Extend UIView and add property in iOS

Question

I would like to add one property to UIView. I know I could subclass an UIView but as I want to add onelly one property I would like just to extend it.

I try like this :

@interface UIView (Util)
@property(nonatomic, assign) BOOL isShow;
@end

@implementation UIView (Util)
@dynamic isShow;

-(void)setIsShow:(BOOL)isShow{
    self.isShow = isShow;
}
@end

but it doesn't work. It throw an exception : Thread 1: EXC_BAD_ACCESS(code=2,address,...)

possible duplicate of [Objective-C: Property in Category](http://stackoverflow.com/questions/8733104/objective-c-property-in-category) — Amar, Dec 04 '13 at 10:49

Ivan Genchev · Accepted Answer · 2013-12-04T10:47:41.940

If you want to add a new property in a category you'll have to use objc_setAssociatedObject and objc_getAssociatedObject.

Example:

NSString *const IS_SHOW_KEY = @"IS_SHOW";

@interface UIView (Util)
@property (nonatomic) BOOL isShow;
@end

@implementation UIView (Util)

- (void)setIsShow:(BOOL)isShow {
    NSNumber *val = @(isShow);
    objc_setAssociatedObject(self, (__bridge const void*)(IS_SHOW_KEY), val, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (BOOL)isShow {
    NSNumber *val = objc_getAssociatedObject(self, (__bridge const void*)IS_SHOW_KEY);
    return [val boolValue];
}

@end

See the docs for the Runtime Reference here: https://developer.apple.com/library/ios/documentation/cocoa/reference/ObjCRuntimeRef/Reference/reference.html

Thank you. This is it. For all others you should include `#import ` — Marko Zadravec, Dec 04 '13 at 11:01

score 0 · Answer 2 · answered Dec 04 '13 at 10:41

You should not add properties through category - you can only add methods. Read more here:

http://developer.apple.com/library/ios/#documentation/General/Conceptual/DevPedia-CocoaCore/Category.html

You can however achieve what you need by creating methods for setting / getting values you need.

@interface UIView (Util)
-(void)setIsShow:(BOOL)isShow;
@end

@implementation UIView (Util)
@dynamic isShow;

-(void)setIsShow:(BOOL)isShow{
    self.isShow = isShow;
}
@end

If you really need properties, than you need to subclass

Extend UIView and add property in iOS

2 Answers2