Create subclass with different subclass property
cocoa, objective-c, subclass
Solution
You can make it work, by using different backing variables, when synthesizing it looks like this: `@synthesize nicestArrayEver = nicestArrayEverSubClass_;`
#import <Foundation/Foundation.h>
@interface CustomClass : NSObject
@property (nonatomic, strong) NSArray * nicestArrayEver;
@end
@implementation CustomClass
@synthesize nicestArrayEver ;
-(id)init
{
if (self = [super init]) {
nicestArrayEver = [[NSArray alloc] init];
}
return self;
}
@end
@interface ASubClassCustomClass : CustomClass
@property (nonatomic, strong) NSMutableArray * nicestArrayEver;
@end
@implementation ASubClassCustomClass
@synthesize nicestArrayEver = nicestArrayEverSubClass_;
-(id)init{
if (self = [super init]) {
nicestArrayEverSubClass_ = [[NSMutableArray alloc] init];
}
return self;
}
@end
int main(int argc, const char * argv[])
{
@autoreleasepool {
CustomClass *c1 = [[[CustomClass alloc] init] autorelease];
ASubClassCustomClass *c2 = [[[ASubClassCustomClass alloc] init] autorelease];
NSLog(@"%@", NSStringFromClass([[c1 nicestArrayEver] class]));
NSLog(@"%@", NSStringFromClass([[c2 nicestArrayEver] class]));
}
return 0;
}
output
2012-05-27 01:59:16.221 NicestArray[2312:403] __NSArrayI
2012-05-27 01:59:16.225 NicestArray[2312:403] __NSArrayM
Another approach could be to have 2 init methods in the base class, one, that will instantiate the property and one, that won't, but leaves that task for the child class — this will prevent you from creating expensive objects just to throw them away. Now the base class could get instantiated directly with the second init and go to a false state. You can avoid this by checking the self class type with `isMemberOfClass:`, and throw an error, if the class type is the base class.
@interface CustomClass : NSObject
@property (nonatomic, strong) NSArray * nicestArrayEver;
-(id)initWithoutArray;
@end
@implementation CustomClass
@synthesize nicestArrayEver ;
-(id) initWithoutArray
{
if (self = [super init]) {
if ([self isMemberOfClass:[CustomClass class]]) {
[NSException raise:@"AbstractMethodCall" format:@"%@ should be called only from Subclasses of %@", NSStringFromSelector(_cmd), NSStringFromClass([self class])];
}
}
return self;
}
-(id)init
{
if (self = [super init]) {
nicestArrayEver = [[NSArray alloc] init];
}
return self;
}
@end
@interface ASubClassCustomClass : CustomClass
@property (nonatomic, strong) NSMutableArray * nicestArrayEver;
@end
@implementation ASubClassCustomClass
@synthesize nicestArrayEver = nicestArrayEverSubClass_;
-(id)init{
if (self = [super initWithoutArray]) {
nicestArrayEverSubClass_ = [[NSMutableArray alloc] init];
}
return self;
}
@end
int main(int argc, const char * argv[])
{
@autoreleasepool {
CustomClass *c1 = [[[CustomClass alloc] init] autorelease];
ASubClassCustomClass *c2 = [[[ASubClassCustomClass alloc] init] autorelease];
NSLog(@"%@", NSStringFromClass([[c1 nicestArrayEver] class]));
NSLog(@"%@", NSStringFromClass([[c2 nicestArrayEver] class]));
//this works, as it is the subclass
ASubClassCustomClass *shouldWork = [[[ASubClassCustomClass alloc] init] autorelease];
// ouch!
CustomClass *shouldCrash = [[[CustomClass alloc] initWithoutArray] autorelease];
}
return 0;
}
Problem
Say I have this Class ``` @interface CustomClass : NSObject @property (nonatomic, strong) NSArray * nicestArrayEver; @end ``` And I want to create a subClass of CustomClass, but here is the catch ``` @interface ASubClassCustomClass : CustomClass @property (nonatomic, strong) NSMutableArray * nicestArrayEver; @end ``` The issue as you can imagine is that when I initialize ASubClassCustomClass and call it's super initializer (since there is other properties required) the inmutable nicestArrayEver is created.. how can I avoid it's creation so I can set the mutable one? Note: This is just an example, the real implementation calls a heavy to create and really customized subclass (is not an NSArray).