NSMutableString appendString generates SIGABRT Error

Question

New here (this forum and Xcode in general), so bear with me.

I've spent multiple hours off and on over the last severals days trying to track down what exactly that I'm doing wrong here, but I just don't seem to be able to pinpoint my issue.

Here's the relevant sections of my code (I believe).

In the header:

@interface BlahViewController : UIViewController {

  NSMutableString *display;

}

@property (nonatomic, retain) NSMutableString *display;

In the main:

@implementation BlahViewController

@synthesize display;

- (void)viewDidLoad {
    self.display = [[NSMutableString alloc] init];  
}

- (void)anotherFunction:(UIButton *)sender {

    NSString *info = [[sender titleLabel] text];

    [self.display appendString:info];
}

I run the code, press the UIButton, and I get an error. Here's the initial throw:

  *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM appendString:]: unrecognized selector sent to instance 0x4e3d300' ***

Thanks!

EDIT: The whole stack trace was requested, so here it is (after reviewing the stack I realize there may be confusion, I'm writing a very basic calculator currently, so the ViewController, etc, should consider that backdrop and "anotherFunction" = "digitPressed" in this particular case):

* Call stack at first throw: (

0 CoreFoundation 0x00e345a9 exceptionPreprocess + 185
1 libobjc.A.dylib 0x00f88313 objc_exception_throw + 44
2 CoreFoundation 0x00e360bb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
3 CoreFoundation 0x00da5966 __forwarding + 966
4 CoreFoundation 0x00da5522 _CF_forwarding_prep_0 + 50
5 Calculator 0x0000273b -[CalculatorViewController digitPressed:] + 113
6 UIKit 0x002bb4fd -[UIApplication sendAction:to:from:forEvent:] + 119
7 UIKit 0x0034b799 -[UIControl sendAction:to:forEvent:] + 67
8 UIKit 0x0034dc2b -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
9 UIKit 0x0034c7d8 -[UIControl touchesEnded:withEvent:] + 458
10 UIKit 0x002dfded -[UIWindow _sendTouchesForEvent:] + 567
11 UIKit 0x002c0c37 -[UIApplication sendEvent:] + 447
12 UIKit 0x002c5f2e _UIApplicationHandleEvent + 7576
13 GraphicsServices 0x01723992 PurpleEventCallback + 1550
14 CoreFoundation 0x00e15944 CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION + 52
15 CoreFoundation 0x00d75cf7 __CFRunLoopDoSource1 + 215
16 CoreFoundation 0x00d72f83 __CFRunLoopRun + 979
17 CoreFoundation 0x00d72840 CFRunLoopRunSpecific + 208
18 CoreFoundation 0x00d72761 CFRunLoopRunInMode + 97
19 GraphicsServices 0x017221c4 GSEventRunModal + 217
20 GraphicsServices 0x01722289 GSEventRun + 115
21 UIKit 0x002c9c93 UIApplicationMain + 1160
22 Calculator 0x00002254 main + 102
23 Calculator 0x000021e5 start + 53
)
terminate called after throwing an instance of 'NSException'
Current language: auto; currently objective-c

The 'self.display = [[NSMutableString alloc] init];' line is a memory leak. You should instead use self.display = [[[NSMutableString alloc] init] autorelease]; or self.display = [NSMutableString string]; — romrom
Is it a memory leak if I release it in my viewDidUnload method? Because the way it's arranged now is that the -viewDidLoad alloc/inits and the -viewDidUnload releases. — Meshach
'display' is a property with retain memory management. So when you do self.display = [[NSMutableString alloc] init]; it is strictly equivalent to [display release]; display = [[[NSMutableString alloc] init] retain]; and you have a retain count of 2. If you have self.display = nil in you viewDidUnload method, you're decreasing the retain count by one, so there is still some memory allocated for the string but no way to access it anymore. It's a leak. — romrom

bbum bbum · Accepted Answer · 2011-06-20T17:40:36

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM appendString:]: unrecognized selector sent to instance 0x4e3d300' *

This indicates that you are calling appendString: an instance of some kind of NSArray, which obviously won't work.

Assuming that [self.display appendString:info]; is the actual source of the exception, then it is happening because self.display has likely been over-released and, coincidentally, an NSArray instance was allocated at the same place in memory.

You could use zombie detection to debug this.

Alternatively, you might be corrupting memory somewhere. Or, maybe, there is another assignment to display.

In any case, whenever you have a crash, there will be a backtrace. Please post it. There is the off chance that the crash is happening somewhere else.

5 Calculator 0x0000273b -[CalculatorViewController digitPressed:] + 113

Show the source to your digitPressed: method.

self.display = [[NSMutableString alloc] init];

That is a memory leak; it'll be retained twice. Just do self.display = [NSMutableString string]; and self.display = nil; (in your viewDidUnload).

But that isn't the source of your problem; something is resetting the display variable or it is being over-released. Show all uses of display.

NSMutableString appendString generates SIGABRT Error

1 Answers