Although experienced with OOP, I am an absolute newbie with Objective-C. I have the following code:
// header files have been imported before this statement...
CCSprite *treeObstacle;
NSMutableArray *treeObstacles;
#implementation HelloWorldLayer {
}
-(id) init
{
// create and initialize our seeker sprite, and add it to this layer
treeObstacles = [NSMutableArray arrayWithObjects: nil];
for (int i=0; i<5; i++) {
treeObstacle = [CCSprite spriteWithFile: #"Icon.png"];
treeObstacle.position = ccp( 450-i*20, 100+i*20 );
[self addChild:treeObstacle];
[treeObstacles addObject: treeObstacle];
}
NSLog (#"Number of elements in array = %i", [treeObstacles count]);
return self;
}
- (void) mymethod:(int)i {
NSLog (#"Number of elements in array = %i", [treeObstacles count]);
}
#end
The first NSLog() statement returns "Number of elements in array = 5". The problem is that (although treeObstacles is a file-scope variable) when calling the method "mymethod", I'll get an EXC_BAD_ACCESS exception.
Can anybody please help me?
Thanks a lot
Christian
you created treeObstacles by
treeObstacles = [NSMutableArray arrayWithObjects: nil];
which will return an autoreleased object, and you didn't retain it so it will be released soon
you have to retain it by calling retain on it
[treeObstacles retain];
of simple create it by
treeObstacles = [[NSMutableArray alloc] init];
and you need to remember to release it when done like
- (void)dealloc {
[treeObstacles release];
[super dealloc];
}
you need to read more about management in Objective-C
https://developer.apple.com/library/mac/#documentation/General/Conceptual/DevPedia-CocoaCore/MemoryManagement.html
or use ARC so no need to worry retain/release anymore
http://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html
another problem, you need to call [super init] in your init method
- (id)init {
self = [super init];
if (self) {
// your initialize code
}
}
otherwise your object won't initialize properly
Related
Note: This question has been updated with suggestions supplied in answers below in which to bring a fuller context to the present state of the problem.
You may view complete project files here: https://github.com/cxx6xxc/Skeleton/blob/master/README.md
Conditions
I create an NSArray in an object's init method.
I return the NSArray with it's get method.
Problem
Upon arrival, the NSArray is null.
Creating instance
Attempt 1:
This is my original implementation.
- (id)init:
{
labels = [NSArray arrayWithObjects:#"Red", #"Green", #"Blue", nil];
return self;
}
Attempt 2:
Ismael suggested I wrap it with a sub-classing protocol.
neo suggested I retain the NSArray.
- (id)init:
{
self = [super init];
if (self)
{
labels = [NSArray arrayWithObjects:#"Red", #"Green", #"Blue", nil];
[labels retain];
}
return self;
}
Attempt 3:
Anoop Vaidya suggested I force ownership with alloc and NSMutableArray:
- (id)init:
{
self = [super init];
if (self)
{
labels = [[NSMutableArray alloc] initWithObjects:#"Red", #"Green", #"Blue", nil];
}
return self;
}
But, when I return the object, despite the different init suggestions cited above...
Returning the object
- (NSArray *)getLabels
{
return labels;
}
...with NSMutableArray...
- (NSMutableArray *)getLabels
{
return labels;
}
... the NSArray getter returns a null object.
Calling the method
int main(void)
{
id view;
view = [ZZView alloc];
id model;
model = [ZZModel alloc];
id controller;
controller = [[ZZController alloc] init: model: view];
labels = [[controller getModel] getLabels];
if(labels)
NSLog(#"allocated");
else
NSLog(#"not alloced");
[view dealloc];
[model dealloc];
[controller dealloc];
return EXIT_SUCCESS;
}
Question
What am I not doing, missing or what am I doing wrong that causes the null return value?
init methods need to call some [super init], so you will need to do something like this:
- (id)init
{
self = [super init];
if (self) {
labels = [NSArray arrayWithObjects:#"Red", #"Green", #"Blue", nil];
}
return self;
}
Edit: looking at your git repo, I found
controller = [[ZZController alloc] init: model: view];
I'm not entirely sure how the compiler interprets the empty arguments, but my guess is that it reads them as nil, and therefore your ZZController doesn't have model
Also, you have some messy argument order, the first argument (with text init:) is your model, and your second argument (with text model:) is your view
(this according to your - (id)init: (ZZModel*)Model: (ZZView*)View
In order to make it work quickly, you should do
controller = [[ZZController alloc] init:model model:view];
I'm gonna take a (short) leap here and guess you are new to iOS development, so I'll recommend that you read about objc programming, how to write functions, how to send multiple parameters, so on and so forth, and after that, do some refactoring
Cheers!
