Here is my custom class:
PolygonShape : NSObject {
int numberOfSides;
int minimumNumberOfSides;
int maximumNumberOfSides;
}
My custom init method:
- (id)initWithNumberOfSides:(int)sides minimumNumberOfSides:(int)min maximumNumberOfSides:(int)max {
if (self = [super init]) {
[self setMinimumNumberOfSides:min];
[self setMaximumNumberOfSides:max];
[self setNumberOfSides:sides];
}
return self;
}
My dealloc method:
- (void) dealloc {
NSLog("Calling dealloc");
[super dealloc];
}
My sample code that crashes:
PolygonShape *shape1 = [[PolygonShape alloc] initWithNumberOfSides:6 minimumNumberOfSides:5 maximumNumberOfSides:9];
[shape1 release];
I've alloc-ed a PolygonShape increasing the retain count by 1 and then release-ing should decrement it to 0 and call dealloc, printing that message to NSLog but I just get EXC_BAD_ACESS. I'm able to access and change the fields in my object after creating it so everything up until there works. Many thanks for the help!
NSLog("Calling dealloc");
You are passing a regular C string, rather than an NSString. You need to do this:
NSLog(#"Calling dealloc");
Your compiler should have warned you about passing an incompatible pointer.
Have you added these into the #interface...
#property(assign) int numberOfSides, minimumNumberOfSides, maximumNumberOfSides;
and these into the #implementation?
#synthesize numberOfSides, minimumNumberOfSides, maximumNumberOfSides;
The setters won't be generated automatically unless you explicitly #synthesize it.
What line does it crash on? Could the error be in one of the methods you call in initWithNumberOfSides?
If doing "build and debug" to find where it crashes doesn't help, I'd turn on NSZombieEnabled to find the problem (don't forget to switch it off again!)
Related
Here's a little example of using weak arguments:
#interface MYTestObject : NSObject
#end
#implementation MYTestObject {
void(^_block)(void);
}
- (void)dealloc {
NSLog(#"DEALLOC!");
}
- (id)init {
if (self = [super init]) {
[self doSomethingWithObject:self];
}
return self;
}
- (void)doSomethingWithObject:(id __weak /* <- weak argument! */)obj {
_block = ^{
NSLog(#"%p", obj);
};
}
#end
And it works: -dealloc is called!
Also, if you remove __weak you'll get a retain-cycle and it's absolutely correct.
Wonder, if that's just a side-effect and it's completely unsafe to use weak arguments? Or is it a specified behavior and I'm just a bad google-user?
Two observations:
I'd be inclined to make a local __weak reference within doSomethingWithObject, rather than make it a __weak argument as illustrated in Avoid Strong Reference Cycles when Capturing self.
I don't think that it is, as you asked, "completely unsafe to use weak arguments." But if nothing else, it's the more common pattern to have a local __weak variable and strikes me as more appropriate as an implementation detail of doSomethingWithObject rather than part of the method's public interface.
I'd also make block a property with the copy memory qualifier. As the docs say
You should specify copy as the property attribute, because a block needs to be copied to keep track of its captured state outside of the original scope. This isn’t something you need to worry about when using Automatic Reference Counting, as it will happen automatically, but it's best practice for the property attribute to show the resultant behavior.
Thus:
#interface MYTestObject : NSObject
#property (nonatomic, copy) void(^block)(void);
#end
#implementation MYTestObject
- (void)dealloc {
NSLog(#"DEALLOC!");
}
- (id)init {
if (self = [super init]) {
[self doSomethingWithObject:self];
}
return self;
}
- (void)doSomethingWithObject:(MYTestObject *)obj {
typeof(obj) __weak weakObj = obj;
self.block = ^{
NSLog(#"%p", weakObj);
};
}
#end
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.
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).
What's wrong with this? The NSMutableString returns (null).
.h:
NSMutableString *aMutableString;
...
#property (assign) NSMutableString *aMutableString;
.m:
#synthesize aMutableString;
- (void)aMethod {
[self setAMutableString:[[NSMutableString alloc] initWithString:#"message: "]];
if (someCondition) {
[[self aMutableString] appendString:#"woohoo"];
}
}
- (void)anotherMethod {
NSLog(#"%#", [self aMutableString]);
[[self aMutableString] release];
}
First of all, your code has a couple of problems. First, you should define your aMutableString #property as retain, not assign. assign is generally for primitive, non-object types, like ints, etc., and for some special cases of objects. You appear to want to take ownership of aMutableString in such a way that it persists after the event loop returns. In your posted code, you end up accomplishing that because of how you incorrectly set the aMutableString in the following line:
[self setAMutableString:[[NSMutableString alloc] initWithString:#"message: "]];
By creating an NSMutableString with alloc/init, you're creating a potential memory leak situation, though in your situation, it actually makes up for your defining the property as assign rather than retain.
Your second -anotherMethod is also potentially dangerous in that:
1) it releases an instance variable you defined as assign
2) after releasing it, it doesn't set it to nil. If you try to access that instance variable elsewhere in that class at a later point in time, you will likely get a crash because the pointer is no longer valid, if the instance variable has been dealloced.
