I will try to make myself as clear as possible. Let start from the beginning. I have an application with a tableview that contains a list of places with distances from myLocation. Now everytime I get an update in the gps location I run the following code
- (void)locationUpdate:(CLLocation *)location {
myLocation = location;
for (Trek * trek in list) {
CLLocation *loc = [[CLLocation alloc] initWithLatitude:[trek latitude_start] longitude:[trek longitude_start]];
double dis = [locationManager getDistance: loc];
[trek setDistance:dis];
[trek setDistanceUnit];
[loc release];
}
[self.tableView reloadData];
}
Now this piece of code [trek setDistanceUnit]; calls
-(void) setDistanceUnit {
if (self.distance < 1000.0)
self.distanceString = [NSString stringWithFormat:#"%.0lf m", self.distance];
}
Now if I use only distanceString the application crash. Now I think it may have something to do with the fact that those updates may run concurrently (in parallel) to the access required by the view to draw the cells. Anyone has any idea? I can post more code if helpful, I just didn't want to post too much to make this post too long.
I tried to search everywhere but I could not found anything so far.
Thanks in advance,
Umberto
PS Now the application is working but I would like to understand what is going on.
If your distanceString is a retain property, assigning it without self sets it up for a crash because you bypass the setter, and assign the string without retaining it. So when the string gets deallocated on being sent to the autorelease pool, your app crashes.
By synthesizing the accessors using #synthesize and using the dot notation (or setDistanceString:), the object will retain the string for you so that it always has a pointer to it for itself (until it's released).
Related
Could someone help me please understand how allocation and memory management is done and handled in following scenario. i am giving a Psuedo code example and question thats troubling me is inline below:
interface first
{ NSDecimalNumber *number1;
}
implementation
.....
-(void) dealloc {
[number1 release];
[super dealloc];
}
=================================
interface second
{ NSDecimalNumber *number2;
}
implementation second
.....
- (First*) check
{
First *firstObject = [[[First alloc] init] autorelease];
firstObject.number1 = [[NSDecimalNumber alloc] initWithInteger:0];
**// do i need to autorelease number1 as well?**
return firstObject;
}
Your code is correct as is. If you autoreleased the object, its reference count would reach zero and it would be dealloced, and then if you later tried to use the value stored in number1 your app would crash.
The only enhancement I'd add is releasing any existing value. i.e.
[number1 release];
number1 = [[NSDecimalNumber alloc] initWithInteger:0];
If you don't do this, the previous object assigned to number1 will leak each time check is called.
As you're allocing the NSDecimalNumber, you need to release it. (As you're doing so in the dealloc.)
Whilst it's hard to provide a meaningful example based on your sample code (as "number1" isn't actually used), the general rule is that you're responsible for any object you alloc, copy or new. If the object was only required in the scope of a function, you could of course autorelease it.
There's a good blog article over at http://interfacelab.com/objective-c-memory-management-for-lazy-people/ that I'd recommend reading as it provides good examples (including some edge cases) and is easy to follow.
Serious Problem here... i'm getting ECX_BAD_ACCESS if i try to NSLog an instance variable of my custom object. Following Function is called in my ViewController, payload holds String Data which is pulled from a url.
- (void) initVcardWithData:(NSString *)payload {
NSLog(#"1. initVcardWithData");
aVCard = [[vcardItem alloc] initWithPayload:payload];
VCardViewController *aVCardViewController = [[VCardViewController alloc] initWithVCard:aVCard];
[self presentModalViewController:aVCardViewController animated:YES];
[aVCard release];
}
So far so good. The initWithWithVCard function is as follows, theVCard and theVCardN are defined in #implementation and also set as a #property (nonatomic, retain) in (.h).:
-(id)initWithVCard:(vcardItem *)aVCard {
if(self = [super init]) {
theVCard = [aVCard retain];
theVCardN = [theVCard.PersonName retain];
}
NSLog(#"---- vCardViewController :: initWithVcard :: FirstName: %#", theVCard.PersonName.FirstName);
return self;
}
If i access the theVCardN object in my ViewController aVCardViewController within ViewDidLoad everything works like a charm. I set some labels with data from that object.
If i then try to access the instance variables from theVCardN within a function which is called from an IBAction which is connected to a button in View, i get an EXC_BAD_ACCESS error at the debugger console. The Function which tries to pull data from the instance variables is as follows:
-(IBAction)addressbookButtonTapped {
NSLog(#"RETAIN COUNT FOR theVCard: %i", [theVCard retainCount]);
NSLog(#"RETAIN COUNT FOR theVCardN: %i", [theVCardN retainCount]);
NSLog(#"Save to Adressbook: %#", theVCardN.FirstName);
//[self dismissModalViewControllerAnimated:YES];
}
The RetainCounter for theVCardN right before calling NSLog outputs "1". The NSLog Line then returns EXC_BAD_ACCESS in Debugger Console.
