I have a strange problem (strange if you ask me). Im using a NSNumber object to store a number (doh). When I try to "modify" it it crashes my application. The code I'm using looks like this:
if ([frequency intValue] > 19999)
return;
frequency = [NSNumber numberWithInt:([frequency intValue] + 1)]; //I think this line is causing me the problem
[freqLabel setText:[NSString stringWithFormat:#"%i Hz", [frequency intValue]]];
Where is frequency the NSNumber and freqLabel my label to which I write the value every time this gets called.
Why is this incorrect? It works when I call it for the first time. Is it that NSNumber numberWithInt always returns a new object which I'm trying to assign to frequency?
How do I fix this? Whats the correct way to change a NSNumber's value?
Sorry for my bad english (if there are any mistakes).
EDIT:
The error log looks like this:
[__NSCFType intValue]: unrecognized selector sent to instance 0x73430e0
2012-05-09 16:39:28.064 MyApp[31939:10703] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFType intValue]: unrecognized selector sent to instance 0x73430e0'
*** First throw call stack:
(0x17a6022 0x28afcd6 0x17a7cbd 0x170ced0 0x170ccb2 0x4821 0x17a7e99 0x49d14e 0x49d0e6 0x543ade 0x543fa7 0x543266 0x4c23c0 0x4c25e6 0x4a8dc4 0x49c634 0x2e49ef5 0x177a195 0x16deff2 0x16dd8da 0x16dcd84 0x16dcc9b 0x2e487d8 0x2e4888a 0x49a626 0x1cca 0x1c15)
terminate called throwing an exception
But it doesn't always show this error. Sometimes it causes an EXC_BAD_ACCESS. Should I store my variable in a temporary NSNumber?
You can't just alloc/init something once and then you have a lifelong reference to that type. When you assign frequency to numberWithInt, then you are overwriting the previous alloc/init value with an autorelease value (which will be released later and cause the exact behavior you are describing). The reason it works with self.frequency is because your property is set as a retain property, so it automatically retains the autorelease value. Add a retain to your numberWithInt line and it will be fine (or do what you are doing now with self.frequency).
I would try doing this instead
int myNumber = ([frequency intValue] + 1);
frequency = [NSNumber numberWithInt:myNumber];
Yes, numberWithInt: does indeed return a new object. You're probably not retaining this object. Just properly retain frequency when assigning it a new NSNumber. Without context, I'm not sure the best way to accomplish this, but one way is to make frequency a property of your object and using the accessor method.
It would seem that you've already initialized and assigned some value prior to NSNumber, like you have it inside an array for example.
Basically NSNumber objects are immutable, so changing their value is not possible anyway.
You can do it this workaround if you use it inside an array:
NSMutableArray *myOldArray = [[NSMutableArray alloc] init];
myOldInt = 3;
myOldArray[4] = [NSNumber numberWithInt:myOldInt]; // for example
NSMutableArray *myNewArray = [[NSMutableArray alloc] init];
myInt = myOldInt+2;
NSMutableArray *row = [NSMutableArray arrayWithObjects:myOldArray[1],myOldArray[2],myOldArray[3],[NSNumber numberWithInt:myInt],[NSNumber numberWithInt:myInt2],nil];
[myNewArray addObject:row];
Related
I'm new to cocoa / objective-c and i'm struggeling with the releases of my objects. I have the following code:
gastroCategoryList = [[NSMutableArray alloc] init];
for (NSDictionary *gastrocategory in gastrocategories) {
NSString *oid = [gastrocategory objectForKey:#"id"];
GastroCategory *gc = [[GastroCategory alloc] initWithId:[oid intValue] name:[gastrocategory objectForKey:#"name"]];
[gastroCategoryList addObject:gc];
}
The analyzer shows me that the "gastrocategory" defined in the for is a potential memory leak. But i'm not sure if i can release this at the end of the for loop?
Also at the following code:
- (NSArray *)eventsForStage:(int)stageId {
NSMutableArray *result = [[NSMutableArray alloc] init];
for (Event *e in eventList) {
if ([e stageId] == stageId) {
[result addObject:e];
}
}
return result;
}
The Analyzer tells me that my "result" is a potential leak. But where should I release this?
