Bug 42755 - Crash due to Null Reference Exception in OpenGLViewRenderer
Summary: Crash due to Null Reference Exception in OpenGLViewRenderer
Alias: None
Product: Forms
Classification: Xamarin
Component: iOS ()
Version: 2.3.2
Hardware: All All
: --- normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2016-07-22 18:54 UTC by Stuart Fischer
Modified: 2017-05-23 18:07 UTC (History)
2 users (show)

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

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Description Stuart Fischer 2016-07-22 18:54:19 UTC
In testing my local fix for Bugzilla #41413, (change from using NSRunLoop.NSDefaultRunLoopMode to NSRunLoop.NSRunLoopCommonModes on OpenGLViewRenderer.cs line 101), I observed a crash in OpenGLViewRenderer.cs on line 96, when multiple OpenGLViewRenderers exist in the same app (eg. different Sub-views).

A View (the map in our app) instantiates a Xamarin.Forms OpenGLView (using OpenGLViewRenderer), then another View (a match-3 game on an overlaying view) instantiates a second OpenGLView. Around the time the 2nd view is instantiated, there is a Null Reference Exception on line 96 ("_displayLink.Invalidate()") of OpenGLViewRenderer.cs.

This can happen because the Dispose() method of OpenGLViewRenderer.cs is setting _displayLink to null (on line 45), but the run-loop may thereafter attempt to access the (nulled) _displayLink on line 96. If one adds a guard for null _displayLink to the condition of line 94, the problem no longer occurs:

BEFORE (line 94 of OpenGLViewRenderer.cs):

 if (control == null || model == null || !model.HasRenderLoop)

AFTER, with null guard (line 94):

 if ((control == null || model == null || !model.HasRenderLoop)&&(_displayLink!=null))

I think this adding this null guard on line 94 is one solution to this issue.
Comment 1 Rui Marinho 2017-05-23 18:07:49 UTC
Should be fixed on 2.3.6-pre1