@class vs. #import

by

If you see this warning:

warning: receiver ‘MyCoolClass’ is a forward class and corresponding @interface may not exist

you need to #import the file, but you can do that in your implementation file (.m), and use the @class declaration in your header file.

@class does not (usually) remove the need to #import files, it just moves the requirement down closer to where the information is useful.

For Example

If you say @class MyCoolClass, the compiler knows that it may see something like:

MyCoolClass *myObject;

It doesn’t have to worry about anything other than MyCoolClass is a valid class, and it should reserve room for a pointer to it (really, just a pointer). Thus, in your header, @class suffices 90% of the time.

However, if you ever need to create or access myObject‘s members, you’ll need to let the compiler know what those methods are. At this point (presumably in your implementation file), you’ll need to #import "MyCoolClass.h", to tell the compiler additional information beyond just “this is a class”.

More Related Contents:

  1. How does an underscore in front of a variable in a cocoa objective-c class work?
  2. NSString property: copy or retain?
  3. Having trouble adding objects to NSMutableArray in Objective C
  4. How to print out the method name and line number and conditionally disable NSLog?
  5. How to Check if an NSDate occurs between two other NSDates
  6. Deep copying an NSArray
  7. setValue:forUndefinedKey: this class is not key value coding-compliant for the key [duplicate]
  8. @synthesize vs @dynamic, what are the differences?
  9. How to find out who called a method?
  10. Managing multiple asynchronous NSURLConnection connections
  11. self.variable and variable difference [duplicate]
  12. Is there a way to suppress warnings in Xcode?
  13. Sorting two NSArrays together side by side
  14. Difference between self.var and simply var
  15. If “a == b” is false when comparing two NSString objects
  16. Avoiding “NSArray was mutated while being enumerated”
  17. With ARC, what’s better: alloc or autorelease initializers?
  18. 2D arrays using NSMutableArray
  19. Removing duplicates from NSMutableArray
  20. Call instance method from class method
  21. NSPrivateQueueConcurrencyType Not saving properly
  22. Properties and Instance Variables in Objective-C
  23. Looping using NSRange
  24. What’s the difference between [NSNull null] and nil?
  25. Class method equivalent of -respondsToSelector:
  26. +[NSString stringWithString:] — what’s the point?
  27. How to do a natural sort on an NSArray?
  28. What’s the difference between #import and @class, and when should I use one over the other?
  29. How to Get the Display Name with the Display ID in Mac OS X?
  30. Executing shell commands with NSTask – Objective-C Cocoa

Leave a Comment