Is there also a simple rule to memorize when i should use assign, copy, retain etc. at the #property ?
Another problem:
- (IBAction)showHungryView:(id)sender {
GastroCategoriesView *gastroCategoriesView = [[GastroCategoriesView alloc] initWithNibName:#"GastroCategoriesView" bundle:nil];
[gastroCategoriesView setDataManager:dataManager];
UIView *currentView = [self view];
UIView *window = [currentView superview];
UIView *gastroView = [gastroCategoriesView view];
[window addSubview:gastroView];
CGRect pageFrame = currentView.frame;
CGFloat pageWidth = pageFrame.size.width;
gastroView.frame = CGRectOffset(pageFrame,pageWidth,0);
[UIView beginAnimations:nil context:NULL];
currentView.frame = CGRectOffset(pageFrame,-pageWidth,0);
gastroView.frame = pageFrame;
[UIView commitAnimations];
//[gastroCategoriesView release];
}
I don't get it, the "gastroCategoriesView" is a potential leak. I tried to release it at the end or with autorelease but neither works fine. Everytime I call the method my app is terminating. Thank you very much again!
In your loop, release each gc after adding it to the list since you won't need it in your loop scope anymore:
gastroCategoryList = [[NSMutableArray alloc] init];
for (NSDictionary *gastrocategory in gastrocategories) {
NSString *oid = [gastrocategory objectForKey:#"id"];
GastroCategory *gc = [[GastroCategory alloc] initWithId:[oid intValue] name:[gastrocategory objectForKey:#"name"]];
[gastroCategoryList addObject:gc];
[gc release];
}
In your method, declare result to be autoreleased to absolve ownership of it from your method:
NSMutableArray *result = [[[NSMutableArray alloc] init] autorelease];
// An alternative to the above, produces an empty autoreleased array
NSMutableArray *result = [NSMutableArray array];
EDIT: in your third issue, you can't release your view controller because its view is being used by the window. Setting it to autorelease also causes the same fate, only delayed.
You'll have to retain your GastroCategoriesView controller somewhere, e.g. in an instance variable of your app delegate.
BoltClock's answer is spot-on as to the first part of your question. I'll try to tackle the rest.
Assign is for simple, non-object types such as int, double, or struct. It generates a setter that does a plain old assignment, as in "foo = newFoo". Copy & retain will, as their names imply, either make a copy of the new value ("foo = [newFoo copy]") or retain it ("foo = [newFoo retain]"). In both cases, the setter will release the old value as appropriate.
So the question is, when to copy and when to retain. The answer is... it depends. How does your class use the new value? Will your class break if some other code modifies the incoming object? Say, for example, you have an NSString* property imaginatively named "theString." Other code can assign an NSMutableString instance to theString - that's legal, because it's an NSString subclass. But that other code might also keep its own reference to the mutable string object, and change its value - is your code prepared to deal with that possibility? If not, it should make its own copy, which the other code can't change.
On the other hand, if your own code makes no assumptions about whether theString might have been changed, and works just as well whether or not it was, then you'd save memory by retaining the incoming object instead of unnecessarily making a copy of it.
Basically, the rule, which is unfortunately not so simple sometimes, is to think carefully about whether your own code needs its own private copy, or can correctly deal with a shared object whose value might be changed by other code.
The reason you can release gc after it is added to the gastroCategoryList is that when an object is added to an array, the array retains that object. So, even though you release your gc, it will still be around; retained by the gastroCategoryList.
When you are returning a newly created object from a method, you need to call autorelease. This will cause the object to be released only after the runtime leaves the scope of the calling method, thereby giving the calling method a chance to do something with the returned value.
Note that if your method starts with the word copy or new, then you should not autorelease your object; you should leave it for the calling method to release.
As for copy vs retain vs assign... as a general rule, copy objects that have a mutable version, such as NSArray, NSSet, NSDictionary, and NSString. This will ensure that the object you have a pointer to is not mutable when you don't want it to be.
Otherwise, use retain whenever you want your class to be ensured that an object is still in memory. This will apply to almost every object except for objects that are considered parents of your object, in which case you would use assign. (See the section on retain cycles here).
