Demystifying iOS Application Crash Logs
This is a blog post by Soheil Moayedi Azarpour, an independent iOS developer. You can also find him on Google+. Have you ever had the following experience as an app developer? Before you submit your app, you perform a lot of testing to make sure your app runs flawlessly. It works fine on your device, […] By Soheil Azarpour.
Scenario 2: Button FUBAR
A user writes: “I can’t bookmark a rage master as my favorite. When I try to, the app crashes…”
Another user says, “Bookmarking doesn’t work… I go to detail info, tap on bookmark button and BOOM!”
The above complaints don’t say much, and there could be any number of causes for the issue they’ve identified. Take a look at the crash log:
Incident Identifier: 3AAA63CC-3088-41CC-84D9-82FE03F9F354
CrashReporter Key: 5a56599d836c4f867f6eec76afee451bf9ae5f31
Hardware Model: iPhone4,1
Process: Rage Masters [20090]
Path: /var/mobile/Applications/B2121A89-3D1F-4E61-BB18-5511E1DC150F/Rage Masters.app/Rage Masters
Identifier: Rage Masters
Version: ??? (???)
Code Type: ARM (Native)
Parent Process: launchd [1]
Date/Time: 2012-11-03 13:39:00.081 -0400
OS Version: iOS 6.0 (10A403)
Report Version: 104
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Crashed Thread: 0
Last Exception Backtrace:
0 CoreFoundation 0x36bff29e __exceptionPreprocess + 158
1 libobjc.A.dylib 0x34f0f97a objc_exception_throw + 26
2 CoreFoundation 0x36c02e02 -[NSObject(NSObject) doesNotRecognizeSelector:] + 166
3 CoreFoundation 0x36c0152c ___forwarding___ + 388
4 CoreFoundation 0x36b58f64 _CF_forwarding_prep_0 + 20
5 UIKit 0x37fbb0a8 -[UIApplication sendAction:to:from:forEvent:] + 68
6 UIKit 0x37fbb05a -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 26
7 UIKit 0x37fbb038 -[UIControl sendAction:to:forEvent:] + 40
8 UIKit 0x37fba8ee -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 498
9 UIKit 0x37fbade4 -[UIControl touchesEnded:withEvent:] + 484
10 UIKit 0x37ee35f4 -[UIWindow _sendTouchesForEvent:] + 520
11 UIKit 0x37ed0804 -[UIApplication sendEvent:] + 376
12 UIKit 0x37ed011e _UIApplicationHandleEvent + 6150
13 GraphicsServices 0x3708359e _PurpleEventCallback + 586
14 GraphicsServices 0x370831ce PurpleEventCallback + 30
15 CoreFoundation 0x36bd416e __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 30
16 CoreFoundation 0x36bd4112 __CFRunLoopDoSource1 + 134
17 CoreFoundation 0x36bd2f94 __CFRunLoopRun + 1380
18 CoreFoundation 0x36b45eb8 CFRunLoopRunSpecific + 352
19 CoreFoundation 0x36b45d44 CFRunLoopRunInMode + 100
20 GraphicsServices 0x370822e6 GSEventRunModal + 70
21 UIKit 0x37f242fc UIApplicationMain + 1116
22 Rage Masters 0x000ca004 main (main.m:16)
23 libdyld.dylib 0x3b630b1c start + 0
The exception code is a SIGABRT. Usually, a SIGABRT exception is raised when an object receives an unimplemented message. Or to put it in simpler terms, there’s a call for a nonexistent method on an object.
Usually this won’t happen, since if you call method “foo” on object “bar”, the compiler will throw an error if the method “foo” doesn’t exist. But when you indirectly call a method using a selector, the compiler might not be able to determine whether or not the method exists on the object.
Back to the crash log. It indicates that the crashed thread is 0. This means that you’re probably looking at a situation where a method was called on an object on the main thread, where the object did not implement the method.
If you continue reading the backtrace log, you see that the only call related to your code is frame 22, main.m:16. That doesn’t help much. :[
Keep going up the framework calls, and there it is:
2 CoreFoundation 0x36c02e02 -[NSObject(NSObject) doesNotRecognizeSelector:] + 166
That isn’t your code. But at least it confirms that there was a call to an unimplemented method on an object.
Go to RMDetailViewController.m, since that’s where the bookmark button is implemented. Find the code that bookmarks the rage master:
-(IBAction)bookmarkButtonPressed {
self.master.isBookmarked = !self.master.isBookmarked;
// Update shared bookmarks
if (self.master.isBookmarked)
[[RMBookmarks sharedBookmarks] bookmarkMaster:self.master];
else
[[RMBookmarks sharedBookmarks] unbookmarkMaster:self.master];
// Update UI
[self updateBookmarkImage];
}
That looks OK, so check the storyboard (XIB file) and make sure that the button is hooked up correctly.
There it is! In MainStoryboard.storyboard, the button refers to bookmarkButtonPressed: instead of bookmarkButtonPressed (note the final colon indicating that the method expects a parameter). To fix this, replace the signature of the method above with this:
-(IBAction)bookmarkButtonPressed:(id)sender {
// Remain unchanged...
}
Of course, you could also simply remove the incorrect connection in the XIB file and reconnect to the method, so that the method signature is correct in the XIB file. Either way works.
And that’s another crash fixed. You’re getting pretty good at this. :]
Scenario 3: Another Bug On the Table
Another user complains saying, “I can’t delete bookmarked masters from the bookmarks view…” And another email about the same issue reads, “If I try to delete a master in bookmarks, the app crashes…”
By now, you are used to these emails not being very helpful. To the crash logs!
