Init class as subclass - objective-c

Question

My question is kind of weird, lets say I have a class inheriting from UITableViewCell called GenericTableViewCell and some more classes inheriting from GenericTableViewCell.
I want to be able to pass an argument to the GenericTableViewCell init method that will tell me which subclass of GenericTableViewCell should init this TableViewCell as.
Heres what I thought of but I know that it will fail because it has a recursive loop in it.
#implementation GenericTableViewCell
- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier cellIdentifier: (CellIdentifier *) identifier
{
self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
if (self) {
if ([identifier class] == [FirstIdentifier class]){
self = [[FirstTableViewCell alloc] initWithStyle:style reuseIdentifier:reuseIdentifier];
}
/// more else statements to check for other identifier cases
}
return self;
}
#end
Is there any way to do this? Or should I just check the identifier outside of the init function and by that decide which cell do I declare?

Answer 1

Yes, you can do this. It's a pattern you sometimes come across called a class cluster. If you are not using ARC, you must release the original value of self to stop a memory leak.
However, I would not do this. I would create a factory method in GenericTableViewCell.
+(GenericTableViewCell*) cellWithStyle: (UITableViewCellStyle)style
reuseIdentifier: (NSString *)reuseIdentifier
cellIdentifier: (CellIdentifier *) identifier
{
GenericTableViewCell* ret = nil;
if ([identifier class] == [FirstIdentifier class])
{
ret = [[FirstTableViewCell alloc] initWithStyle:style reuseIdentifier:reuseIdentifier];
}
else
{
// ....
}
return [ret autorelease];
}
You can eliminate the if statement by adding a method to CellIdentifier and overriding it in subclasseslike this:
// in CellIdentifier.m
-(id) classForCell
{
return [GenericTableViewCell class];
}
// in FirstIdentifier.m
-(id) classForCell
{
return [FirstTableViewCell class];
}
Then your factory method becomes
+(GenericTableViewCell*) cellWithStyle: (UITableViewCellStyle)style
reuseIdentifier: (NSString *)reuseIdentifier
cellIdentifier: (CellIdentifier *) identifier
{
return [[[[identifier classForCell] alloc] initWithStyle:style
reuseIdentifier:reuseIdentifier] autorelease];
}

Answer 2

The thing you should implement is called class cluster pattern. In your situation you shouldn't call initWithStyle:reuseIdentifier: on a subclass rather than in subclass' initializer:
In GenericTableViewCell:
- (id)initWithCustomIdentifier:(NSString *identifier) {
Class cellClass = NSClassFromString(identifier);
if (!cellClass) {
cellClass = [MyStandardTableViewCell class];
}
self = [[cellClass alloc] init];
return self;
}
In MyStandardTableViewCell (or any other subclass of GenericTableViewCell:
- (id)init {
self = [super initWithStyle:someStyle reuseIdentifier:NSStringFromClass([self class])];
if (!self) return nil;
// do extra setup here
return self;
}