I have an app that appears to run without problems in normal use. The Clang Static Analyzer reports no problems either. When I try to run it in Instruments, it fails with an unrecognized selector exception.
The offending line is a simple property setter of the form:
self.bar = baz;
To figure out what's going on, I added an NSLog() call immediately above it:
NSLog(#"class = %# responds = %d", [self class], [self respondsToSelector:#selector(setBar:)]);
self.bar = baz;
On the emulator (without Instruments) and on a device, this shows exactly what I'd expect:
class = Foo responds = 1
When running under Instruments, I get:
class = Foo responds = 0
I'm stumped as to what could cause this. Perhaps a different memory location is getting tromped on when it's in the Instruments environment? Can anyone suggest how I might debug this?
If bar belongs to self, can't you do bar=baz; ?
Check your properties.
Perhaps to you need a cast on baz?
There's not enough information here to know what's going on, but then, if you knew what information to provide you'd probably have already fixed it. So. A few things to check:
Is the "self" pointer being swizzled in any way? Try printing out the value of self at various points just for sanity's sake
When your code runs in Instruments, is it running in a different mode? (32-bit vs. 64-bit, Garbage collected vs. Retain-Release, etc.) I'm not sure why any of those would have an effect, but if it's running in a different mode, that's something to look into.
Are you synthesizing the setter correctly? Or is it being provided dynamically (via Core Data, etc.)? If you manually specify a setBar: method, do you still get the error?
Related
I have problem with Thread 1: EXC_BAD_ACCESS (code=1, address=0xf00000c) and I don't know how to resolve it.
It appeared when I change some object in core date and save it and I try to pop this controller to parent.
This error is in main() with retVal.
here is some code
int retVal;
#try {
retVal = UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
*/\ error is here**
}
#catch (NSException *exception) {
NSLog(#"%#", [exception callStackSymbols]);
#throw exception;
}
return retVal;
After re-runing app all my changes are in core data. What is more this problem is only on iOS 7. iOS 6.1 is ok.
Does someone have idea how to resolve it?
As a comment said this error is likely to be deep in your code. If the culprit is a zombie, the easiest way to find it is to run it (preferably in the latest Xcode, currently Xcode 5, as it has been improved) in profiler and choose "Zombies". When it fails, you can see the history of everything that has happened to the object.
Also, set an exception breakpoint. You may get a break when the error happens instead of in main, where the exception gets passed up.
I just had the exact same problem.
Looked here and found nothing so I started backtracking until I thought, maybe I should try Clean Build Folderš¤
I was glad it was as easy as CLEAN BUILD FOLDER!!!
Product- Clean Build Folder(ā§ ā K)
š
I resolved this problem with "Zombies" and the problem was with
[UIScrollView(UIScrollViewInternal) _notifyDidScroll]
I added
- (void)dealloc {
self.tableView.delegate = nil;
}
This problem was only in iOS 7.
Thanks for help!
I have resolve this issue only by debugging the source code and re-analyze my logic.
Below are some reference that help me lot.
EXC_BAD_ACCESS means that message was sent to a point in the memory where thereās no instance of a class to execute it. Thus ābad accessā.
You will get EXC_BAD_ACCESS in 3 cases:
An object is not initialized
An object is already released
Something else that is not very likely to happen
Thatās already a good starting point. Start using the debugger, if you recently added a new object to the class youāre working on, put a breakpoint at the line before the freshly added object is used for the first time and check the values in the debugger.
Whatās happening most though is that you will be sending a message to an overreleased object ā i.e. object that is gone from the call stack. In this cases everything (and indeed everything) you will get in the console will be just :EXC_BAD_ACCESS
This is because the object is gone, there is no information what class was it, or what source file or anything else.
Please try to avoid using zombies for this.
EXC_BAD_ACCESS means there is no instance of a class to execute it.
There are 2 or more possibilities:
An object is not initialized
An object is already released
Please debug application carefully and analyze each object carefully. That might solve your issue.
I solved the same problem by finding out that the name of one of my NSString variables had the same name as one of the frameworks' class variables. Took seconds to change the name a little and problem disappeared.
With such a huge number of class variables in frameworks, it is very likely that once in a while, every programmer just by coincidence names some variable in his class exactly the same as one used somewhere in framework classes.
So it doesn't have to be Xcode bug in most cases.
In my case, I was using third-party library and I forgot to set custom-class name in Storyboard Identity Inspector
And there may be another issue which I faced today:
I had a mutable dictionary with a non-object entry try. There was a code snippet with adding a BOOL value to the dictionary. So no wonder that I got this error =).
