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,...)

Answer 1

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