Also note that you have to use assign for non-object types such as int.
Read through the Memory Management Programming Guide a bit; it's quite helpful.
ok. I have a really odd and mind boggling problem. I have two class files, both of which are NSObject inheritors. The series of code is as follows
CustomClass *obj;
obj = [[CustomClass alloc] init];
[myArray addObject:obj]; <--------Immediately after this line if I hover over the array it shows it as having 1 object that is out of scope.
If I hover over both objects they both have what look to be initialized memory locations so I really have no idea what is going on here. Thanks in advance.
UPDATE: There is a place in the code where I call a function repeatedly with a timer. Inside of the timer I do the following.
CustomClass *obj = [CustomClass alloc];
obj = [myArray objectAtIndex:0];
obj.var += 10;
[obj release];
On the line obj.var I get a EXC_BAD_ACCESS error. I am probably doing the alloc and releases incorrectly considering it is called repeatedly but I have tried everything I can think of.
I think you are referring to the XCode debugging feature which shows you the content of variables.
I did encounter the same issue as well, and what I'm sure of is that this is generally not a problem with your code.
Now what I'm not sure of is why this happens, but I believe that the variable obj in your example is not used after the call anymore. This means the compiler reuses the place where this reference was stored, thus the debugger could "lose" the pointer to your variable and it will appear as out of scope (but I am no expert in the ways of gcc or the debugger, so I could be wrong here).
This code is wrong:
CustomClass *obj = [CustomClass alloc];
obj = [myArray objectAtIndex:0];
obj.var += 10; [obj release];
What you are doing is allocing a new CustomClass (without initializing it, which should never be done), then replacing it with the object from the array (leaking the old one), and then afterwards releasing the object from the array. This will cause a crash the next time the object in the array is accessed. Instead, just say:
CustomClass *obj = [myArray objectAtIndex:0];
obj.var += 10;
Don't release unless you retain in advance. (See the Cocoa memory management guide for more information).
This isn't the problem you are referring to, but please don't do this:
CustomClass *obj = [CustomClass alloc];
Never issue an alloc without an init of some sort. Also, in the context of the code you posted it isn't required, as you assign a value to obj on the next line.
Then [obj release]; isn't required, as you haven't retained the obj value you obtain from myArray. You are probably doing it because of the preceding alloc, which as I have said isn't required.
if a reference to obj.var is causing a BAD_ACCESS, then either obj or var has been dealloced by code elsewhere, almost certainly var.
I try to understand the memory management in ObjectiveC and still some things are a misery for me.
I've got an instance variable:
NSMutableArray *postResultsArray;
when a button is clicked in the UI I create new array:
self.postResultsArray = [NSMutableArray array];
then I add some objects to the array and when the whole operation is done I would like to release the array:
[self.postResultsArray release];
(I assume that all the objects stoed in the array will be released along with the array).
The problem appears when I click the button again and in the code I want to create the array again with:
self.postResultsArray = [NSMutableArray array];
I get:
[CFArray release]: message sent to deallocated instance 0x3d9e390
Can't I initialize the same instance variable for the second time? or maybe I should not release it? and if so, why?
Thanks!
Don't to this:
[self.postResultsArray release];
When you do this, the ivar is still assigned to the old array's memory address. If you want to release the array, there are two safe ways to do it:
[postResultsArray release];
postResultsArray = nil;
Or
self.postResultsArray = nil;
What's happening is that the code for setting the postResultsArray looks like this (paraphrase, not exact):
-(void)setPostResultsArray:(NSMutableArray *)newArray {
[array retain];
[postResultsArray release]; // this is what's causing the the deallocation message in your log
postResultsArray = array;
}
You shouldn't manually release an object that is accessed through a property. Instead of
[self.postResultsArray release];
do
self.postResultsArray = nil;
and all will be fine. The setter will release the old array and then assign nil to the pointer. What is happening now is that the setter is trying to release the old array when you assign a new array to the property, but you have already released that array, hence the error.
Don't do [self.postResultsArray release];, do self.postResultsArray = nil, this has to do with the implementation of properties. They will automatically release whatever is currently stored and retain the new value.