In my case it was trying to log an Int32 with %s in print statement
in my view this is the equivalent of every other language NullPointerException,
but unlike other languages there are no hellping pointers (class name / method or line of the occurrence / god forbid a Stacktrace),
so the only thing i could do to solve it fast is to start printing main functions and views, (a very primitive solution),
create a swift: Debug.swift
add this function into Debug.swift:
public func trace(_ message: String = "", file: String = #file, function: String = #function, line: Int = #line)
{
print("**** \(file).\(function)[\(line)]: \(message)")
}
then you can use it like this:
trace("initializing")
to use it inside a var do this:
let _ = trace("initializing")
this should print something similar to this:
**** /path/to/my/file/MyFile.swift.someFunc()[18]: initializing
this is how i started adding debug lines to gain some flow record, so next time i have a EXC_BAD_ACCESS i will have a clue where the problem leis
don't forget to disable the prints during production deployment
I want to test my app's crash reporting out in the field by deliberately having it crash when the user performs a particular action that a real user is unlikely to do accidentally.
But what's a good reliable way of making the app crash that doesn't create a warning at compile time?
Edit: Note that many seemingly obvious answers to this question result in exceptions that get caught by Cocoa and thus don't result in the app crashing.
in Objective-C use C directly to cause a bad access
strcpy(0, "bla");
Note: while this works on any system I know -- in a future version of the C runtime OR the compiler this might not lead to a crash anymore. see Is null pointer dereference undefined behavior in Objective-C?)
(in swift you would have to bridge to objC to do this)
My current favourite:
assert(! "crashing on purpose to test <insert your reason here>");
A classic:
kill( getpid(), SIGABRT );
And some pr0n:
*(long*)0 = 0xB16B00B5;
All of them generate crashes captured by my crash reporting tool.
Since we all use Clang for iOS, this is fairly reliable:
__builtin_trap();
This has the benefit that it's designed for exactly this purpose, so it shouldn't generate any compiler warnings or errors.
How about a good old stack overflow :)
- (void)stackOverflow
{
[self stackOverflow];
}
abort(); causes abnormal terminationā¦ That is a crash.
Most popular one - unrecognised selector crash:
NSObject *object = [[NSObject alloc] init];
[object performSelector:#selector(asfd)];
Make sure you don't have -asdf method implemented in that class haha
Or index beyond bound exception:
NSArray * array = [NSArray array];
[array objectAtIndex:5];
And of course
kill( getpid(), SIGABRT );
I think in Swift you could easily throw a fatal error:
func foo() {
fatalError("crash!")
}
It is actually even intended to use this feature in case something goes wrong in order to make the app crash.
To avoid an if statement in a special case, you could use precondition, too. It's similar to assert, makes thus the intention (if wanted) pretty clear and is not removed in the final release as assert. It is used like precondition(myBoolean, "This is a helpful error message for debugging.").
Send a message to a deallocated object
exit(0);
(must... type... 30 characters)
You can also raise an exception:
[NSException raise:NSInternalInconsistencyException
format:#"I want to test app crashes!."];
Add a gesture recognizer to a view that recognizes a 10 finger tap (5 fingers for iPhone as 10 can get a bit crowded). The GR has a method attached to it that executes anyone of the previously mentioned surefire ways to get your app to crash. Most users are not going to lay 10 fingers down on your app, so you're safe from the general user accidentally causing the crash.
However you should be able to use something like Testflight or just deploying it to personal devices and test in the wild before ever submitting it to Apple. Having a forced crash could get your app rejected by Apple.
could try something like
NSArray* crashingArray = [NSArray arrayWithCapacity:1];
[crashingArray release];
should crash on an EXC_BAD_ACCESS (might need to release it a second time but normaly it should crash like this already)
I will go with:int raise(int sig);
To get more info >man raise
I would just kill the process normally:
kill(getpid(), SIGKILL);
So if you install a handler with signal you can also handle the crash, finishing to write opened files and these things.
I use
[self doesNotRecognizeSelector:_cmd];
When working with RubyMotion I use this:
n=Pointer.new ('c', 1)
n[1000] ='h'
Try this:
- (IBAction)Button:(id)sender
{
NSArray *array = [NSArray new];
NSLog(#"%#",[array objectAtIndex:8]);
}
a wrong NSLog statement will do it
NSLog(#"%#",1);
I have a NSManagedObject which I'm trying to instantiate with given values. I access the setters like so:
object.couchID = (NSString *)[dictObject objectForKey:#"_id"];
...and this works fine on my machine, but my partner gets this error when he runs it on his machine:
'-[NSCFString type]: unrecognized selector sent to instance 0x4e465e0'
About 90% of the setters (all formatted in the same way) work on my partner's machine, but a good 10% fail with that error. All of them work on my machine.
