iOS category property unrecognized selector sent to instance - ios

Question

I've Objective-C category for iOS 7.1 with property...here's header code
#import <UIKit/UIKit.h>
#interface UIViewController (CategoryName)
#property(nonatomic, copy) UITapGestureRecognizer *recognizer;
then I've .m file with code
#import "UIViewController+CategoryName.h"
#implementation UIViewController (CategoryName)
#dynamic recognizer;
...
- (void)myMethod {
// here it crashes!!!
self.recognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(anothermethod)];
...
}
...
#end
Importing category into viewcontroller and then calling [self myMethod] always crashes with message - unrecognized selector sent to instance pointing to line in myMethod where self.recognizer is initialized.
What am I doing wrong?

Answer 1

There's only 1 way to add properties to an objective-c category: that is by using associated objects.
Please use this guide to fix your code:
http://www.davidhamrick.com/2012/02/12/Adding-Properties-to-an-Objective-C-Category.html
Also, NSHipster did a blogpost on this subject and explains this matter really well:
http://nshipster.com/associated-objects/
To completely help you out of trouble, here's the code you should write to fix your problem:
#import <objc/runtime.h>
NSString * const recognizerPropertyKey = #"recognizerPropertyKey";
#implementation UIViewController (CategoryName)
#dynamic recognizer;
- (void)setRecognizer:(UITapGestureRecognizer *)recognizer {
objc_setAssociatedObject(self, (__bridge const void *)(recognizerPropertyKey), recognizer, OBJC_ASSOCIATION_COPY);
}
- (UITapGestureRecognizer *)recognizer {
return objc_getAssociatedObject(self, (__bridge const void *)(recognizerPropertyKey));
}
#end