Question

Possible Duplicate:
Use autorelease when setting a retain property using dot syntax?

What is difference between using ivars and self. notation?

instanceVar is instance variable declared with retain.

1) instanceVar = [[NSMutableArray alloc] initWithObjects:@”1″, @”2″]; //do I need autorelease here?????

2) self.instanceVar = [[NSMutableArray alloc] initWithObjects:@”1″, @”2″] autorelease];

Also, Do I need autorelease in the first situation?

Answer 1

This is explained in multiple places but seems as you asked what the different is

The first call is unchanged and looks like this:

instanceVar = [[NSMutableArray alloc] initWithObjects:@"1", @"2"];

The second call when compiled will look something like this (assuming you have used a @property with retain and @synthesize:

self.instanceVar = [[NSMutableArray alloc] initWithObjects:@"1", @"2"];
// The previous line will compile to this next line
[self setInstanceVar:[[NSMutableArray alloc] initWithObjects:@"1", @"2"]];

The body of the - (void)setInstanceVar:(NSMutableArray *)instanceVar; method will look something like this (the compiler create this for you because of your @property and @sythesize):

- (void)setInstanceVar:(NSMutableArray *)anInstanceVar
{
    if (instanceVar != anInstanceVar) {
        [instanceVar release];
        instanceVar = [anInstanceVar retain];
    }
}

Therefore in the call

self.instanceVar = [[NSMutableArray alloc] initWithObjects:@"1", @"2"];

You have the +1 retain count on the newly created NSMutableArray and then you have the +1 retain count added from going through the setter.

This means that you require the extra release to match retains you are taking. It is considered better to not use autorelease in iPhone so you can be sure memory is being freed when you want it to. Therefore you should normally take the pattern

1. Create local var
2. Assign local var to ivar through setter
3. release local var

Which looks like this (FIXED thanks to @jamapag)

NSArray *tmpMyArray - [[NSArray alloc] initWithObject:@"Hello"];
self.myArray = tmpMyArray;
[tmpMyArray release]; tmpMyArray = nil;