[MonoTouch] Any idea what could cause this crash?

Thu Mar 22 12:13:39 UTC 2012

Rolf,

while composing a reply with some code fragments, I realized that I was
missing an InvokeOnMainThread() while changing my UI.

Chances are high that this caused the problem. I’ll keep an eye on it.
Thanks for asking for the code! J

In the world of Windows Forms, an application throws if you try to execute
UI related code on anything but the main thread.

In iOS it often seems to work and randomly crashes with obscure unhandled
exceptions. Would it be possible for MT to throw immediately like Windows
Forms does?

René

Von: Rolf Bjarne Kvinge [mailto:rolf at xamarin.com] 
Gesendet: Donnerstag, 22. März 2012 10:56
An: René Ruppert
Cc: monotouch at lists.ximian.com
Betreff: Re: [MonoTouch] Any idea what could cause this crash?

Hi,

On Thu, Mar 22, 2012 at 9:35 AM, René Ruppert <rene.ruppert at googlemail.com>
wrote:

Hi,

>From one out of hundred taps on a UIButton, I get the following crash. There
is no managed crash.

Hitting the button starts a new thread and that thread updates the UI by
using InvokeOnMainThread(). I was able to verify that it never crashes if I
do not use a separate thread.
What line is the key line here? What is nil/null? As I can see table view
 cells showing up in the crash, I assume it has to do with those.

I posted this stacktrace on SO a while ago and Rolf answered that the key is
at (4) but I've been unable to fix the problem.
Giving code is hard because I don't know what part of is causing the
problem.
Can I assume that something was setting a background color (8) and then it
 crashed at (4)?

Then I would be able to limit it to places where the

background color gets changed by me.

Native stacktrace:

       0   BrainloopBrowser                    0x00094fbc
mono_handle_native_sigsegv + 284
       1   BrainloopBrowser                    0x0000be72
mono_sigsegv_signal_handler + 178
       2   libsystem_c.dylib                   0x9401859b _sigtramp + 43
       3   ???                                 0xffffffff 0x0 + 4294967295
       4   QuartzCore                          0x04176891 -[CALayer
actionForKey:] + 89
       5   QuartzCore                          0x0417982d
_ZL12actionForKeyP7CALayerPN2CA11TransactionEP8NSString + 82
       6   QuartzCore                          0x0417c9c3
_ZN2CA5Layer12begin_changeEPNS_11TransactionEjRP11objc_object + 131
       7   QuartzCore                          0x04182ac1
_ZN2CA5Layer6setterEj12_CAValueTypePKv + 141
       8   QuartzCore                          0x04172ca4 -[CALayer
setBackgroundColor:] + 62
       9   UIKit                               0x021e2992
-[UIView(Internal) _setBackgroundCGColor:withSystemColorName:] + 1516
       10  UIKit                               0x021dbca5
-[UIView(Hierarchy) _setBackgroundColor:] + 145
       11  UIKit                               0x021dda06
-[UIView(Rendering) setBackgroundColor:] + 40
       12  CoreFoundation                      0x0113b51d __invoking___ +
29
       13  CoreFoundation                      0x0113b437 -[NSInvocation
invoke] + 167
       14  UIKit                               0x025c53a5
TaggingAppearanceGeneralSetterIMP + 1137
       15  UIKit                               0x02388523 -[UITableViewCell
_updateSeparatorContent] + 478
       16  UIKit                               0x02390e53 -[UITableViewCell
layoutSubviews] + 2681
       17  UIKit                               0x021e3322
-[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 178
       18  CoreFoundation                      0x011d6e72 -[NSObject
performSelector:withObject:] + 66
       19  QuartzCore                          0x0417392d -[CALayer
layoutSublayers] + 266
       20  QuartzCore                          0x0417d827
_ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 231
       21  QuartzCore                          0x04103fa7
_ZN2CA7Context18commit_transactionEPNS_11TransactionE + 377
       22  QuartzCore                          0x04105ea6
_ZN2CA11Transaction6commitEv + 374
       23  QuartzCore                          0x041059d3
_ZN2CA11Transaction14release_threadEPv + 65
       24  libsystem_c.dylib                   0x94009e0c
_pthread_tsd_cleanup + 85
       25  libsystem_c.dylib                   0x93fc264c _pthread_exit +
146
       26  libsystem_c.dylib                   0x93fc29a0 pthread_exit + 33
       27  BrainloopBrowser                    0x0020434e thread_exit + 30
       28  BrainloopBrowser                    0x00203d03
thread_start_routine + 163
       29  BrainloopBrowser                    0x001aeb20 gc_start_thread +
80
       30  libsystem_c.dylib                   0x93fc0ed9 _pthread_start +
335
       31  libsystem_c.dylib                   0x93fc46de thread_start + 34

This isn't the main thread. This code shouldn't be executing on any thread
but the main one, but this isn't directly executed from your code, so it's
not obvious what's going on.

Can you post the code you execute on the new thread? It's hopefully
something suspicious there.

Rolf

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