CODEWITHSUNDEEP
objective-ccocoaimportheader-files
samir
samir

Reputation: 4551

What is an import statement where filename contains "+"?

I have seen in some source code (by other developers) something like this: 

#import "SomeClass+SomeOtherClass.h"

What is the + for? What does this mean?

Upvotes: 3

Views: 137

Answers (2)

Dr.Kameleon
Dr.Kameleon

Reputation: 22820

The "+" in header/source filenames is - by convention - used to describe Category implementations.

Example :

Let's say you want to add some functionality to an existing class (e.g.the NSString class). (NSString+Utilities.h)

// NSString+Utilities.h

@interface NSString (Utilities)
-(NSString *) doSthWithThisString;
@end

// NSString+Utilities.m

@implementation NSString (Utilities)

-(NSString *) doSthWithThisString
{
  NSMutableString *transformedStr = [self copy];

  // Do sth

  return transformedStr;
}

@end

Using it :

// in another file

#import "NSString+Utilities.h"

- (void)awakeFromNib
{
    NSString* myString = @"This is a string";

    // you may use our new NSString method as much as any already-existing one
    NSString* newString = [myString doSthWithThisString];
}

Reference :

Upvotes: 4

sch
sch

Reputation: 27536

Let's say you want to add functionality to an existing class (exp: NSString). You can do that by creating a subclass or you can use a category. And it is common to name the file where the category is defined using the pattern : MyClass+MyCategory.h.

For example, we can add a method reverseString to the class NSString in a category:

// File NSString+reversable.h
- (NSString *)reverseString;

// File NSString+reversable.m
- (NSString *)reverseString
{
    // Implementation
}

Have a look at this documentation for more information about categories.

Then you can use that category in another class:

#import "NSString+reversable.h"
// ...

NSString *aString = @"Hello!";
NSString *reversedString = [aString reverseString];

Upvotes: 4

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