I try to add object to my NSMutable array in my method, but keep getting error. It works, if I add the object in init. It doesn't say that anything is wrong until I try to execute the code.
This is below the #import stuff where I declare two arrays:
NSMutableArray *actions1, *actions2;
This is in init:
actions1 = [NSMutableArray array];
Here I try to add 1 to the array:
- (void) storeAction:(int) action {
[actions1 addObject:#"1"];
}
The same code works in int as I said earlier.
I also would like it to store the int value declared "action", but this didn't seem to work either.
[addObject:#"%d", action];
[NSMutableArray array]; is returning an autoreleased object, by the time you try to access it, it is most likely deallocated already. Try [[NSMutableArray alloc] init]; instead. And than you should urgently check the memory management rules.
Try out this code
actions1 = [[NSMutableArray alloc] init];
Hope this helps.
Alternatively, in your header file:
#property(nonatomic, strong)NSMutableArray *actions1;
Then in the implantation file:
#synthesize actions1 = _actions1;
Then you can access your array as self.actions1.
Related
I have an NSMutableArray filled with Task objects. I want to be able to delete those whose completed property are set to YES
NSMutableArray *allTasks = (NSMutableArray *)[[TaskStore defaultStore] allTasks];
NSMutableArray *completedTasks;
for (Task *task in allTasks) {
if ([task completed]) {
[completedTasks addObject:task];
}
}
[allTasks removeObjectsInArray:completedTasks];
While debugging I noticed that the completedTasks array is always empty. Why is this?
You forgot to initialize the completedTasks :
NSMutableArray *completedTasks = [NSMutableArray array];
You haven't initialized completedTasks. You need to add this:
NSMutableArray *completedTasks = [[NSMutableArray alloc] init];
You must initialize the array before you can use it, the initializing actually creates your array object -
To do this add This Line to create an autoreleased array (which means you dont have to release it)
NSMutableArray *completedTasks = [NSMutableArray array];
Or
NSMutableArray *completedTasks = [[NSMutableArray alloc] init];
But then you will have to release it by yourself [completedTasks release] when you are not using it any moere (unless you are using ARC).
This will create your array object.
Shani
from NSMutableArray documentation :
This method assumes that all elements in otherArray respond to hash and isEqual:.
You can try :
[allTasks filterUsingPredicate:[NSPredicate predicateWithFormat:#"completed = %#", [NSNumber numberWithBool:YES]]]
Can any one help me to understand the problem in this image
As the analyzer says, you are allocating locs on line 647, using
NSMutableArray *locs = [[NSMutableArray alloc] init]; and not releasing it later in the block. You should release it or you can use convenience constructor to get the autoreleased array like this, NSMutableArray *locs = [NSMutableArray array];
I'd suggest you to still simplify your code to this,
NSMutableArray *annotations = (NSMutableArray *)[map annotations];
[annotations removeObject:[map userLocation]];
[map removeAnnotations:annotations];
You need to release locs at the very end. You have alloc'ed and init'ed it, giving it a reference count of 1, an then you should release it to change the reference count to 0. Refer to http://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/MemoryMgmt/ for more info.
You have initialize the locs array then you have to release that array before closing that function: [locs release];locs=nil;
After a ASIFormDataRequest , i create a temporary NSMutableArray *resultArray from the JSON then add it to a defined NSMutablearray *myData
-(void)viewDidLoad{
myData = [[NSMutableArray alloc] init];
//request that calls gotInfo method
}
-(void)gotInfo:(ASIFormDataRequest *)request{
NSString *responseString = [request responseString];
NSMutableArray *resultArray = [responseString yajl_JSON];
[myData addObject:resultArray];
}
-(IBAction)doSomethingWithData:(id)sender{
//something with myData
}
but when i try to call myData from outside of the gotInfo: method, i get bad access errors and when i inspect myData outside of the method, it shows a kern_protection_failure. So i'm guessing that outside of the method, the resultArray is obviously released, but it's also released from myData since the object inside myData is sharing the same memory location?
I also tried
-(void)gotInfo:(ASIFormDataRequest *)request{
NSString *responseString = [request responseString];
[myData addObject:[responseString yajl_JSON]];
}
How do I preserve myData??
in my header file:
#import <UIKit/UIKit.h>
#class ASIFormDataRequest;
#interface EventsTableController : UITableViewController <UITableViewDataSource>{
NSMutableArray *myData;
}
-(void)gotInfo:(ASIFormDataRequest *)request;
UPDATE:
so in the gbd, the myData is allocated as 0x5e96560 so i did
po 0x5e96560
and then i get the EXC_BAD_ACCESS with the reason being KERN_PROTECTION_FAILURE at address: 0x00000009
but if i do
po [[0x5e96560 objectAtIndex:0] objectForKey:#"key"]
then i get the value! whyyyyyy?
