category with no name in the class's .m file

Question

what does it mean to create a category like this: @interface myClass () ... @end in the same class's .m file ? this category may contain methods and properties, why not to add these methods and properties directly in the class's .h file ?

thank you in advance.

score 2 · Accepted Answer · answered Feb 20 '12 at 08:18

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It's basically a workaround for Objective-C's lack of private methods. You put classes in there to hide them from users of the class. They can technically still use them (although they'll get a warning) but if they don't know about them, they probably won't.

answered Feb 20 '12 at 08:18

Randall

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why not add a name for it though ? – JAHelia Feb 20 '12 at 08:19
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Check out this answer http://stackoverflow.com/questions/1052233/iphone-obj-c-anonymous-category-or-private-category – Randall Feb 20 '12 at 08:20

score 2 · Answer 2 · answered Feb 20 '12 at 08:35

Sometimes i would do this when i had a private method.

Because,if the method not define in header,when you call it in implementation,you got a warning, (your method's code is above your invoked).

like this:Instance method '-XXX' not found (return type defaults to 'id')

So,for no warning,i put a method define in a category maybe i will write a @interface myClass(private).

score 1 · Answer 3 · answered Feb 20 '12 at 08:18

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If there is no name in the parenthesis it is a class extension. If you define a name then it is a category.

The most common reason to do this is to hide instance variables and methods. To make the appear to be private.

answered Feb 20 '12 at 08:18

Markus Persson

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category with no name in the class's .m file

3 Answers3