Problem with releasing an object - objective-c

Question

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.)

Answer 1

+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];

Answer 2

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...

Answer 3

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.

Answer 4

I would also recommend changing:
if ([self object] != nil)
[[self object] release];
to:
[self setObject:nil];
It's less code and functionally equivalent. =)

Answer 5

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)];