Beginner's Objective-C Syntax Question

Question

I came across the following code snippets from Apple's Documentation.

The Interface is fairly straightforward:

#import <Foundation/Foundation.h>
#import "ApplicationCell.h"

@interface CompositeSubviewBasedApplicationCell : ApplicationCell {
        UIView *cellContentView;
}
@end

The implementation:

#import "CompositeSubviewBasedApplicationCell.h"

@interface CompositeSubviewBasedApplicationCellContentView : UIView {
    ApplicationCell *_cell;
    BOOL _highlighted;
}

@end

@implementation CompositeSubviewBasedApplicationCellContentView
//not important, abbreviated...
@end

I can't quite figure out why there is another @interface declaration in the implementation file. I assume that it is a way of declaring private instance variable. Am I right?

And since the interface already said that CompositeSubviewBasedApplicationCell extends ApplicationCell, what does CompositeSubviewBasedApplicationCellContentView : UIView mean?

Thanks in advance.

omz · Accepted Answer · 2011-07-10 15:23:31Z

5

It's the definition of another class. In most cases, this would be in a separate file, but it's also possible to define multiple classes in one file, especially if they're closely related.

CompositeSubviewBasedApplicationCellContentView is probably not used by any classes except for CompositeSubviewBasedApplicationCell, so it doesn't need to have its own header file.

answered Jul 10, 2011 at 15:23

omz

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1 Comment

Azu Over a year ago

Oh my. I must be tired. I did not find that it's a different definition. Totally missed the "ContentView" in the end of the name. Thanks for pointing out.

Espresso · Accepted Answer · 2011-07-10 15:29:33Z

2

CompositeSubviewBasedApplicationCell and CompositeSubviewBasedApplicationCellContentView are two different classes.

I can't quite figure out why there is another @interface declaration in the implementation file. I assume that it is a way of declaring private instance variable. Am I right?

Yes, that's a way to make a class completely private. If someone wanted it to be partially private they could just extend it in the implementation file like this:

@interface CompositeSubviewBasedApplicationCell()

@end

answered Jul 10, 2011 at 15:29

Espresso

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