We're running the exact same code (according to SVN (yes, I know)), and fetching the same data from the same server, so everything seems like it should work.
We've checked the objects being passed, and they're the same. Commenting out the setter allows the code to get through to the next troublesome setter, but of course we need it to actually work. How else should we troubleshoot? Thanks in advance.
Update 1: Unlocked the Tumbleweed badge for that one... guess it's too sticky to touch? Any thoughts or guesses are welcome. And hey, you could earn 50 points.*
Update 2: the mixed-good-news is that checking out a fresh version from source control results in the same problem on my machine, so a) it's definitely something in the code, and b) I can more actively troubleshoot. Thanks for all your suggestions so far, I'm going to go through them all again.
I ran into something similar at work the other day. I suspect that one of you has a stale .momd file inside the app bundle, and that it's not being replaced when it gets upgraded. I suspect this is a bug in Xcode 4, though I haven't totally verified it yet. If your partner deletes the app completely and then installs the app, does the error go away?
You may need to create a temporary variable whose value is object cast to whatever the actual class is, e.g.
MyClass *c = (MyClass *)object; // if object is in fact a MyClass instance
c.couchID = (NSString *)[dictObject objectForKey:#"_id"];
I have seen cases where the compiler cannot make mental leap and realize that your attribute is the class you know it is. The solution for me in these cases has been to be more explicit. Does this make sense? It's worth a shot at least, no? :-)
if this code fails on your partner's machine:
someManagedObject.couchID = #"some hardcoded string";
seems like you have a dangling pointer: i would check that someManagedObject is properly retained and still a valid object when you try to call the -setCouchID method on it.
I have had nearly the same problem when trying to draw a CATiledLayer with data in NSManagedObjects. What should be a valid object barfs with an "unrecognised selector" exception
It nearly always happens because theres no retain on the object external to the point where you are trying to set or get the property. Being in a separate thread seemed to have a relationship too.
After fruitlessly trying to get round this with [NSManagedObjectContext lock] and retain on the context within the new thread I eventually just threw the contents of my fetch into a mutable set to try and keep a grip on it which seems to work on iOS but not on OS X so well.
So a couple of possibilities
Are you doing this not in the main
thread and does the MOC have a retain
within that thread. Check the docs
for [NSManagedObjectContext lock]. But essentially each thread working with the context needs its own retain on the context.
Try throwing it into a container
while you operate on it. Make it a
bit stickier. Sorry if that sounds
like voodoo but it is.
I'm working on an existing, large-ish codebase, and after upgrading the iOS SDK to 4.1 I am now seeing very strange behaviour. The crux of the matter appears to be a particular class that will no longer alloc - it is throwing a bad access in obj_msgSend, and seems to be the Class object on the stack that objc_msgSend doesn't like - although it is not actually NULL.
The original failing line looked like this:-
tileProjection = [[RMFractalTileProjection alloc] initFromProjection:proj tileSideLength:sideLength maxZoom:18];
I deconstructed this to isolate the problem:-
RMFractalTileProjection *p = [RMFractalTileProjection alloc]; // <- this crashes
p = [p initFromProjection:proj tileSideLength:sideLength maxZoom:18];
tileProjection = p;
I then tried this:-
Class c = NSClassFromString(#"RMFractalTileProjection");
assert(c);
NSLog( #"RMFractalTileProjection class(ptr) %p", c ); // <- prints an address OK
NSLog( #"RMFractalTileProjection class(obj) %#", c ); // <- crashes
In the debugger it looks like the Class object is sensible, but NSLog crashes when it tries to print it.
One thing to note: the class in question is declared as below, and I'm not sure if the protocol is causing a problem. Because this particular part is a large chunk of open source code, it is very difficult to remove this protocol requirement to see if that makes a difference.
#interface RMFractalTileProjection : NSObject<RMMercatorToTileProjection>
{
...
}
Any help on this one greatly appreciated - it is a show stopper.
Thanks
This is not really an answer but some ideas to move forward.
The only causes that leap to mind at the moment are memory corruption and some sort of link issue. Perhaps you are linking two versions of the class somehow.