Any idea ?
Do not call -retainCount. Absolute retain counts are useless.
retainCount returns the absolute retain count of an object. The actual value will be an implementation detail that is very often completely out of your control as the system frameworks may do any number of things internally to cause the retain count to be modified in ways you don't expect.
It is useless for debugging and their are a wealth of tools that are specifically focused on tracking down these kinds of issues.
First, if there is a crash, there is a backtrace. Post it. Probably not that interesting in this case, but, still, always look to the backtrace to at least confirm that it is crashing where/how you think it is.
From the evidence posted, it sounds like theVCardN.FirstName is either set to garbage or the underlying string has been over-released. Turn on zombie detection mode and see if that is the case. Since it is crashing on FirstName, then show the code related to creating/storing the FirstName.
Also, instance variables and methods should always start with a lowercase letter; PersonName should be personName & FirstName should be firstName.
Maybe i'm reading the code wrong or misunderstanding your class structure, but it looks like you logging:
NSLog(#"Save to Adressbook: %#", theVCardN.FirstName);
Above, where you say it is still working, you are logging:
theVCard.PersonName.FirstName
Are you missing the "PersonName"? Meaning you should be logging:
NSLog(#"Save to Adressbook: %#", theVCardN.PersonName.FirstName);
For reference, I've already read:
memory management question -- releasing an object which has to be returned
iPhone: Return NSMutableArray in method while still releasing
Releasing objects returned by method
Which I thought would help :).
This app is a teaching tool and is intended to help people visualize simple genetics. Just some background so the variable names and stuff will make sense. Here's the main code that executes when the app runs:
- (void)viewDidAppear:(BOOL)animated {
ThingzCore *core = [[ThingzCore alloc] init];
ThingzThing *thing1 = [[ThingzThing alloc] init];
thing1.breed = #"AB";
thing1.pattern = #"AC";
thing1.color = #"CA";
thing1.gender = #"XY";
thing1.generation = 1;
thing1.isEgg = NO;
ThingzThing *thing2 = [[ThingzThing alloc] init];
thing2.breed = #"CD";
thing2.pattern = #"BA";
thing2.color = #"CB";
thing2.gender = #"XX";
thing2.generation = 1;
thing2.isEgg = NO;
NSLog(#"Breeding GD BR PT CL G");
ThingzThing *child = [core mateFather:thing1 withMother:thing2];
NSLog(#"Round 1: %# %# %# %# %d",child.gender,child.breed,child.pattern,child.color,child.generation);
sleep(10);
child = [core mateFather:thing1 withMother:thing2];
NSLog(#"Round 2: %# %# %# %# %d",child.gender,child.breed,child.pattern,child.color,child.generation);
sleep(10);
child = [core mateFather:thing1 withMother:thing2];
NSLog(#"Round 3: %# %# %# %# %d",child.gender,child.breed,child.pattern,child.color,child.generation);
sleep(10);
child = [core mateFather:thing1 withMother:thing2];
NSLog(#"Round 4: %# %# %# %# %d",child.gender,child.breed,child.pattern,child.color,child.generation);
sleep(10);
[thing1 release];
[thing2 release];
[core release];
}
And here's what happens when I run it in various ways:
Running without breakpoints, it crashes, with no console message, after the 2nd sleep() but before the "Round 3" NSLog.
Running with breakpoints enabled, but none defined, it runs through the entire sequence. After the fourth sleep(), it crashes with EXC_BAD_ACCESS.
Running with breakpoints enabled and NSZombiesEnabled, it does the same thing as above - no further information, just EXC_BAD_ACCESS.
Running in Instruments, no leaks are shown.
This is the routine being called four times:
-(ThingzThing *)mateFather:(ThingzThing *)father
withMother:(ThingzThing *)mother {
// will we be doing a mutation?
int mutationPercentage = father.generation + mother.generation;
int mutationNumber = (arc4random() % ((unsigned)100 + 1));
BOOL isMutation = NO;
if (mutationNumber <= mutationPercentage) {
isMutation = YES;
}
// get possibilities
NSArray *possibilities = [self possibilitiesByMatingFather:father
withMother:mother
mutations:isMutation];
// randomly select one of the possibilities
int keeping = (arc4random() % ((unsigned)[possibilities count]));
return [possibilities objectAtIndex:keeping];
}
Without pasting in the ENTIRE code, the possibilitiesByMatingFather:withMother:mutations function is returning an NSMutableArray. That routine declares the array by using:
NSMutableArray *possibilities = [NSMutableArray array];
It then:
return possibilities;
It does not send a release or autorelease message to possibilities; my understanding is that creating the array the way I have is an implicit autorelease. I didn't want to alloc the array, because I'm returning it, so wouldn't have the opportunity to explicitly release it.
