autorelease pools and release/retain

in general, if you use the [ [object alloc] init] method of creating an object in memory, it is up to you to release it

if you use any other method to create the object, such as a class method (+), it is generally configured to be autoreleased

you can have multiple autorelease pools, including nested pools

cocoa gives you an autorelease pool for every program, but a foundation only program does not

it is generally good practice to use an autorelease pool in each method that needs one

make sure to distinguish that you are actually creating objects, rather than simply getting a reference to an object in a particular method

example:

...
	NSAutoreleasePool *aPool = [[NSAutoreleasePool alloc] init];
 
	NSArray *filenames = [fm directoryContentsAtPath:path];
	NSMutableArray *fullFilenames = [[NSMutableArray alloc] initWithCapacity:[filenames count]];
	int i;
	for(i=0; i<[filenames count]; i++){
		NSString *fullPath = [NSString stringWithFormat:@"%@/%@", path, [filenames objectAtIndex:i]];
		[fullFilenames addObject:fullPath];
		// fullPath is 2, and will be released to 1 after removeAllObjects,
		// then autoreleased to 0 if not retained elsewhere
	}
 
	[gridView createGridItemViews:fullFilenames];
 
	[fullFilenames removeAllObjects];
	[fullFilenames release];
 
	// the following method call releases the "filenames" array, and the "fullPath" objects
	[aPool release];
 
...

objects have a retainCount, and when it reaches zero the object is deallocated from memory

to find the retainCount you send the message to the object: (int)[object retainCount]

to increment the retainCount, you send the message: [object retain]

to decrement the retainCount, you send the message: [object release]

adding an object to a mutable array increases the retain count by 1

removing an object from a mutable array decreases the retain count by 1

adding a view to another view (subview/superview) increases the retain count by 1

removing or replacing a subview with another view decreases the retain count by 1

if you need to keep an object around, you may need to use [object retain] before some of the methods that decrement the retain count