Dynamic Accessors for Category Properties

This is the source code to complement the blog post I wrote.

Using the methods defined in this NSObject category, you can simplify implementation of properties in your own categories.

Simply add the NSObject+DZLCategoryProperties to your project and in any category that you have declared properties.

If you have a category interface as in the following example:

@interface Person (XYZAdditions)
@property (strong, nonatomic) NSString *xyz_nickname;
@property (strong, nonatomic) Company *xyz_employer;
@end

The simply declare the properties as dynamic and call from +load one of the methods in this NSObject+DZLCategoryProperties category to implement the getters and setters for your properties at runtime.

@implementation Person (XYZAdditions)
@dynamic nickname;
@dynamic employer;

+ (void)load
{
  // implement for all properties (where methods are not already defined)
  [self DZL_implementDynamicPropertyAccessors];

  // or implement only for specific property specified by name
  [self DZL_implementDynamicPropertyAccessorsForPropertyName:@"xyz_nickname"];

  // or implement only for specific properties matching regular expression
  [self DZL_implementDynamicPropertyAccessorsForPropertyMatching:@"^xyz_"];
}

@end

Shorthand

Define DZL_CP_SHORTHAND in your project's precompiled header in order to take advantage of the shorthand versions of the method described above, for example:

In MyAwesomeApp-Prefix.pch

#define DZL_CP_SHORTHAND

This allows you to use the following shorthand methods:

• +[NSObject implementDynamicPropertyAccessors]
• +[NSObject implementDynamicPropertyAccessorsForPropertyName:]
• +[NSObject implementDynamicPropertyAccessorsForPropertyMatching:]

The problem that this solves

Usually, you might define a simple object-type property in a category as follows:

@interface UIView (DZLAdditions)
@property (strong, nonatomic) NSString *name;
@end

static const void *nameKey = &nameKey;

@implementation UIView (DZLAdditions)

- (NSString *)name
{
  return objc_getAssociatedObject(self, nameKey);
}

- (void)setName:(NSString *)name
{
  objc_setAssociatedObject(self, nameKey, name, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end

If you add multiple properties, you have to define the getter and setter for each property. And the worst bit is that all these getters and setters will look almost identical.

Installing

Add the NSObject+DZLCategoryProperties directory to your project, and optionally define DZL_CP_SHORTHAND in your project's precompiled header file.

Finally...

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