Objective-c – Fast enumeration in OS 3.0

iphoneiphone-sdk-3.0objective c

I just tried compileing my iPhone app against OS 3.0 and I get a compile error when using fast enumeration.

I'm trying to go through an NSArray containing cComment classes:

for (cComment* newComment in comments.comments)

And I get this error

error: type of accessor does not match the type of property 'comments'.

This works flawlessly when compiled with OS 2.2.1.

I understand the error, the enumaretion isn't strongly typed but since as far as I know generics/templates are not supported in objective-c. So currently I can only see one way around this:

for (id commentObject in comments.comments)
{
     cComment *newComment = (cComment *)commentObject;
}

Can anyone think of another way? Why has this changed? Any points to apple documentation about this change would be appreciated.

EDIT

Following Grouchal suggestion i tried this:
NSArray* allComments = comments.comments
and I got the same error so it seems its not about the enumeration after all

here's the code form the header file:

NSMutableArray *comments;

@property (readonly,nonatomic) NSArray* comments;

and the property is synthesized in the implementation file.

Changing the property to NSMutableArray seems to solve the problem but I don't see any reason why this should be the case. Any ideas.

Thanks.

Best Answer

The problem is in the property definition. You should change have it as:

@property (readonly,nonatomic) NSMutableArray* comments

On the downside, your array will be exposed as mutable (though I suppose that's what you wanted to prevent).

Related Solutions

Objective-C changes between OS 2.2.1 and OS 3

This is a compiler bug.

Though you didn't specify it completely, I expect your code looks like this:

@interface Foo : NSObject {
    NSMutableArray *objects;
}
@property (readonly, copy) NSArray *objects;
@end

@implementation Foo
@synthesize objects;
@end

The compiler is, unfortunately, confused between the declaration of the objects property and the declaration of the objects instance variable. Remember that properties and instance variables are different things in Objective-C; a property can be backed by an instance variable, but it's really part of the public interface of a class.

You can work around this by changing your code to clearly separate the definition of the instance variable from the definition of the property, for example by prefixing the name of the instance variable:

@interface Foo : NSObject {
    NSMutableArray *_objects;
}
@property (readonly, copy) NSArray *objects;
@end

@implementation Foo
@synthesize objects = _objects;
@end

This way the compiler doesn't get confused about the property versus the instance variable in expressions like self.objects (which it shouldn't anyway, but apparently does).

Just to head off the inevitable response: Apple does not reserve the underbar prefix for instance variables. It's reserved for methods. Regardless, if you dislike the underbar, feel free to use another prefix.

Objective-c – Weird error for UIActionSheets when compiling against iPhone 3.0 OS

You've got a blatant error on this line:

UIApplication* app = [[UIApplication sharedApplication] delegate];

You're getting an instance of UIApplication, requesting its delegate, and then trying to assign the delegate into a UIApplication pointer.

It should be:

id<UIApplicationDelegate> app = [[UIApplication sharedApplication] delegate];

I'm not sure it'll exactly fix your error, but it's sure not correct the way you have it. =)

Related Topic

Ios – Works in OS 2.2.1 but not in OS 3.0: Error: type of accessor