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.
Related
I am trying to pass data between the viewcontrollers of a uitabbarcontroller using a singleton class as below:
#import <Foundation/Foundation.h>
#interface AppSingleton : NSObject {
NSMutableString *selectedStr;
}
#property(nonatomic,retain) NSMutableString *selectedStr;
+(AppSingleton*) sharedAppInstance;
#end
Here is my implementation file:
#import "AppSingleton.h"
#implementation AppSingleton
#synthesize selectedStr;
+(AppSingleton*) sharedAppInstance{
static AppSingleton *sharedAppInstance;
#synchronized(self){
if(!sharedAppInstance){
sharedAppInstance = [[AppSingleton alloc] init];
}
}
return sharedAppInstance;
}
-(void)dealloc{
[selectedStr release];
[super dealloc];
}
#end
I try to set the selectedStr in one of my viewcontrollers as below and print it in the NSLog however I get a null:
AppSingleton *sharedAppInstance;//in the header
sharedAppInstance = [AppSingleton sharedAppInstance];//in viewdidload
[sharedAppInstance setSelectedStr:self.someStr];
NSLog(#"selectedStr is: %#", sharedAppInstance.selectedStr);
When I debug this, the sharedAppInstance.selectedStr seems to be out of scope.
I would like to know where I am making a mistake.
Thank you.
I changed the placing of the setting/getting of my variable within the viewcontroller and it worked..
[sharedAppInstance setSelectedStr:self.someStr];
NSLog(#"selectedStr is: %#", sharedAppInstance.selectedStr);
I am trying to pass the selected object in my coredata from the rootviewcontroller to the edit view. The selected object is being passed but is then becoming null after the theObject=selectedObject is being called. Anyone know what im doing wrong?
This is in the edit.h
#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
#import "LearningAppDelegate.h"
#interface edit : UIViewController <UITextViewDelegate, UITableViewDelegate, UITableViewDataSource, UIActionSheetDelegate>{
UITableView *tableView;
NSManagedObject *theObject;
UITextView *messageView;
}
#property(nonatomic, retain) IBOutlet UITableView *tableView;
#property(nonatomic, retain) IBOutlet UITextView *messageView;
#property(nonatomic, retain) NSManagedObject *theObject;
-(id)initWithObject:(NSManagedObject *)selectedObject;
#end
This is in the edit.m:
-(id)initWithObject:(NSManagedObject *)selectedObject {
self = [super init];
if (nil == self) {
return nil;
}
NSLog(#"selectedObject: %#", selectedObject);
NSLog(#"selecetedObject.message: %#", [[selectedObject valueForKey:#"message"] description]);
theObject=selectedObject;
NSLog(#"theObject 1: %#", theObject);
NSLog(#"theObject.message 1: %#", [[theObject valueForKey:#"message"] description]);
return self;
}
// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
NSLog(#"theObject 2: %#", theObject);
NSLog(#"theObject.message 2: %#", [[theObject valueForKey:#"message"] description]);
messageView.text=[[theObject valueForKey:#"message"] description];
[super viewDidLoad];
}
I am actually amazed that doesn't crash for you. You're assigning the variable selectedObject into the instance variable theObject without retaining it for your own use. By accessing the instance variable directly in the assignment 'theObject=selectedObject', you're bypassing the behavior granted by the #property declaration. This means that once selectedObject is finally dealloc'd, theObject will point to garbage memory.
The correct way to do this is to put theObject = [selectedObject retain]; in the -initWithObject: method and in -viewDidLoad to access it via self.theObject rather than just theObject.
In my own usage I prefer to give instance variables names different from the actual property name to avoid confusion. For example:
#interface SomeClass : NSObject
{
#private
NSManagedObject *_theObject;
}
#property (nonatomic, retain) NSManagedObject *theObject;
...
#end
#implementation SomeClass
#synthesize theObject = _theObject
...
- (void)dealloc
{
[_theObject release], _theObject = nil;
[super dealloc];
}
#end
I only have experience with Coredata on the desktop, but the problem looks like it would be with your initWithObject method. At no point do you actually insert the new object into the managed object context. You should be using this method to make new objects:
- (id)initWithEntity:(NSEntityDescription *)entity insertIntoManagedObjectContext:(NSManagedObjectContext *)context
As an example in pseudocode:
NSManagedObject *newObject = [[NSManagedObject alloc] initWithEntity:NSENTITYDESCRIPTION insertIntoManagedObjectContext:MANAGEDOBJECTCONTEXT];
[newObject setValue:#"VALUE_OF_SELECTED_OBJECT" forKey:#"APPROPRIATE_KEY"];
//REPEAT AS NECESSARY
[MANAGEDOBJECTCONTEXT save];
*Code not tested, naming conventions are ignored, etc.
