Useful Objective-C Snippets

createDocumentSubdir.m

// Create a path to a directory, and make sure it exists.
// The iOS documentation will tell you that URLs are preferred, but there is no createDirectory method for 
// URLs.  So we have to use string paths instead.

// Create a sub-directory in the application's Documents directory.  Return the path on success, or nil on failure.
- (void)createDocumentSubdirectory:(NSString*)dirName {
	NSString *retval = nil;
	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
	NSString *dirPath = [[paths objectAtIndex:0] stringByAppendingPathComponent:dirName];
	NSFileManager *fm = [[NSFileManager alloc] init];

	if (dirPath && fm) {
		if ([fm createDirectoryAtPath:dirPath withIntermediateDirectories:YES attributes:nil error:nil])
			retval = dirPath;
	}

	if (fm)
		[fm release];

	return retval;
}

simplePredicate.m

// A very simple predicate example, that allows you to remove items from an array that match some criteria
// In this case, we want to remove everything with a given uuid

NSPredicate *pred = [NSPredicate predicateWithFormat:@"uuid == %@", uuid];
NSArray *removableThings = [self.targetArray filteredArrayUsingPredicate:pred];
		
[self.targetArray removeObjectsInArray:removableThings];
		

typeTesting.m

// This is borrowed from my character sheet program.
// Assume we have a FateCharacter class...

id character = [NSKeyedUnarchiver unarchiveObjectWithFile:oneFullPath];
if ([character isKindOfClass:[FateCharacter class]])
    [self.characterArray addObject:character];