You only need to call release if you create an object with one of the "init" messages or explicitely call retain yourself. Since you do neither you don't need to call release as the code that created the array will be handling the release - most probably by using autorelease.
I've defined a struct and want to assign one of its values to a NSMutableDictionary. When I try, I get a EXC_BAD_ACCESS. Here is the code:
//in .h file
typedef struct {
NSString *valueOne;
NSString *valueTwo;
} myStruct;
myStruct aStruct;
//in .m file
- (void)viewDidLoad {
[super viewDidLoad];
aStruct.valueOne = #"firstValue";
}
//at some later time
[myDictionary setValue:aStruct.valueOne forKey:#"key1"]; //dies here with EXC_BAD_ACCESS
This is the output in debugger console:
(gdb) p aStruct.valueOne
$1 = (NSString *) 0xf41850
Is there a way to tell what the value of aStruct.valueOne is?
Since it is an NSString, why does the dictionary have such a problem with it?
------------- EDIT -------------
This edit is based on some comments below.
The problem appears to be in the struct memory allocation. I have no issues assigning the struct value to the dictionary in viewDidLoad, as mentioned in one of the comments. The problem is that later on, I run into an issue with the struct. Just before the error, I do:
po aStruct.oneValue
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0x00000000
0x9895cedb in objc_msgSend ()
The program being debugged was signaled while in a function called from GDB.
GDB has restored the context to what it was before the call.
To change this behavior use "set unwindonsignal off"
Evaluation of the expression containing the function (_NSPrintForDebugger) will be abandoned.
This occurs just before the EXC_BAD_ACCESS:
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:#"MM-dd-yy_HH-mm-ss-A"];
NSString *date = [formatter stringFromDate:[NSDate date]];
[formatter release];
aStruct.valueOne = date;
So the memory issue is most likely in my releasing of formatter. The date var has no retain. Should I instead be doing
NSString *date = [[formatter stringFromDate:[NSDate date]] retain];
Which does work but then I'm left with a memory leak.
I recreated your code and put the NSDictionary setValue method, right under the aStruct.valueOne = #"firstValue" line. It works perfectly without any error. So, your problem is not with the NSString, but with one of the objects (either aStruct or myDictionary) getting deallocated somewhere down the line. You can try the following:
static myStruct aStruct;
To print the value of aStruct.valueOne, you may use:
NSLog(#"aStruct.valueOne = %# \n", aStruct.valueOne);
Also, you can check the retain counts of myDictionary to see if it is still allocated. However, trying to check for the retain count of an already deallocated object will result in an error. But it will tell you in the error log, that the object is already deallocated.
NSLog(#"Retain Count of myDictionary = %i \n", myDictionary.retainCount);
Hope that helps.
Not sure why it's crashing, but instead of p, use po and it will print the contents of the NSString or description of any NS/CF object.
Try to enable zombies to check where do you over-release objects. Project -> Edit Active Executable -> Arguments tab -> Add variable NSZombieEnabled and assign it YES. (and set checkbox to YES).
Then you should get more info about your error in the trace.
Don't forget to disable NSZombieEnabled checkbox then.
EDIT:
When you assign a valueOne:
aStruct.valueOne = #"firstValue";
you actually create NSString object and put it into autorelease pool. So later when you try to get that object to pass it to your dictionary, it might be autoreleased already, that's why you are getting EXC_BAD_ACCESS. You have to implement some method which will do memory management for you when you assign new pointers to your struct. Something like this:
- (void)setValueOne:(NSString *)newValueOne {
[aStruct.valueOne autorelease];
aStruct.valueOne = [newValueOne retain];
}
So in your viewDidLoad you have to use your new method:
- (void)viewDidLoad {
[super viewDidLoad];
// make sure it is nil "on startup" because setValueOne: method will send autorelease method
aStruct.valueOne = nil;
aStruct.valueTwo = nil;
[self setValueOne:#"firstValue"];
}
Any 'class *instance' is a pointer to an object. That $1 = (NSString *) 0xf41850 you see is actually the pointer to the memory space that is currently allocated to hold valueOne. The issue usually associated with EXEC BAD ACCESS is that the memory space is not permanently allocated to hold valueOne, and is reclaimed later on, usually as soon as the method finishes execution (called garbage collection). Then, when you later try to access it, like from a different method or even the same method but on a subsequent execution, the system says 'hey, that memory address is used for something else", it throws the Exec Bad Access error.
