NSCopying & Inheritance

Question

Hi,

Please have a look on following code :------- .h

@interface BankAccount : NSObject<NSCopying>
{
    double accountBalance;
    long accountNumber;
    NSString *CustomerName;
    NSString *AccountType;
}

-(void) setAccount: (long) y andBalance: (double) x;
-(void) setCustomerName: (NSString*) name andAccountType: (NSString*) type;
-(id)copyWithZone:(NSZone *)zone;

@end

@interface Savings : BankAccount
{
    int number;
    NSString *Offer;
}
-(void) setSavingNumber: (uint8_t) num andOffer: (NSString*) offer;
-(id)copyWithZone:(NSZone *)zone;
@end

---------- .m

@implementation BankAccount

-(void) setAccount: (long) y andBalance: (double) x
{
    accountNumber = y;
    accountBalance = x;
}
-(void) setCustomerName: (NSString*) name andAccountType: (NSString*) type
{
    CustomerName = name;
    AccountType = type;
}

-(id)copyWithZone:(NSZone *)zone
{
    BankAccount *accountCopy = [[BankAccount allocWithZone: zone] init];
    [accountCopy setAccount: accountNumber andBalance: accountBalance];
    [accountCopy setCustomerName:CustomerName andAccountType:AccountType];
    return accountCopy;
}

@end

@implementation Savings
-(void) setSavingNumber: (uint8_t) num andOffer: (NSString*) offer
{
    number = num;
    Offer = offer;
}

-(id)copyWithZone:(NSZone *)zone
{
    Savings * clone = [super copyWithZone:zone];
    [clone setSavingNumber:number andOffer:Offer];************** error *********
    return clone;
}

@end

When run this code::::::

Savings* account1;
Savings* account2;

account1 = [[Savings alloc] init];
[account1 setAccount:10 andBalance:1000.10];
[account1 setCustomerName:[NSString stringWithFormat:@"%@",@"Deepak"] andAccountType:[NSString stringWithFormat:@"%@",@"Savings"]];
[account1 setSavingNumber:2001 andOffer:@"Bad"];    
account2 = [account1 copy];

#

i dont know what is wrong with the code please help me. thanks in advance.

Thanks Deepak

Answer 1

Ok first, your test code is bad because you set a saving number of 2001 in an 8 bit integer. Second, your code does not run because you're trying to call setSavingNumber:andOffer: on a BankAccount instead of an Saving object so it can't find the selector for this method at run time. Thanks David for pointing that out.

When implementing BankAccount::copyWithZone, you used the alloc-init and you returned the object which is fine. When implementing Savings::copyWithZone, you call super copyWithZone. What you get is an object of type BankAccount so you cannot use setSavingNumber:andOffer: on it. Since you used the alloc-init in the base class, you should also use the alloc-init and setMethods in the Savings class.

To avoid duplicating code, I'd recomment implementing an initWithBankAccount in BankAccount and the same in Savings.

Then in the copyWithZone, you'd have

return [[BankAccount allocWithZone:zone] initWithBankAccount:self];

and

return [[Savings allocWithZone:zone] initWithSavings:self];

Although you must make sure that in initWithSavings you call either

self = [super initWithBankAccount:savings];

or you call straight init and you copy the base member initialization.

Have a look at Implementing object copy from Memory management programming guide.