The objects held in the possibilities NSMutableArray are of a custom class. They are added as follows:
ThingzThing *newThing = [[ThingzThing alloc] init];
newThing.breed = choiceBreed;
newThing.gender = choiceGender;
newThing.color = choiceColor;
newThing.pattern = choicePattern;
newThing.generation = mother.generation + father.generation;
newThing.name = #"";
newThing.isEgg = YES;
[possibilities addObject:newThing];
[newThing release];
Which seems to work most of the time. At least, when breakpoints are enabled, the program runs through the code without complaint until the end, as noted above.
Any suggestions on what I'm doing wrong, here? It's obviously memory management issues of some kind, but I can't sort it in my head.
BTW, in a vain, throwing-things-at-the-wall attempt to figure it out, I did modify the one line from the main routine as follows:
// get possibilities
NSArray *possibilities = [[self possibilitiesByMatingFather:father
withMother:mother
mutations:isMutation] retain];
To no avail. Same results. So the problem isn't in retaining the array returned by possibilitiesByMatingFather:withMother:mutations. Forcing a retain on that return isn't helping.
Frequently in this type of situation, the actual error is not at the location shown in the debugger when the app halts.
For example, the debugger may be pointing to a method call, but the problem actually occurs inside the method -- not when the method is called.
To track things down, I would suggest setting a breakpoint just before the method call that triggers the error -- in your case, this would be the mateFather: withMother: call. Then step into that method. There is a good chance you will find that the problem happens inside that method -- or even inside a method called from within that method.
Check you have the correct property declarations of the string properties of class ThingzThing.
e.g.
#property (nonatomic, retain) NSString* breed;
NEED to be retain or copy NOT assign...
Found it. Buried eight method calls down, I was sending release to an NSArray that was obviously autoreleasing. When the initial calling routine (viewDidAppear) fell down into autorelease mode, it tried to autorelease the already-released object, and exploded. Good grief - is there any way XCode could have helped me track that down?
In any event, in case anyone runs across this, make bloody sure you're not sending a release message to something that you didn't explicitly alloc yourself. If you didn't alloc it, odds are it was autoreleasing itself, and you sending a release to it takes the retain count negative, and the Foundation framework vomits with an EXC_BAD_ACCESS.
I've spent about 10 hours trying to find this bug that was causing my app to crash, and it was in the last place I looked (well it would have been, but last place I ever expected it to be).
Originally I thought I had memory management issues (unbalanced retain/release) because the crash would happen every time I sent -removeAllObjects to an NSMutableArray filled with my custom objects. The crash wouldn't happen the first time -removeAllObjects was called. I could clear the array once, repopulate it, and then on the second clear, I would get a EXC_BAD_ACCESS. This is when my array got populated with 3 objects on the first "cycle", and 3 again on the second "cycle". When I was storing only 1 object in the array in each cycle it took 4 cycles to crash (on the 4th call of -removeAllObjects).
I FINALLY realised that the crash would go away if I changed the -init method of my custom object. Here's the -init implementation; all 4 ivars are synthesized properties with (nonatomic, retain), all of type (NSString *) except for icon which is an (NSNUmber *)
-(id)init {
if (self = [super init]) {
ip = #"";
mac = #"";
vendor = #"";
icon = [NSNumber numberWithInt:0];
}
return self;
}
Changing it to this fixed the bug:
-(id)init {
if (self = [super init]) {
self.ip = #"";
self.mac = #"";
self.vendor = #"";
self.icon = [NSNumber numberWithInt:0];
}
return self;
}
I've read that one should't use the accessors in the -init method because it can cause trouble (e.g. with subclassing).
If someone could explain to me why my bug goes away when I use accessors I would be so incredibly grateful! Seriously this has been driving me nuts, was up till 5am last night because of this.
You are assigning, but not retaining, the instance variables directly. When you use the dot syntax, you are triggering the retain part of the synthesized property and, thus, are retaining them.
-(id)init {
if (self = [super init]) {
ip = #"";
mac = #"";
vendor = #"";
icon = [[NSNumber numberWithInt:0] retain];
}
return self;
}
That should likely fix the problem (though, I'm slightly surprised, I thought 10 was still in NSNumber's instance cache. Maybe not.).
