iOS类别属性无法识别的选择器已发送到实例

Question

我有带有属性的iOS 7.1 Objective-C类别...这里的标头代码

#import <UIKit/UIKit.h>

@interface UIViewController (CategoryName)
@property(nonatomic, copy) UITapGestureRecognizer *recognizer;

然后我有带代码的.m文件

#import "UIViewController+CategoryName.h"

@implementation UIViewController (CategoryName)
@dynamic recognizer;

...

- (void)myMethod {
    // here it crashes!!!
    self.recognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(anothermethod)];
    ...
}


...

@end

将类别导入到viewcontroller中，然后调用[self myMethod]总是会因消息而崩溃- unrecognized selector sent to instance指向myMethod中初始化self.recognizer行。

我究竟做错了什么？

Answer 1

只有一种方法可以将属性添加到Objective-C类别中 ：即使用关联的对象 。

请使用此指南来修复您的代码：

http://www.davidhamrick.com/2012/02/12/Adding-Properties-to-an-Objective-C-Category.html

另外，NSHipster在此主题上做了一个博客文章，并很好地解释了这一问题：

http://nshipster.com/associated-objects/

为了完全帮助您摆脱困境，以下是您应编写的用于解决问题的代码：

#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