Use of @synthesize/@property in Objective-C inheritance

Question

If you have Class A with an instance var "foo" which has a @property/@synthesize directive, and Class B inherits from Class A, does it also need to @property/@synthesize "foo"? The reason I ask is because when I try to use Class B's "foo", the calling class says that "foo" is not something of a structured union or a member, which makes me believe it needs to be explicitly synthesized.

Solution 1

No, you don't. Synthesized properties are added to class A and its subclasses automatically.

Solution 2

If you have Class A with an instance var "foo" which has a @property/@synthesize directive, and Class B inherits from Class A, does it also need to @property/@synthesize "foo"?

No.

The reason I ask is because when I try to use Class B's "foo", the calling class says …

No, the compiler says it.

… that "foo" is not something of a structured union or a member, which makes me believe it needs to be explicitly synthesized.

It is. In class A.

The compiler is giving you that warning because it doesn't know about the @property, which is because you have neither declared it nor imported a header that declares it. You say that class A's header declares the property, so import class A's header into class B's implementation, so that the compiler knows about the property when compiling class B.

Solution 3

Just in case this helps someone.

I came across this problem too and read these answers and still couldn't access super class variables directly. They were declared as properties and synthesized in the super class and and I had imported the header into my subclass. I was stuck until I discovered I needed to declare the member variables in the @interface section in the super class as well as a property of the superclass....! e.g.

@interface BuoyAnnotation : NSObject <MKAnnotation>
{
    CLLocationCoordinate2D coordinate;
    CLLocation* location;
    int type; 

}

@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;
@property (nonatomic, retain) CLLocation* location;
@property (nonatomic, assign) int type;

Solution 4

WHen inheriting you should not need to redeclare any properties or variables.

Perhaps if you post your ClassB header file or a portion of then people can better pinpoint your problem.

View more solutions

Comments

[Mathias]

@Georg: The downvote is mine, but I assure you it was not intentional! I clicked the down arrow by accident, and now the vote is "too old to change". If you would be so kind as to make a small edit, I will happily switch it to an upvote (which is what I intended to do in the first place).

[Mathias]

Thanks. That's been weighing on my conscience! :)