I suggest you put a breakpoint in both your init and getLabels methods, and check the value of the instance variable that stores the array: you'll see which method does not behave as expected.
Assume you are not using ARC nor synthesising variable labels, you need to retain the array,
- (id)init:
{
labels = [NSArray arrayWithObjects:#"Red", #"Green", #"Blue", nil];
[labels retain];
return self;
}
Also, you need to release it when not using the array to prevent memory leakage.
You can do it in this way, hoping in .h you have NSMutableArray *labels; :
- (id)init{
if (self = [super init]) {
labels = [[NSMutableArray alloc] initWithObjects:#"Red", #"Green", #"Blue", nil];
}
return self;
}
The init method to model was never called, it is only allocated. Therefore, NSArrray labels doesn't exist, because it is created in the init method.
// AClass.m
// init
enemyBullets = [[NSMutableArray alloc] initWithCapacity:0];
enemy1 = [[Enemy alloc] initWithBullets:enemyBullets];
// At some point
NSMutableArray *bulletsToDelete = [NSMutableArray array];
for(BulletEnemy *thisBullet in enemyBullets)
{
// If I have to delete
[bulletsToDelete addObject: thisBullet];
}
[enemyBullets removeObjectsInArray:bulletsToDelete];
//dealloc method
[enemyBullets release];
[enemy1 release];
Now Inside Enemy some point in time I do the following:
// Enemy.m
- (id)initWithBullets:(NSMutableArray*) _bullets{
// Enemybullets is a var of Enemy
enemyBullets = _bullets;
}
// At some point...
myBullet = [[BulletEnemy alloc] init];
[enemyBullets addObject:myBullet];
[myBullet release];
The problem is when I do the following at Aclass:
[enemyBullets removeObjectsInArray:bulletsToDelete];
The dealloc method inside BulletEnemy doesn't get called because the retain count isn't 0. Why? But If I release ACLass (which releases enemyBullets) then My bullets get deallocated.
Make Enemy own the enemyBullets. And use reverseObjectEnumerator
// AClass.m
// init
enemy1 = [[Enemy alloc] init];
// At some point
for(BulletEnemy *thisBullet in enemy1.enemyBullets.reverseObjectEnumerator)
{
// If I have to delete
[enemy1.enemyBullets removeObject:thisBullet];
}
//dealloc method
[enemy1 release];
//Enemy.h
#property (retain) NSMutableArray* enemyBullets;
// Enemy.m
#synthesize enemyBullets = _enemyBullets;
- (id)init{
// Enemybullets is a var of Enemy
_enemyBullets = [[NSMutableArray alloc] init];
}
// At some point...
myBullet = [[BulletEnemy alloc] init];
[enemyBullets addObject:myBullet];
[myBullet release];
-(void) dealloc{
[_enemyBullets release];
}
Aparently, I was asigning something with retain propery, which made the object +1 thus not to deallocate. Just changed the propery to assign and it worked.
I'm totally stumped on this one. I have an NSMutableArray which is declared in my header and set as a property, synthesized etc. I then call a function that allocates and initializes the array, and I add custom objects to it. I do a for each loop after the objects are added to ensure that they are actually contained within the array and they are. Once the program goes outside of this function scope, though, suddenly the array is empty.