Incident Identifier: 5B62D681-D8FE-41FE-8D52-AB7E6D6B2AC7
CrashReporter Key: 5a56599d836c4f867f6eec76afee451bf9ae5f31
Hardware Model: iPhone4,1
Process: Rage Masters [20088]
Path: /var/mobile/Applications/B2121A89-3D1F-4E61-BB18-5511E1DC150F/Rage Masters.app/Rage Masters
Identifier: Rage Masters
Version: ??? (???)
Code Type: ARM (Native)
Parent Process: launchd [1]
Date/Time: 2012-11-03 13:38:45.762 -0400
OS Version: iOS 6.0 (10A403)
Report Version: 104
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Crashed Thread: 0
Last Exception Backtrace:
0 CoreFoundation 0x36bff29e __exceptionPreprocess + 158
1 libobjc.A.dylib 0x34f0f97a objc_exception_throw + 26
2 CoreFoundation 0x36bff158 +[NSException raise:format:arguments:] + 96
3 Foundation 0x346812aa -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 86
4 UIKit 0x37f04b7e -[UITableView(_UITableViewPrivate) _endCellAnimationsWithContext:] + 7690
5 UIKit 0x3803a4a2 -[UITableView deleteRowsAtIndexPaths:withRowAnimation:] + 22
6 Rage Masters 0x000fd9ca -[RMBookmarksViewController tableView:commitEditingStyle:forRowAtIndexPath:] (RMBookmarksViewController.m:68)
7 UIKit 0x3809a5d4 -[UITableView(UITableViewInternal) animateDeletionOfRowWithCell:] + 80
8 UIKit 0x37fbb0a8 -[UIApplication sendAction:to:from:forEvent:] + 68
9 UIKit 0x37fbb05a -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 26
10 UIKit 0x37fbb038 -[UIControl sendAction:to:forEvent:] + 40
11 UIKit 0x37fba8ee -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 498
12 UIKit 0x37fbb0a8 -[UIApplication sendAction:to:from:forEvent:] + 68
13 UIKit 0x37fbb05a -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 26
14 UIKit 0x37fbb038 -[UIControl sendAction:to:forEvent:] + 40
15 UIKit 0x37fba8ee -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 498
16 UIKit 0x37fbade4 -[UIControl touchesEnded:withEvent:] + 484
17 UIKit 0x37ee35f4 -[UIWindow _sendTouchesForEvent:] + 520
18 UIKit 0x37ed0804 -[UIApplication sendEvent:] + 376
19 UIKit 0x37ed011e _UIApplicationHandleEvent + 6150
20 GraphicsServices 0x3708359e _PurpleEventCallback + 586
21 GraphicsServices 0x370831ce PurpleEventCallback + 30
22 CoreFoundation 0x36bd416e __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 30
23 CoreFoundation 0x36bd4112 __CFRunLoopDoSource1 + 134
24 CoreFoundation 0x36bd2f94 __CFRunLoopRun + 1380
25 CoreFoundation 0x36b45eb8 CFRunLoopRunSpecific + 352
26 CoreFoundation 0x36b45d44 CFRunLoopRunInMode + 100
27 GraphicsServices 0x370822e6 GSEventRunModal + 70
28 UIKit 0x37f242fc UIApplicationMain + 1116
29 Rage Masters 0x000fb004 main (main.m:16)
30 libdyld.dylib 0x3b630b1c start + 0
This looks very similar to the previous crash log. It’s another SIGABRT exception. Perhaps you wonder if it’s the same issue: sending a message to an object that has not implemented the method?
Let’s traverse through the backlog and see what methods were called. Start from the bottom. The last call to your code in Rage Masters is at frame 6:
6 Rage Masters 0x00088c66 -[RMBookmarksViewController tableView:commitEditingStyle:forRowAtIndexPath:] (RMBookmarksViewController.m:68)
Well, this is a UITableViewDataSource method. Huh?! You are pretty sure Apple has implemented this method – you can override it, but it is not like it hasn’t been implemented. Plus, it is an optional delegate method. So the problem isn’t a call to an unimplemented method.
Take a look at the frames after that call:
3 Foundation 0x346812aa -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 86
4 UIKit 0x37f04b7e -[UITableView(_UITableViewPrivate) _endCellAnimationsWithContext:] + 7690
5 UIKit 0x3803a4a2 -[UITableView deleteRowsAtIndexPaths:withRowAnimation:] + 22
In frame 5, UITableView is calling another method of its own, deleteRowsAtIndexPaths:withRowAnimation: and then _endCellAnimationsWithContext: is called, which looks like an internal Apple method. Then the Foundation framework raises an exception, handleFailureInMethod:object:file:lineNumber:description:.
Putting the above together with the user complaints, it looks as if you are dealing with a buggy deletion procedure in UITableView. Go to Xcode. Do you know where to go? Can you tell from the crash log? It’s line 68 in RMBookmarksViewController.m:
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
[self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
}
Can you tell where the problem is? I’ll wait while you take a look.
You got it! How about the data source? The code deletes a row in the table view, but doesn’t change the data source behind it. To fix this, replace the above method with the following one:
-(void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
RMMaster *masterToDelete = [bookmarks objectAtIndex:indexPath.row];
[bookmarks removeObject:masterToDelete];
[[RMBookmarks sharedBookmarks] unbookmarkMaster:masterToDelete];
[self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
}
That should do it! Take that, you nasty bug!! BIFF!!! BANG!!!! CRASH!!!!!