So, the code should most likely look something like this:
.h
NSMutableString *aMutableString;
...
#property (retain) NSMutableString *aMutableString;
.m:
#synthesize aMutableString;
- (void)dealloc {
[aMutableString release];
[super dealloc];
}
- (void)aMethod {
[self setAMutableString:[NSMutableString stringWithString:#"message: "]];
if (someCondition) {
[aMutableString appendString:#"woohoo"];
}
}
- (void)anotherMethod {
NSLog(#"%#", aMutableString);
// the following is potentially unsafe!
// [[self aMutableString] release];
// it should be one of the following:
[aMutableString release]; aMutableString = nil;
// or
// [self setAMutableString:nil];
}
That said, without more information, it's a little hard to say what the problem is. I assume you mean the NSLog() call is printing (null)? If so, that means that aMutableString is still nil. Are you calling -aMethod before calling -anotherMethod?
If you want to make sure that aMutableString is initialized to an empty string, you could override -init:
- (id)init {
if ((self = [super init])) {
aMutableString = [[NSMutableString alloc] init];
}
return self;
}
Make sure you have #synthesize aMutableString; in your .m file
I've got this code:
Entry.h
#import <Foundation/Foundation.h>
#interface Entry : NSObject {
id object;
SEL function;
}
#property (retain) id object;
#property (assign) SEL function;
-(Entry*) initWithObject:(id)object selector:(SEL)function;
#end
Entry.m
#import "Entry.h"
#implementation Entry
#synthesize object;
#synthesize function;
-(Entry*) initWithObject:(id)obj selector:(SEL)sel {
self = [super init];
[self setObject:obj];
[self setFunction:sel];
return self;
}
-(void) dealloc {
[super dealloc];
if ([self object] != nil)
[[self object] release];
}
#end
And when I do this:
Entry *hej = [Entry alloc];
[hej release];
I get:
objc[2504]: FREED(id): message object sent to freed object=0xf5ecd0
Program received signal: “EXC_BAD_INSTRUCTION”.
What am I doing wrong?
(And this insert code thing at stack overflow doesnt work, unless I'm doing something wrong and you're not supposed to click "code sample" and then paste.)
+alloc only allocates memory. You need -init to actually create the object in that memory space. Since you are only allocating memory and not creating an object there, calling -release on a chunk of memory is giving you an error. Further, you want your [super dealloc] call to appear at the end of you -dealloc method. Change those two things and the following should work:
Entry *hej = [[Entry alloc] init];
[hej release];
there are two problems here:
1) you need to check that self = [super init] does not return nil. Typical usage would be to follow wrap your initialization code with the conditional:
if ((self = [super init]) != nil) {
// initialize the object...
}
2) but where you are getting stuck is on instantiating your object: you should do it like this:
Entry *hej = [[Entry alloc] initWithObject:myObj selector:mySelector];
(assuming that you want to go through the custom initializer you just defined...
else just use the default init method.) but 'alloc' must be followed by an init.
Entry *hej = [[Entry alloc] init]; // will do the trick...
Firstly, you need an init to go with your alloc. Second, in dealloc, you send a message to self after calling [super dealloc]. You can't do that. The final deallocation should go at the end.
I would also recommend changing:
if ([self object] != nil)
[[self object] release];
to:
[self setObject:nil];
It's less code and functionally equivalent. =)
There are many things wrong with your code. I'll try to go through them.
First, its better to use a different ivar name to your property name so its clear where you are using each. Apple normally uses an underscore prefix, but any prefix will do.
#interface Entry : NSObject {
id _object;
SEL _function;
}
#property (retain) id object;
#property (assign) SEL function;
#synthesize object = _object;
#synthesize function = _function;
Next, you aren't using the standard init template (although this probably wont make any difference normally).
-(Entry*) initWithObject:(id)obj selector:(SEL)sel {
self = [super init];
if (self != nil) {
// initializations
}
return self;
}
Next, Apple (for good reasons) recommends against using getters/setters in your init/dealloc. So your init would be:
-(Entry*) initWithObject:(id)obj selector:(SEL)sel {
self = [super init];
if (self != nil) {
_object = [obj retain];
_object = sel;
}
return self;
}
Next, after [super dealloc] your object is destroyed, so you cannot reference self (and hence your ivars) after that, so your dealloc should look like:
-(void) dealloc {
// your deallocations
[super dealloc];
}
Further, as above, Apple recommends you should not use setters or getters in your dealloc routine, so your deallocation would initially look like:
if (_object != nil)
[_object release];
But further still, Objective C allows (and Cocoa encourages) that sending a method to nil does nothing. This is in stark contast to most other languages where messaging nil would cause a crash, but it is how Objective C/Cocoa work and you need to get used to it. So your deallocation is actually just:
[_object release];
And finally, alloc only allocates the memory for your object, you have to initialize it, so the initialization would be something like:
Entry *hej = [[Entry alloc] initWithObject:myobj selector:#selector(mymethod)];