I am using the iPhone SDK and have an issue doing something simple. I am trying to add an NSNumber object to an NSMutableArray instance variable. I tried adding NSNumber card to NSMutableArray viewedCardsArray, however without breaking, it does not get added to the array. Here is the code.
/////////////////////////////////////////////////////
// Inside the header file Class.h
#interface MyViewController : UIViewController {
NSMutableArray *viewedCardsArray;
//snip ...
}
#property (nonatomic, retain) NSMutableArray *viewedCardsArray;
#end
/////////////////////////////////////////////////////
// Inside the methods file Class.m
#import "StudyViewController.h"
#implementation StudyViewController
#synthesize viewedCardsArray
//snip ...
- (IBAction)doShowCard {
//snip ...
NSNumber *cardIdObject = [[NSNumber alloc] initWithInt:(int)[self.currentCard cardId]];
[viewedCardsArray addObject: cardIdObject];
[cardIdObject release];
}
So this code executes, and does not seem to leak (according to the Leaks performance tool). However when stepping through the code, at no point does CardIdObject appear in viewedCardsArray.
Looking through SO, I know these basic questions are pretty common to ObjC newbies (like me) so apologies in advance!
Have you initialized your viewedCardsArray? If not you need to somewhere - this is usually done in the init method for your class:
- (id)init
{
self = [super init];
if(self) {
viewedCardsArray = [[NSMutableArray alloc] init];
}
return self;
}
Then it is released in the dealloc method:
- (void)dealloc
{
[viewedCardsArray release];
[super dealloc];
}
Perspx has outlined one way of initializing the array. However, you can also use the class methods provided by NSArray:
self. viewedCardsArray = [NSMutableArray array];
This can go in init or elsewhere.
Note: The object will be autoreleased.
Related
Very simple question. Is it possible to create a class which is a list by it self? I mean:
I do
taskList *taskList1 = [[taskList alloc] init];
And than simply:
taskList1 addObject:[task1]
May seem stupid, but I'm totally new to O-C syntax
I'd need two methods:
-(instancetype) init;
which just initialize as an empty list
+(instancetype)taskList;
to allocate taskList instance
and last thing:
In interface i use:
#interface taskList : NSObject
or
#interface taskList : NSMuttableArray
I got stuck on something specific, didn't I? I'm sorry that I bother you with my programming level.
Alright, I gave up, just last question, because I have to finish it very soon.
I changed my approach I added
#property NSMutableArray *list;
Why does this:
taskList *TL1 =[taskList initTaskList];
task *task1 = [[task alloc] init];
task *task2 = [[task alloc] init];
TL1.list addObject:[task1];
doesn't work, I have "Expected identifier" Error
If you read the subclassing notes on NSArray / NSMutableArray you'll see that Apple recommend against subclassing them because they are a class cluster. (i.e. what you really get when you ask for one is an undocumented subclass, and the initialiser decides which undocumented subclass to return to you based on some undocumented qualifiers..
So just make an NSObject subclass which owns a (private) strong property of type NSMutableArray, and publish an api to access that array..
eg
#import "modelList.h"
//dont worry header is empty, its up to you to do that.. this is a subclass on NSObject
#interface modelList()
#property (strong, nonatomic) NSMutableArray *backingArray;
#end
#implementation modelList
#synthesize backingArray = _backingArray;
-(instancetype )init{
if (self = [super init]) {
[self setBackingArray:[[NSMutableArray alloc]init]];
}
return self;
}
//public API (the stuff that is prototyped in the header..)
-(id)objectAtIndex:(NSUInteger )index{
return [self.backingArray objectAtIndex:index];
}
-(BOOL )containsObject:(id)object{
return [self.backingArray containsObject:object];
}
-(void )addObject:(id)object{
//example application, qualifying object..
if ([object conformsToProtocol:#protocol(NSCoding)]) {
[self.backingArray addObject:object];
}
}
-(NSUInteger )count{
return [self.backingArray count];
}
//etc etc declare publicly the things you need to get the job done
#end
so far this is just a face for a mutable array obviously, but it gives you a place for whatever other model logic you need. good luck
After many hours wasted, I officially turn to the experts for help!
My problem lies with using a NSMutableArray as an instance variable, and trying to both add objects and return the array in a method in my class. I am obviously doing something fundamentally wrong and would be grateful for help...I have already tried all the suggestions from other similar questions on stackoverflow, read apples documentation, and basically all combinations of trial and error coding I can think of. The mutable array just alway returns (null). I've even tried creating properties for them, but still the array returns (null) and then I also am running into memory management problems due to the retain while setting the property, and the init in the init method for the class.