#property(nonatomic,retain) NSMutableArray *myData
and create the object
self.myData = [[NSMutableArray alloc] init];
and
// and i assume your resultArray is a mature NSMutableArray object
[self.myData addObject:resultArray];
The best way of using copy I can think of, is to always set NSString properties to "copy" instead of retain. That way you get more accurate readings from the Leaks instrument if you mess up and forget to release a string an object is holding onto. Other uses of copy need to be more carefully thought out.
NOTE : You are responsible to release myData after no use of that variable.
You dont really have any way to correctly access myData as you declare it as a member inside of EventsTableController, but you dont set the #property for it, and do not synthesize it either. By synthesizing it in your EventsTableController.m file you are telling xcode to generate the getter/setters you need to correctly touch myData, which is where your program seems to be failing. If you do this, this should solve your problem.
-Karoly
Except for the different name of your ivar (mienVar vs. myVar), I don't see a problem. Some other code must be releasing your ivar, or you are accessing it before viewDidLoad has the opportunity to actually create the array (I bet it is the latter).
I think you should put the code in viewDidLoad in your initialization method instead. Don't forget to release the array in dealloc.
You could, of course, also write your own myData getter method, doing lazy initialization, instead of creating it in the init method:
- (NSMutableArray *) myData
{
if (!myData)
myData = [[NSMutableArray alloc] init];
return myData;
}
Note that now, you should access self.myData if you want to use it.
I think the NSString yajl_JSON category can return an array or a dictionary - you might need to inspect the type of the result array on the line below as it may be an NSDictionary:
NSMutableArray *resultArray = [responseString yajl_JSON];
IF you are treating it as an array when its a dictionary that might be causing your problems.
(relevant code from the NSObject+YAJL category below)
YAJLDocument *document = [[YAJLDocument alloc] initWithData:data parserOptions:options error:error];
id root = [document.root retain];
[document release];
return [root autorelease];
(and in YAJLDocument object)
#interface YAJLDocument : NSObject <YAJLParserDelegate> {
(id root_; // NSArray or NSDictionary
Hey all. I know this question's been asked but I still don't have a clear picture of memory management in Objective-C. I feel like I have a pretty good grasp of it, but I'd still like some correct answers for the following code. I have a series of examples that I'd love for someone(s) to clarify.
Setting a value for an instance variable:
Say I have an NSMutableArray variable. In my class, when I initialize it, do I need to call a retain on it?
Do I do
fooArray = [[[NSMutableArray alloc] init] retain];
or
fooArray = [[NSMutableArray alloc] init];
Does doing [[NSMutableArray alloc] init] already set the retain count to 1, so I wouldn't need to call retain on it? On the other hand, if I called a method that I know returns an autoreleased object, I would for sure have to call retain on it, right? Like so:
fooString = [[NSString stringWithFormat:#"%d items", someInt] retain];
Properties:
I ask about the retain because I'm a bit confused about how #property's automatic setter works.
If I had set fooArray to be a #property with retain set, Objective-C will automatically create the following setter, right?
- (void)setFooArray:(NSMutableArray *)anArray {
[fooArray release];
fooArray = [anArray retain];
}
So, if I had code like this: self.fooArray = [[NSMutableArray alloc] init]; (which I believe is valid code), Objective-C creates a setter method that calls retain on the value assigned to fooArray. In this case, will the retain count actually be 2?
Correct way of setting a value of a property:
I know there are questions on this and (possibly) debates, but which is the right way to set a #property?
This?
self.fooArray = [[NSMutableArray alloc] init];
Or this?
NSMutableArray *anArray = [[NSMutableArray alloc] init];
self.fooArray = anArray;
[anArray release];
I'd love to get some clarification on these examples. Thanks!
According to Apple's Object Ownership Policy, any method that begins with the words alloc or new, or contains copy is owned by the caller.
To obtain ownership of an object, you must retain it.
So, in your first example, the retain is unnecessary because you already own the object.
