Inititating a variable with properties self vs. non self

Question

I have properties for my variables (all on retain) - the problem is, that if i am initiating it without self, my app is crashing. As mentioned in the docs, I should not init my variables with self.variable = but with variable =
so, where is the difference and why is my app crashing?
not crashing:
- (id)initWithNibName:(NSString *)nibName bundle:(NSBundle *)nibBundle {
self = [super initWithNibName:nibName bundle:nibBundle ];
if (self)
groupDict = [NSDictionary dictionaryWithObjectsAndKeys:
@"true", HAS_AGE,
@"true", HAS_GENDER,
@"true", HAS_EMOTION,
@"true", HAS_RELATIONSHIP,
@"true", HAS_WEALTH,
@"true", @"hasLanguages",
nil];
groupKeyArray = [groupDict allKeys];
setableAttributeKeyArray = [NSArray arrayWithObjects: HAS_RELATIONSHIP,
HAS_AGE, HAS_GENDER, HAS_EMOTION, HAS_WEALTH, HAS_LANGUAGE, nil];
[self getAttributeKeys];
prefs = [NSUserDefaults standardUserDefaults];
isTextUsed = TRUE;
[self loadUserProfile];
return self;
crashing:
- (id)initWithNibName:(NSString *)nibName bundle:(NSBundle *)nibBundle {
self = [super initWithNibName:nibName bundle:nibBundle ];
if (self)
groupDict = [NSDictionary dictionaryWithObjectsAndKeys:
@"true", HAS_AGE,
@"true", HAS_GENDER,
@"true", HAS_EMOTION,
@"true", HAS_RELATIONSHIP,
@"true", HAS_WEALTH,
@"true", @"hasLanguages",
nil];
groupKeyArray = [groupDict allKeys];
setableAttributeKeyArray = [NSArray arrayWithObjects: HAS_RELATIONSHIP,
HAS_AGE, HAS_GENDER, HAS_EMOTION, HAS_WEALTH, HAS_LANGUAGE, nil];
[self getAttributeKeys];
prefs = [NSUserDefaults standardUserDefaults];
isTextUsed = TRUE;
[self loadUserProfile];
return self;
interestingly, I have found out that the crash only depends on my groupDict variable.
crash:
groupDict = [NSDictionary dictionaryWithObjectsAndKeys: blabla
no crash:
self.groupDict = [NSDictionary dictionaryWithObjectsAndKeys: blabla

Answer 1

Hi Alex -
sommeralex wrote:
so, where is the difference and why is my app crashing?
@interface MyClass : NSObject {
NSString *foo;
@property (nonatomic, retain) NSString *foo;
- (IBAction)doSomething:(id)sender;
@end
@implementation MyClass
@synthesize foo;
- dealloc {
[foo release];
[super dealloc];
- (IBAction)doSomething:(id)sender {
UIButton *button = sender;
NSString *string = [NSString stringWithFormat:@"Button %d was pressed", button.tag];
// Line 1 simply stores the address of the NSString instance in the ivar named foo:
foo = string; // Line 1
// Line 2 also stores the string address in the foo ivar, but does something else as well:
self.foo = string; // Line 2
// Line 2 is exactly equivalent to Line 3:
[self setFoo:string]; // Line 3
setFoo is the "setter" for the ivar foo which was declared by the @property directive and automatically implemented because of the @synthesize directive. Since the @property directive included the "retain" attribute, setFoo will retain the string object. Note that 'string' was created by a NSString convenience method which means it has been autoreleased. So if we use Line 1 to store the pointer to that NSString instance, the object will soon be deallocated, and if we try to use foo after that, we will crash. But either Line2 or Line3 will retain the NSString object, so it won't be released until another object's pointer is stored in foo, or the parent object is deallocated.
Everything in the foo example applies to your groupDict ivar (assuming you declared a retaining property named groupDict). The object pointed to by groupDict was created by dictionaryWithObjectsAndKeys, which is a convenience method. So unless the setter (setGroupDict) is used, the address stored in groupDict will become invalid at the end of the current event cycle, and any attempt to use groupDict after that will crash.
As mentioned in the docs, I should not init my variables with self.variable = but with variable =
Can you point us to the doc that says that? I might've missed that Obj-C lesson, but up till now I've never heard of a reason not to call setter methods from an init method, provided you've executed [super init] first, and provided you aren't calling a custom setter method which requires the existence of another object. In any case, you could always take the code you posted out of init and put it in awakeFromNib or viewDidLoad.
- Ray