header file:
#interface ScheduleViewController : UITableViewController {
NSString *login_id;
NSMutableArray *events;
}
- (id)initWithID:(NSString*)l_id;
- (void)grabURLInBackground; // ASIHTTP example method
#property (nonatomic, retain) NSString *login_id;
#property (nonatomic, retain) NSMutableArray *events;
#end
implementation:
#synthesize events;
- (void)requestFinished:(ASIHTTPRequest *)request
{
// Use when fetching text data
NSString *response = [request responseString];
SBJsonParser *parser = [[SBJsonParser alloc] init];
NSArray *eventDics = [parser objectWithString:response error:nil]; // an array of dictionaries of events
NSDateFormatter *dateForm = [[NSDateFormatter alloc] init];
// Allocate empty event object and initialize the mutable array
Event* event = [[Event alloc] init];
self.events = [[NSMutableArray alloc] initWithCapacity:[eventDics count]];
// loop through the array of dictionaries
for (int i = 0; i < [eventDics count]; i++)
{
NSDictionary *dict = [eventDics objectAtIndex:i];
for(NSString *key in dict) {
// for the sake of readability i wont include the code
// but the event is populated here
}
[self.events addObject:event];
[event release];
}
NSLog(#"Array Count: %i", [self.events count]);
for (Event *e in events) {
NSLog(#"eventid: %i, type: %#, price: %f, name: %#", e.event_id, e.type, e.price, e.name);
}
[parser release];
[dateForm release];
}
So the above code works fine and prints out the variables from the Event objects that are stored in the events mutable array.
What I want to do is use the events array in another function now, and when I try to, the count is 0 and also no objects are stored in the array when I look at it.
In viewDidUnload I set self.events = nil; and in dealloc I do [self.events release]
You are doing your alloc/init for the Event *event object outside of your for loop. This means you are adding the same object every time you add it to the array. You should move this line:
Event* event = [[Event alloc] init];
To the inside of your
for (int i=0 ... loop.
Not sure that would explain the symptoms you are seeing, but it could, since the following statement:
[event release]
is also releasing that one allocated object once for every time through the loop - so you are releasing the object multiple times. If you move the Event alloc to the inside of the loop then the release will be ok. (adding the object to the array will retain it so its ok to release it, but you need to allocate a new Event each time through the loop).
Basically your code should look like this: (note I've also added an autorelease to your array alloc).
// Allocate empty event object and initialize the mutable array
self.events = [[[NSMutableArray alloc] initWithCapacity:[eventDics count]] autorelease]; // assigning to the retain property will retain it, so autorelease it or it will be retained twice. Could also have used the arrayWithCapacity convenience method here instead and then wouldn't need to autorelease.
// loop through the array of dictionaries
for (int i = 0; i < [eventDics count]; i++)
{
Event* event = [[Event alloc] init]; // Allocate a new Event each time through the loop so you are adding a unique object to the array each time.
NSDictionary *dict = [eventDics objectAtIndex:i];
for(NSString *key in dict) {
// for the sake of readability i wont include the code
// but the event is populated here
}
[self.events addObject:event];
[event release];
}
I see many problems with this code. These include the fact that you are releasing objects at inappropriate times, and that you are getting confused about the scope of different objects. It seems to me that one of the biggest problems that you are having is re-allocating your events array every time the requestFinished: method is called. In your init method, you should do something like this:
- (id)init {
if ((self = [super init])) {
// Since it is a retain property, we should autorelease it when
// assigning to it, thus preventing an extra retain.
self.events = [[[NSMutableArray alloc] initWithCapacity:[eventDics count]] autorelease];
}
}
With that being said, here is how I would rewrite your requestFinished: method, as well as your dealloc method:
- (void)requestFinished:(ASIHTTPRequest *)request {
NSString *response = [request responseString];
SBJsonParser *parser = [[SBJsonParser alloc] init];
NSArray *eventDics = [parser objectWithString:response error:nil]; // an array of dictionaries of events
NSDateFormatter *dateForm = [[NSDateFormatter alloc] init];
// Clear the already allocated events array
[self.events removeAllObjects];
for (int i = 0; i < [eventDics count]; i++) {
// note how I assign event in here
Event *event = [[Event alloc] init];
NSDictionary *dict = [eventDics objectAtIndex:i];
for (NSString *key in dict) {
// Do whatever it is you do here
}
[self.events addObject:event];
[event release];
}
NSLog(#"Array Count: %i", [self.events count]);
for (Event *e in events) {
NSLog(#"eventid: %i, type: %#, price: %f, name: %#", e.event_id, e.type, e.price, e.name);
}
[parser release];
[dateForm release];
}
Finally, you can simply set the events property to nil in the dealloc method:
- (void)dealloc {
self.events = nil;
[super dealloc];
}
The only reason that I can think of for the array being empty is that a) it's contents are being deallocated, or b) it itself is being deallocated and set to nil. The pieces of your code that I fixed could possibly cause both of these. Try the changes that I have made, and see if they make a difference.