Is there a way to tell what the value
of aStruct.valueOne is?
Well, the debugger, at the moment you establish the value, should be able to pick up on the definition and show you the literal value; it should know that the memory space at 0xf41850 maps to an NSString class, which is an array of bytes of some length, and that the bytes at that address are encoded a certain way, and thus should map into some string that can be displayed on your display in the debugger. However, later on, no, the system has no (valid) idea of what that space contains, since it could contain, well, anything.
So, when you run into EXEC BAD ACCESS, it means that you are not retaining that value for long enough period, either because you have not purposely retained it, or have released it (on purpose or inadvertently let the system release it).
I'm doing an iPhone application which uses a navigation control to browse through some data. This data is stored in a sqlite database and I have a class which gets it and returns it in a NSMutableArray of NSStrings.
The problem is that in the first screen of the navigation everything works prefectly, but in the second screen (another view which is pushed) the same code fails because the NSMutableArray gets corrupted. In the debugger I can see that it is returned correctly, but when it's time to use it the pointers have become corrupted and the application crashes.
I have put breakpoints in all my functions, and I can't see anywhere where it can get corrupted. And as the first view, which uses the same exact code, even accesing the same eact tables, works correctly I don't really know where to look.
If anyone want to have a look at the code I have uploaded it to my site: http://sachafuentes.com/iBacus.zip
Thanks in advance.
UPDATE:
The problem lies in the function where I get the data, which looks like (this is a simplified version with some pseudo-code).
-(NSMutableArray *) getPaises {
NSMutableArray * paises;
paises = [[NSMutableArray alloc] init];
while( get new row ) {
NSString *aPais = get the value;
[paises addObject:aPais];
[aPais release];
}
return paises;
}
If I comment out [aPais release] everything works, but to me this looks like a memory leak, as the NSString won't be released.
Okay, here's the problem:
NSString *aPais = [NSString stringWithUTF8String:(char*)sqlite3_column_text(compiledStatement, 0)];
By convention, any time that you see an alloc and an init, you need a release somewhere down the road.
By convention, any time that you use an xWithX: style method, the resulting object will be released for you.
Therefore, this statement:
[aPais release];
will cause your method to crash, as the object is released before it should be. Just remove this line, set your NSMutableArray instance to be autorelease-d and you should get better results.
Look for wrong memory management, that's the likeliest cause for crashes. I think you release your objects somewhere where you shouldn't and therefore you have dangling pointers in the array.
Update1
[aPais release] is wrong, as you don't retain it anywhere in this method. Returned values should always be autoreleased. You should have the same amount of retain as release in your code.
(Some people argue that a retain can also be an alloc init, but I always try to use alloc init autorelease, but this is a matter of style.)
BTW
You should autorelease your array, you're only retaining it here with [[alloc] init].
Any object that you alloc and init must be release-d when you're finished with it, or you will have a memory leak.
Since you are passing the reference outside the scope of the getPaises method, you must autorelease the NSMutableArray, or you will have a memory leak:
paises = [[[NSMutableArray alloc] init] autorelease];
Can you please clarify the step here:
NSString *aPais = get the value;
It's not clear what happens in "get the value" and I suspect this is one cause of instability.
I see that the code is (verbatim)
while(sqlite3_step(compiledStatement) == SQLITE_ROW) {
NSString *aPais = [NSString stringWithUTF8String:
(char*)sqlite3_column_text(compiledStatement, 0)];
[paises addObject:aPais];
[aPais release];
}
...and it's exactly as #gs puts it. aPais is autoreleased and should not be released.
You can also use a convenience constructor to initialize the NSMutableArray:
NSMutableArray *paises = [NSMutableArray array];
This is equivalent to doing:
NSMutableArray *paises = [[[NSMutableArray alloc] init] autorelease];