Assuming this is the class, there doesn't look to be anything wrong to make it crash in alloc. There's no +initialize or anything.
Questions I would be asking myself and trying to answer are:
what happens if I rename the class?
what happens if I create a new identical class with a different name?
the pointer that gets passed to obj_msgSend: is it reasonable? does it point to something that looks like a class?
do you ever subclass the class and do you use initialize on the subclass?
is the pointer always the same? If so you can watch what it points to and see if it changes during execution.
what happens if you send self to the class?
OK, finally found this. As Jeremy suggested, this turned out to be a regular memory stomper.
The difficulty I had finding it was that it wasn't the Class object itself that was getting stomped, but the class' metaclass structure - which is a normal Class object but one level up, referenced by the class 'isa' pointer. That's why the class looked OK to me when I inspected it in the debugger - I need to follow the isa pointer and dump memory at one level up to find this. Luckily for me, the class was only a subclass of NSObject - had it been deeply subclassed, this could have been much harder to find. I got my first clue after biting the bullet, reverse-engineering objc_msgSend, working out exactly what was on the stack frame, and following all the pointers. Yep, the hard way :)
Matt Gallaghar's post (and various others I found by following links) were invaluable in helping me through this maze - thanks guys!
Burned a lot of time on this one, but on the up side I learned a hell of a lot about Objective C internals during the past day and a half :)
Thanks for these suggestions JeremyP - it is always good to have fresh suggestions after you've been banging your head against the keyboard all day!
Your suggestion of creating an identical class with the same name appears to have fixed the problem. I have no idea why and I feel I need to understand what's going on here. You're right it sounds like some kind of linker issue, but I still have no idea what could cause such a serious runtime error and not even produce a warning at build time.
Re. the pointer, it does look reasonable, but something inside the class eventually gets dereferenced as a null pointer inside objc_msgSend. Occasionally, after I have changed the code and rebuilt, I get a null pointer instead. This behaviour obviously suggests something nondeterministic like a memory stomp.
I'll post my findings.
I appear to have some overzealous releasing going on in my obj-C app - getting error message
"-[myobj release]: message sent to deallocated instance 0x5633b0"
. I know the class of the object instance causing the problem, but this class is used all over to create many instances.
My thought is I could put some logging in the init method of the class to log whatever "0x5633b0" corresponds to which should help me track down where the instance is being created.
What exactly is the "0x5633b0" and is there any way I can get access to that value in the code to log it?
Thanks.
What worked best for me when I ran into similar problems recently was the following:
Under under Project->Edit Active Executable -> Arguments tab -> Environment variables section I added and set to YES the following variables: NSAutoreleaseFreedObjectCheckEnabled, NSZombieEnabled and NSDebugEnabled.
Under the Run menu, I selected Enable Guard Malloc.
With these settings the debugger provided more hints on what's wrong with my code.
(I found these tips here)
Good luck,
Ori
0x5633b0 is likely the address of object in question (the value of self). You can use NSLog or printf with %p to print it.
0x5633b0 is likely the address of the deallocated object (the value of myobj). You can use NSLog or printf with %p to print it.
You can also use the instruments profiler to find the deallocated object.
1. Start the profiler:
2. Select the "Zombies" and start the profiler.
3. Click through the simulator until you hit your "deallocated error case"
In the debugger, type info symbol 0x5633b0 and you'll get some indication as to what object it is. One other thing that might be helpful is backtrace which will give you a stack trace. All in all, this blog entry has some great tips.
you can also add these to environment variables:
MallocStackLoggingNoCompact 1
and write in the gdb console:
info malloc-history <paste-address-here>
Reference: here
Consider using the NSZombieEnabled flag.
You will then know what is this deallocated object you're sending a message.
You're not managing your memory properly -- you're calling release/autorelease on some object more times than you're calling retain. Make sure you're following all of the rules laid out in the Memory Management Programming Guide for Cocoa.
0x5633b0 is just the address of the memory location at which the object is stored. One thing you can try to do is to add some code to the init method:
- (void) init
{
if(self == (MyClass*)0x5633b0)
NSLog(#"Allocated object at address 0x5633b0"); // put a breakpoint on this line
// do rest of init...
}
If you have any other init methods (e.g. initWithCoder:, which is called for objects instantiated from a XIB), make sure to put this snippet in those methods as well. Put a breakpoint on the NSLog line, and then see when it gets hit. Note that it may get hit several times, if an object is allocated at that address, deallocated, and then another object happens to be reallocated at the same address. The last hit before the crash is the one you want.