The save is important. If you don't do this the object won't persist.
If I have a custom class called Tires:
#import <Foundation/Foundation.h>
#interface Tires : NSObject {
#private
NSString *brand;
int size;
}
#property (nonatomic,copy) NSString *brand;
#property int size;
- (id)init;
- (void)dealloc;
#end
=============================================
#import "Tires.h"
#implementation Tires
#synthesize brand, size;
- (id)init {
if (self = [super init]) {
[self setBrand:[[NSString alloc] initWithString:#""]];
[self setSize:0];
}
return self;
}
- (void)dealloc {
[super dealloc];
[brand release];
}
#end
And I synthesize a setter and getter in my View Controller:
#import <UIKit/UIKit.h>
#import "Tires.h"
#interface testViewController : UIViewController {
Tires *frontLeft, *frontRight, *backleft, *backRight;
}
#property (nonatomic,copy) Tires *frontLeft, *frontRight, *backleft, *backRight;
#end
====================================
#import "testViewController.h"
#implementation testViewController
#synthesize frontLeft, frontRight, backleft, backRight;
- (void)viewDidLoad {
[super viewDidLoad];
[self setFrontLeft:[[Tires alloc] init]];
}
- (void)dealloc {
[super dealloc];
}
#end
It dies after [self setFrontLeft:[[Tires alloc] init]] comes back. It compiles just fine and when I run the debugger it actually gets all the way through the init method on Tires, but once it comes back it just dies and the view never appears. However if I change the viewDidLoad method to:
- (void)viewDidLoad {
[super viewDidLoad];
frontLeft = [[Tires alloc] init];
}
It works just fine. I could just ditch the setter and access the frontLeft variable directly, but I was under the impression I should use setters and getters as much as possible and logically it seems like the setFrontLeft method should work.
This brings up an additional question that my coworkers keep asking in these regards (we are all new to Objective-C); why use a setter and getter at all if you are in the same class as those setters and getters.
You have declared frontLeft as a 'copy' property:
#property (nonatomic,copy) Tires *frontLeft, *frontRight, *backleft, *backRight;
When you assign to this property, a copy is made by invoking the object's copy method. This only works for objects which support the NSCopying protocol (i.e., which implement a copyWithZone: method). Since your Tires class does not implement this method, you get an exception.
You probably want to change this to be a 'retain' property:
#property (nonatomic,retain) Tires *frontLeft, *frontRight, *backleft, *backRight;
See the Objective C documentation on declared properties for more on property declarations.
One problem that i see is here:
- (void)viewDidLoad {
[super viewDidLoad];
[self setFrontLeft:[[Tires alloc] init]];
}
When you call [Tires alloc] you get back an object with a retain count of 1. You then use a set method which you have synthesized, which bumps the retain count to 2. When your object is done with the Tire object, it will reduce the retain count back to 1, but the tire will never get deallocated. I think you should use:
[self setFrontLeft:[[[Tires alloc] init] autorelease]];
Having some issues with code not executing within the classes I created and thought I initialized and implemented correctly here are all the files. There is a class with an array of another class. Then implemented in the code finally but for some reason none of the NSLog calls seem to execute except the one immediately before [mobdefs createTable] in the main code. All help appreciated...
// Mobdefs.h
#interface Mobdefs : NSObject {
#public NSMutableArray *mobInfo;
}
#property(retain) NSMutableArray *mobInfo;
-(void) createTable;
#end
// Mobdefs.m
#import "Mobdefs.h"
#import "Mobrec.h"
#implementation Mobdefs
#synthesize mobInfo;
- (id) init
{
mobInfo = [[NSMutableArray alloc] init];
return self;
}
-(void) addmobrec
{
MobRec *aNewMobRec = [[MobRec alloc] init];
aNewMobRec.mName=#"newbie";
[mobInfo addObject:aNewMobRec];
[aNewMobRec release];
NSLog(#"MobRec Added\n");
}
-(void) createTable
{
NSLog(#"Populating mob table.\n"); // *** THIS CODE NEVER SEEMS TO GET EXECUTED
}
#end
//main.h
Mobdefs *mobdef;
//main.m
NSLog(#"just before createTable call\n");
[mobdef createTable];
although the createTable code is called in the main the only NSLog output I get is the 'just before createtable...'
It doesn't seem that you have initialized mobdef. Add the following:
mobdef = [[Mobdefs alloc] init];
to your main.m before you invoke the method on it.
Objective-C silently ignore calls on nil, as mobdef would be initialized to initially.
are you allocating and initializing mobdef in main.m?
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.