So I figured out the problem and it's due to an error on my part. After stepping through the function calls more closely, it turns out that the table view delegate method
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
was being called before populating the array with requestHasFinished. I was calling requestHasFinished indirectly through viewDidLoad but I think that the table view delegate method was being called when the view controller is initialized. Init was being called before viewDidLoad because the view controller is actually handled within a tab view controller which initializes all of the view controllers for each tab at the time when itself is initialized. That's another matter to get into.. I'm not sure if I like everything being initialized and setup before the views are even displayed but.. something to research.
Anyways thanks again for the help.
I just ran my app through the Leaks in Instruments and I am being told that the following code causes leaks, but I don't see how.
I allocate some NSMutableArrays in my viewDidLoad with this code:
- (void)viewDidLoad {
[super viewDidLoad];
self.currentCars = [[NSMutableArray alloc] init];
self.expiredCars = [[NSMutableArray alloc] init];
}
Then I populate these arrays inside of my viewWillAppear method with the following:
[self.currentCars removeAllObjects];
[self.expiredCars removeAllObjects];
for (Car *car in [self.dealership cars]) {
if ([car isCurrent])
[self.currentCars addObject:car];
if ([car isExpired])
[self.expiredCars addObject:car];
}
And later in the code I release these arrays here:
- (void) viewWillDisappear:(BOOL)animated {
if (currentCars != nil) {
[currentCars release], currentCars = nil;
}
if (expiredCars != nil) {
[expiredCars release], expiredCars = nil;
}
[super viewWillDisappear:animated];
}
Any ideas? Thanks!
Your leak is here:
self.currentCars = [[NSMutableArray alloc] init];
self.expiredCars = [[NSMutableArray alloc] init];
Assuming that you declared property accessores like this:
#property(nonatomic, retain) NSMutableArray *currentCars;
#property(nonatomic, retain) NSMutableArray *expiredCars;
In my opinion, the best way to find leaks (other than using Instruments) is to keep track of the retain count manually.
If you were to do that with for example currentCars, you would find your leak easily. Here is what happens:
self.currentCars = [[NSMutableArray alloc] init];
// The 'init' makes the retain count 1.
// 'self.currentCars = ..' translates to the setCurrentCars: method.
// You probably did not implement that method yourself,
// but by synthesizing your property it is automatically implemented like this:
- (void)setCurrentCars:(NSMutableArray *)array {
[array retain]; // Makes the retain count 2
[currentCars release];
currentCars = array;
}
// In your viewWillDisappear: method
[currentCars release], currentCars = nil; // Makes the retain count 1 so the object is leaked.
The solution is simple. Use this:
NSMutableArray *tempMutableArray = [[NSMutableArray alloc] init];
self.currentCars = tempMutableArray;
[tempMutableArray release];
A little sidenote. You shouldn't release your objects in viewWillDisappear:. The recommended place to do that is dealloc. So your code would be:
- (void)dealloc {
[currentCars release], currentCars = nil;
[expiredCars release], expiredCars = nil;
[super dealloc];
}
The problem is (probably) that you are using the property accessors for the initial setting of the arrays in -viewDidLoad. Since well-implemented property accessors will retain the object, you are getting 1 retain from the +alloc and another retain from assigning it. To fix this, you should release your arrays after assigning them or use [NSMutableArray array] to get an autoreleased one to use for your initial assignments.
Unless you're doing something very odd in currentCars, expiredCars, dealership or cars, no, there's no leak there.
Instruments' pointer to the location of a leak isn't necessarily where the object is actually leaked, per se. If I were to guess, I'd say you're probably neglecting to release either currentCars or expiredCars in your dealloc method.
Hi i'm a objC noob. I have a problem filling an NSMutableArray with objects.
for(id p in tmpArray){
Person *person = [[Person alloc] init];
person.usrName = p;
[persons addObject:person]; // after this line the persons
// array is still empty
[person release];
}
Persons is a property NSMutableArray and the problem is that it's empty. Is it the release of the person object too early or have I instanciated it wrong?
You need to initialize your array in the -init method, like this:
NSMutableArray *array = [[NSMutableArray alloc] init];
self.persons = array; // will be automatically retained
// because you're using the property
[array release]; // we alloced - we release it
Don't forget to release it:
-(void)dealloc {
self.persons = nil; // previous value of property 'persons' will be released
[super dealloc];
}
Make sure you've alloced and initialised the array before you try to add things to it