The correct way to do this:
fooArray = [[NSMutableArray alloc] init];
Since autoreleased objects are owned by the current autorelease pool, you must call retain on them to gain ownership of them, so this example is correct:
fooString = [[NSString stringWithFormat:#"%d items", someInt] retain];
This would work fine as well:
self.fooString = [NSString stringWithFormat:#"%d items", someInt]; //retained by property setter
And for your last example using the property setter, this would be the correct way to do it:
NSMutableArray *anArray = [[NSMutableArray alloc] init];
self.fooArray = anArray;
[anArray release];
Instead of having to do the above, I'd suggest the following solution:
self.fooArray = [NSMutableArray arrayWithCapacity:10];
arrayWithCapacity: will return an autoreleased NSMutableArray, which is the retain-ed by the property setter method. :)
Ideally you would want to use the accessors whenever possible, especially when dealing with objects as they help avoid many memory issues. So even for instance variables, you should do:
self.fooArray = ...;
instead of
fooArray = ...;
The reason why you should declare properties for object instance variables is because the memory management is slightly more complicated, and recreating it by hand each time is tricky. The correct setter for a nonatomic, retained property would look like:
- (void)setFoo:(NSArray *)aFoo {
if (foo == aFoo) {
return;
}
NSArray *oldFoo = foo;
foo = [aFoo retain];
[oldFoo release];
}
You are right about the instance variable having a retain count of 2 when you do something like this (assuming foo is retained):
self.foo = [[NSMutableArray alloc] init];
The first retain count is coming from alloc, and the second one from your synthesized setter. Any of these should work:
// longer, explicit version, releases immediately (more efficient)
NSMutableArray *aFoo = [[NSMutableArray alloc] init];
self.foo = aFoo;
[aFoo release];
// autoreleased, not so bad unless you're a memory management freak
self.foo = [[[NSMutableArray alloc] init] autorelease];
// an even shorter version of the above
self.foo = [NSMutableArray array];
To create private properties, you can declare them as a class extension in the .m implementation file. To give an example, consider a simple Person object, which has a name, and a boolean property didSave which simply indicates whether the object has been saved to some database or not. Since we don't want to expose this to the outside world, but still keep the benefits of properties inside the implementation file, we can create the header file will all instance variables (public, private, protected) and only public properties:
// Person.h
#interface Person {
NSString *name;
#private
BOOL didSave;
}
#property (nonatomic, retain) NSString *name;
#end
But declare private properties inside the implementation:
// Person.m
// property is declared as a class extension, making it
// invisible to the outside world.
#interface Person ()
#property BOOL didSave;
#end
#implementation
// synthesize as normal
#synthesize name, didSave;
#end
First of all, with this line:
fooArray = [[NSMutableArray alloc] init];
fooArray will automatically have a retain count of 1.
Second, yes, it's 2. And your guess on the setter implementation is correct.
Third, the latter one is right
I'm trying to declare a two-dimensional array as an instance variable in Objective C. I've got the NSMutableArray in the header (data), along with the #property (nonatomic, retain). In viewDidLoad: I have:
data = [[NSMutableArray alloc] init];
[data addObject:[[NSArray alloc] initWithObjects:#"Cheese", #"Meat", #"Veggie", nil]];
[data addObject:[[NSArray alloc] initWithObjects:#"Sandwich", #"Soup", #"Stew", nil]];
I can NSLog the array within the method and it is correct, however when I try to Log it from a separate method I get nothing (just "#"), and if I try to access with
NSInteger num = [[data objectAtIndex:component] count];
it crashes with no error in the log. I'm sure this is something to do with not allocating memory properly, however I am new to Obj C and haven't worked with a C-style language in many years. FWIW, I have tried many variants of this that all fail, including using NSArray instead of mutable, [NSArray arrayWithObjects] instead of [[NSArray alloc] initWithObjects], and every combination in between.
try creating the outer array like this:
self.data = [NSMutableArray arrayWithCapacity:2]; // assuming you're only adding 2 inner arrays.
The following may be a right way.
self.data = [NSMutableArray array];
[data addObject:[NSArray arrayWithObjects:#"Cheese", #"Meat", #"Veggie", nil];
[data addObject:[NSArray arrayWithObjects:#"Sandwich", #"Soup", #"Stew", nil];
Note that, as #jamihash commented above, you need self.data to properly retain the array. And, there is no need to alloc the NSArray which you are adding to data.
As a side issue, you're retaining the child arrays twice. They get retained when you add them to your NSMutableArray, so you should probably autorelease them on creation or create them with one of the NSArray methods that returns an autoreleased array.
Your code by itself shouldn't crash. You should look into where and when you release and retain the NSMutableArray. You could post more of the code and I'm sure somebody will spot the problem.