Here is what I am trying to do:
1) Loop through a series of UISwitches and if they are 'switched on', add a string to the NSMutableArray
2) Assign this mutable array to another array in another method
Any help much appreciated,
Andy
And for some code...
fruitsViewController.h
#import <UIKit/UIKit.h>
#interface fruitsViewController : UIViewController
{
NSMutableArray *fruitsArr;
UISwitch *appleSwitch;
UISwitch *orangeSwitch;
}
#property (nonatomic,retain) NSMutableArray *fruitsArr; // ADDED ON EDIT
#property (nonatomic,retain) IBOutlet UISwitch *appleSwitch;
#property (nonatomic,retain) IBOutlet UISwitch *orangeSwitch;
- (IBAction)submitButtonPressed:(id)sender;
#end
fruitsViewController.m
#import "fruitsViewController.h"
#implementation fruitsViewController
#synthesize fruitsArr; // ADDED ON EDIT
#synthesize appleSwitch, orangeSwitch;
/* COMMENTED OUT ON EDIT
-(id)init
{
if (self = [super init]) {
// Allocate memory and initialize the fruits mutable array
fruitsArr = [[NSMutableArray alloc] init];
}
return self;
}
*/
// VIEW DID LOAD ADDED ON EDIT
- (void)viewDidLoad
{
self.fruitsArr = [[NSMutableArray alloc] init];
}
- (void)viewDidUnload
{
self.fruitsArr = nil;
self.appleSwitch = nil;
self.orangeSwitch = nil;
}
- (void)dealloc
{
[fruitsArr release];
[appleSwitch release];
[orangeSwitch release];
[super dealloc];
}
- (IBAction)submitButtonPressed:(id)sender
{
if ([self.appleSwitch isOn]) {
[self.fruitsArr addObject:#"Apple"; // 'self.' ADDED ON EDIT
}
if ([self.orangeSwitch isOn]) {
[self.fruitsArr addObject:#"Orange"; // 'self.' ADDED ON EDIT
}
NSLog(#"%#",self.fruitsArr); // Why is this returning (null) even if the switches are on?!
[fruitsArr addObject:#"Hello World";
NSLog(#"%#",self.fruitsArr); // Even trying to add an object outside the if statement returns (null)
}
#end
It seems like your init function is never called. If you're initializing this view controller from a NIB, you need to use initWithCoder. If not, just declare your fruitsArr in viewDidLoad.
Use view did load instead of init...
- (void)viewDidLoad
{
fruitsArr = [[NSMutableArray alloc] init];
}
Change that init for viewDidLoad and see what happens
Is your init method ever being called (in complicationsViewController). Add a NSLog to check this, you might be calling initWithNib: maybe.
At viewDidUnload you should remove self.fruitsArr = nil;, or, if you want to keep it, then initialize the fruitsArr in viewDidLoad (and remove it from init).
because fruitsArr don't be init.
you should do this first:
fruitsArr = [[NSMutableArray alloc] init];
so, I think you don't run - (id)init before you use fruitsArr.
A really strange problem. I have to init an array in - (void)viewDidLoad.
The array, prjMemberArray is declared as a property:
#property(nonatomic, retain) NSMutableArray* prjMemberArray;
If I use this
prjMemberArray = [[NSMutableArray alloc] initWithObjects:#"someone",#"someone",#"someone" ,nil];
with release called in viewDidUnload,
then when the view loaded , it will crashes immediately But when I use this:
prjMemberArray = [[NSMutableArray alloc] initWithCapacity:0];
[prjMemberArray addObject:#"someone"];
it works well. Can anyone explain this? I use a storyboard to present the current view controller, like this:
UIStoryboard* sb = [UIStoryboard storyboardWithName:#"MainStoryboard" bundle:nil];
prj_Detail = [sb instantiateViewControllerWithIdentifier:#"ProjectDetailVC"];
[self presentModalViewController:prj_Detail animated:YES];
Where prjMemberArray is a property of prj_Detail.
Are you sure you have not misspelled items and written e.g. "someone" instead of #"someone" in the crashing scenario?
Don't forget to use self when referring to properties. Here's the a safe way to declare that without having to worry about leaks:
Header:
#property(nonatomic, retain) NSMutableArray* prjMemberArray;
Implementation:
#synthesize prjMemberArray=_prjMemberArray;
- (void) viewDidLoad {
[super viewDidLoad];
NSMutableArray *prjMemberArray = [[NSMutableArray alloc] initWithObjects:#"someone", #"someone", #"someone" ,nil];
self.prjMemberArray = prjMemberArray;
[prjMemberArray release];
}
- (void) dealloc {
[_prjMemberArray release];
[super dealloc];
}
#property creates the getter and setter for your variable but is often confused for a variable itself. When they released XCode4 I believe they added the ability to set what you want the instance variable to be named by doing:
#synthesize prjMemberArray=_prjMemberArray;
Before XCode4 you simply did:
#synthesize prjMemberArray;
So what #property is doing behind the scenes is a little something like this:
-(NSMutableArray*) prjMemberArray {
return _prjMemberArray;
}
-(void) setPrjMemberArray:(NSMutableArray *) val {
if( _prjMemberArray != nil )
[prjMemberArray release];
_prjMemberArray = [val retain];
}
So don't think of #property as a variable itself and remember to always use self when referring to them. That should save you a lot of pain and a few memory leaks as well.
