running 3 pipeline(s). |
jfversluis
approved these changes
Jan 25, 2025
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to subscribe to this conversation on GitHub.
Already have an account?
Sign in.
4 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Root Cause
The
NullReferenceExceptionoccurs when a non-current page is removed from the navigation stack. Specifically, when RemovePage is invoked for a page that is not the current one, theNavigationPage.Legacy.RemovePagemethod synchronously calls_removePageRequested?.Invoke(this, new NavigationRequestedEventArgs(page, true)). This invocation triggers theRemovePagemethod in the NavigationRenderer, which immediately callsDispose(). TheDispose()method then callsDisconnect(), setting the Tracker to null before the nativeWillMoveToParentViewControllermethod is executed. As a result, whenWillMoveToParentViewControllerattempts to access the now null Tracker, a NullReferenceException is thrown.In contrast, removing the current page using
PopAsynchandles the removal asynchronously. This ensures thatWillMoveToParentViewControlleris called while the Tracker remains valid. Only after the native operations complete does Disconnect(false) nullify the Tracker. This proper sequencing maintains the integrity of the Tracker during native method execution, preventing the exception when usingPopAsync.Description of Change
The fix adds a null check for
ToolbarTrackerin theWillMoveToParentViewControllermethod, ensuring it is accessed only when initialized, thereby preventing theNullReferenceException.Issues Fixed
Fixes #25726
Tested the behaviour in the following platforms
Screenshots
BeforeFix.mov
AfterFix.mov