Objective-c Category (categories)

Category is one of the most commonly used functions in objective-c.

The category can add methods to existing classes without adding a subclass.

The standard syntax format for the category interface is as follows:

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1. #import "class name. h"
2. @interface class name (category name)
3. Declaration of the new method
4. @end

The categories are implemented as follows:

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1. #import "class name Category name. h"
2. @implementation class name (category name)
3. New Method implementation
4. @end

This is very similar to the definition of a class, except that the category has no parent class , and that there is a category name in parentheses. Names can be taken casually.

For example: if we want to add a method to the NSString to determine whether it is a URL, then you can do this:

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1. #import ...
2. @interface NSString (Utilities)
3. -(BOOL) Isurl;
4. @end

Category implementations:

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1. #import "NSStringUtilities.h"
2. @implementation NSString (Utilities)
3. -(BOOL) isurl{
4. if ([Self hasprefix:@"/http"])
5. return YES;
6. Else
7. return NO;
8. }
9. @end

How to use:

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2. nsstring* string1 = @"http://www.csdn.net";
4. nsstring* string2 = @"Pixar";
8. if ([string1 Isurl])
10. NSLog (@"string1 is a URL");
12. Else
14. NSLog (@"string1 is not a URL");
18. if ([string2 Isurl])
20. NSLog (@"string2 is a URL");
22. Else
24. NSLog (@"string2 is not a URL");

Objective-c Category (categories)