CODEWITHSUNDEEP
iphoneobjective-cxcodeipad
Andrew
Andrew

Reputation: 3999

Override @synthesize method?

I have one class called dog and another class called cat.

Dog has an variable, "name" declared with @property in the .h file.

In the cat class, I have set the name by using the command, myDog.name = "buster", after creating the variable "myDog" of type dog.

I would like to do additional operations when the name is set by overriding the set method normally created by the @synthesize command.

How can I do that? Thanks for the help!

Upvotes: 1

Views: 5433

Answers (3)

Regexident
Regexident

Reputation: 29552

You cannot override (and call it within) a synthesized method from within the very same class.

You can however override it from a subclass (or rather: synthesize it in an abstract superclass).

If you simply want to perform additional (vs. different) operations upon property change I would use KVO by simply adding each dog as observer to its own "name" property in -(id)init;.

Edit:

There is a way to add additional logic to synthesized methods from within the same class:
Define a private intermediate property in a class extension.

I've attached source code for a class which uses synthesized properties and takes care(sic!) of keeping the dog's owner in sync with its own identity.

Dog.h:

#import <Foundation/Foundation.h>

@interface Dog : NSObject {
@private
    NSString *name;
    NSString *owner;
}

@property (nonatomic, readwrite, retain) NSString *name;
@property (nonatomic, readwrite, retain) NSString *owner;

@end

Dog.m:

#import "Dog.h"

@interface Dog ()

@property (nonatomic, readwrite, retain) NSString *primitiveName;

@end

@implementation Dog

@dynamic name;

@synthesize primitiveName = name;
@synthesize owner;

- (id)init {
    if ((self = [super init])) {
        name = @"Snowy";
        owner = @"Tintin";
    }

    return self;
}

- (void)dealloc {
    [super dealloc];
}

- (NSString *)name {
    return self.primitiveName;
}

- (void)setName:(NSString *)aName {
    self.primitiveName = aName;
    if ([aName isEqualToString:@"Snoopy"]) {
        self.owner = @"Charlie Brown";
    }
    else if ([aName isEqualToString:@"Snowy"]) {
        self.owner = @"Tintin";
    }
}

- (NSString *)description {
    return [NSString stringWithFormat:@"<%@ name:'%@' owner:'%@'>", [self class], self.name, self.owner];
}

@end

Test:

Dog *dog = [[Dog alloc] init];
NSLog(@"%@", dog);
dog.name = @"Snoopy";
NSLog(@"%@", dog);
dog.name = @"Snowy";
NSLog(@"%@", dog);

Result:

<Dog name:'Snowy' owner:'Tintin'>
<Dog name:'Snoopy' owner:'Charlie Brown'>
<Dog name:'Snowy' owner:'Tintin'>

Upvotes: 1

Perception
Perception

Reputation: 80603

This has been pretty much answered on SO already - see Objective-C synthesize property name overriding for details. In particular, @Dev Kanchen's answer which includes example code.

Upvotes: 3

Chance Hudson
Chance Hudson

Reputation: 2859

All you have to do is leave the @synthesize then create whichever methods you want to be custom. Example:

In .h

@property(nonatomic, retain)NSString *Bob;

In .m

@synthesize bob;

-(void)setBob:(NSString *)bobValue{
    [bobValue retain];
    [bob release];
    bob = bobValue;
    //your custom stuffs here
}

Upvotes: 5

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