What is the difference of using:
+ (id) myMethod;
// Rather than
- (id) myMethod;
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possible duplicate of [What do the plus and minus signs mean in Objective C next to a method?](http://stackoverflow.com/questions/2097294/what-do-the-plus-and-minus-signs-mean-in-objective-c-next-to-a-method) – vikingosegundo Jun 30 '12 at 16:16
3 Answers
1
Using a + declares the method as a class method, or a method that can be called directly on the class, where the class is the object. So when you have this:
@implementation Foo
+(NSString*)method1 {
return @"Foo";
}
-(NSString*)method2 {
return @"Foo";
}
@end
The methods are called in different ways:
[Foo method1]; //=> @"Foo"
Foo* f=[[Foo alloc] init];
[f method2]; //=> @"Foo"
One other thing to note is that class methods don't have access to an instance, which means they can't access any kind of instance variables.
Linuxios
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1… and, therefore, class methods are not getters. They're just class methods. Also, your example would be clearer if the two methods returned different values. – Ken Thomases Jun 30 '12 at 14:39
1
@Linuxios pretty much summed up the concept of class and instance method. However, since you mentioned getters and setters in your title, I want to point out that in Objective-C you can use properties instead of writing your own accessor methods. For example,
In the header file, you will have something like this:
@interface MyObject : NSObject
@property (nonatomic,retain) NSSet* mySet;
@end
In the m file, you wil have something like this:
@implement MyObject
@synthesize mySet;
@end
To access the set in another class you can do it like this:
myObject.mySet; // assuming myObject is an instance of the MyObject class
Jennifer Wong
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The top one is a class method (no instance required) The second one is a instance variable (attached to a specific instance).
This answer explains the methods quite well:
[MyObject myMethod]; // did not have to create an instance
MyObject* myNewObject = [[MyObject alloc] init] autorelease];
[myNewObject myMethod]; // had to create an instance