Technically you should also retain the #"" strings, but you can get away with not doing so because such strings are a special cased constant string that comes out of the compiled executable (as a private subclass of NSString that overrides to not respond to retain/release/autorelease).
The memory management guide covers this in detail. For anyone new to the platform, I would suggest re-reading it once a month (no, really -- interleaving your coding with an occasional re-read of the docs will often reveal subtle details that you didn't have enough experience to grok before. I still re-read the basic guides on a semi-annual basis.)
Ok, so I’m having this problem. What I want to do is manually add multiple annotations to a map. When I add just one annotation, it works flawlessly. The pin drops, you can click on it to see its callout, life is good.
The problem comes when I want to add more than one. When I add the second, suddenly the pin’s aren’t coloured correctly (i.e. depending on their magnitude they should be a certain color, but they’re now both the same…), and more importantly when you click on them, to see their callout, the app crashes with exex_bad_access. I really have no idea what’s wrong, maybe I’m adding too many views to the map? But it’s only 9 pins and the pins themselves add just fine.
Here’s my code…
- (void)viewDidLoad {
[super viewDidLoad];
NSMutableArray *stops = [[NSMutableArray alloc] init]; //Get list of all the stops available
Bus *bus1 = [[Bus alloc] init]; // Bus 1 holds the stops
stops = [bus1 returnStops];
for (NSString *stop in stops) //Go through each stop to add annotation to map
{
Bus *bus2 = [bus1 initWithStop:stop]; //Create an instance of bus with a given stop
MapAnnotation *eqAnn = [MapAnnotation annotationWithBus:bus2];
[self.mapView addAnnotation:eqAnn]; //Add the annotation to the map
//[eqAnn release];
//[bus2 release];
}
[self recenterMap];
[stops release];
}
- (MKAnnotationView *)mapView:(MKMapView *)mapView
viewForAnnotation:(id <MKAnnotation>)annotation {
MKAnnotationView *view = nil;
if(annotation != mapView.userLocation) {
MapAnnotation *eqAnn = (MapAnnotation*)annotation;
view = [self.mapView dequeueReusableAnnotationViewWithIdentifier:#"busLoc"];
if(nil == view) {
view = [[[MKPinAnnotationView alloc] initWithAnnotation:eqAnn
reuseIdentifier:#"busLoc"] autorelease];
}
CGFloat magnituide = [eqAnn.bus.magnitude floatValue];
if(magnituide >= .80f) {
[(MKPinAnnotationView *)view setPinColor:MKPinAnnotationColorRed];
} else if(magnituide >= .60f) {
[(MKPinAnnotationView *)view setPinColor:MKPinAnnotationColorPurple];
} else
{
[(MKPinAnnotationView *)view setPinColor:MKPinAnnotationColorGreen];
}
[(MKPinAnnotationView *)view setAnimatesDrop:YES];
[view setCanShowCallout:YES];
}
return view;
}
even tried removing the second function, but it didn’t do anything.
Thanks for the help!
P.S I should also add, there’s usually one or two pins out of the 9 which works when you click the annotation…
If i even try to manually just two annotations by hand in the program (i.e., remove the loop), it still fails and the color is still wrong...
It would appear that your memory management of the stops variable is incorrect. You allocate a mutable array, then replace that array with the return value of -[Bus returnStops], then release that. Also it's not clear what's going on with bus2 - does -[Bus initWithStop:] return a different instance of Bus? It's not usual to send any method -init* on an already-initialised object. I think that you probably are confused by the memory management conventions in Cocoa Touch. Here's a collection of articles and other references on Cocoa memory management (which is the same beast).
Have you tried using AddAnnotations instead of add annotation? - (void)addAnnotations:(NSArray *)annotations. This might work for you...but looking at the answer above and further inspection you are having some memory managment issues in your viewDidLoad (though thi s might not be the cause of your problem, but it could be). First of you are allocating the array (stops) and then ovveriding it with some array in the Bus object, this will cause a leak. Also you are then releasing that array which might be causing the crash since you are releasing the array that is actually in the Bus object w ithout having increased a reference count to it. I am not sure what initWithStop is doing but you might be getting a leak here too if initWithStop retains the object.
I wouldn't call it a memory management problem -- I'd just say you are using array references incorrectly.
After constructing the array with NSMutableArray *stops = [[NSMutableArray alloc] init], the next step is to use [stops addObject: ] to add each stop you want to store.
After that? It's not clear what you are really trying to do.
SO the answer was that I kept sending bus1 the init object, so it got confused.
"Hi David,
Your data model looks hosed to me. You only have one bus object that you are repeatedly sending initWithStop: to.
Hope this helps.
Good luck!
"
Thank you guys for your help! You all helped me quite a bit!