This is one segment of codes used in one of my project for managing one of my class instance:
#interface C: NSObject
{
NSMutableArray *myArr;
}
#property (nonatomic,retain) NSMutableArray *myArr;
//...
#end
#implementation C
#synthesize myArr;
//...
-(id)init
{
//...
myArr = [[NSMutableArray alloc] init];
//...
}
//version 1 of dealloc method
-(void)dealloc
{
//...
self.myArr = nil;
//...
}
//version 2 of dealloc method
-(void)dealloc
{
//...
[myArr release];
//...
}
here the version 1 dealloc method doesn't work and Xcode says something like "EXC_BAD_ACCESS..." and the app crashed.
if I modified the dealloc method as version 2, it works.
Does anybody have any idea why?
Thx in advance.
As Duncan said, the EXEC_BAD_ACCESS error means that the object doesn't exist anymore.
This is probably due to the fact that myArr is being released before the dealloc gets called.
To facilitate memory management and to keep track of reference counts, I like to make it clearer in the init methods, for example:
-(id)init
{
//...
NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity:0];
self.myArr = array;
[array release];
//...
}
By using the generated setter self.myArr = array; you are ensuring that the reference count is being delt with correctly, it will release the old value and retain the new one for you.
#MadhavanRP : if the property is a retained property:
#property(nonatomic, retain) NSMutableArray *myArr;
calling
self.myArr = nil
is exactely the same as calling
[myArr release];
myArr = nil;
Edit: #Sylvain beat me to it :)
This is OK even if it's bad idea/confusing to have same name for iVar and property. I removed the iVar declaration.
#interface C: NSObject
{}
#property (nonatomic,retain) NSMutableArray *myArr;
//...
#end
Generate your iVar using #synthetize.
#implementation C
#synthesize myArr = _myArr;
//...
Your init is all wrong. You are assigning the iVar without using the setter method.
-(id)init
{
//...
// You were doing
// _myArr = [[NSMutableArray alloc] init];
// You should do
NSMutableArray array = [[NSMutableArray alloc] init];
self.myArr = array;
[array release];
// You could avoid the temporary variable but this confuse XCode static analyzer
//...
}
This is OK. I guess that #synthetize generated another iVar to back your property.
This other iVar was not properly assign.
You would not notice this if you do not user self.myArr (or the equivalent [self myArr]).
This confusion is main reason why hardcore ObjC programmer do not like the new property thing. :) This confuse new programmers.
//version 1 of dealloc method
-(void)dealloc
{
//...
self.myArr = nil;
//...
}
This is not good as you bypass the setter, as in init method. This was working anyway.
//version 2 of dealloc method
-(void)dealloc
{
//...
[myArr release];
//...
}
It looks like your myArr object is being messaged when it should not be, in the first case you hide the problem by setting it to nil, in the second you don't. Either method should not crash. When do you call [super dealloc]; (you should call it at the end of the dealloc implementation).
I've started cleaning up my app before publication - using "Instruments" Leak analyzer.
I found a leak I can't plug. So I built a simple project to illustrate the problem. Please see code below. I put a button on the view to test fire the procedure "test". It always generates a leak.
First the header and code for an object named "theObj"
#import <Foundation/Foundation.h>
#interface theObj : NSObject {
NSString* theWord;
}
#property (nonatomic,retain) NSString* theWord;
#end
#import "theObj.h"
#implementation theObj
#synthesize theWord;
-(id) initWithObjects: (NSString *) aWord;
{
if (self = [super init]){
self.theWord = aWord;
}
return self;
}
-(void) dealloc{
[theWord release];
[super dealloc];
}
#end
Now the view controller
#import <UIKit/UIKit.h>
#import "theObj.h"
#interface LeakAnObjectViewController : UIViewController {
NSMutableArray* arrObjects;
}
- (IBAction)test;
#end
#import "LeakAnObjectViewController.h"
#implementation LeakAnObjectViewController
- (IBAction)test {
if (arrObjects == nil)
arrObjects = [[NSMutableArray alloc] init];
NSString* aStr = #"first";
[arrObjects addObject:[[theObj alloc] initWithObjects:aStr]];
[arrObjects removeAllObjects];
}
You alloc the object, which means you own it. Then you give it to the array, which means the array owns it as well. Then the array removes it, so you are the only owner. But you don't have a reference to the object anymore, so you can't release it, so it's just leaked.
Someone really needs to learn the rules around memory management. Specifically as it pertains to ownership, etc.