objc_setAssociatedObject

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objc_setAssociatedObject 是什么

可以动态的给一个对象增加成员变量和成员方法。

Sets an associated value for a given object using a given key and association policy.

OBJC_EXPORT void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)
OSX_AVAILABLE_STARTING(MAC_10_6, __IPHONE_3_1);

Returns the value associated with a given object for a given key.
OBJC_EXPORT id objc_getAssociatedObject(id object, const void *key)
OSX_AVAILABLE_STARTING(MAC_10_6, __IPHONE_3_1);

使用方法

导入头文件

#import <objc/runtime.h>头文件

objc_setAssociatedObject需要四个参数：源对象，关键字，关联的对象和一个关联策略。

1 源对象alert
2 关键字 唯一静态变量key associatedkey
3 关联的对象 sender
4 关键策略 OBJC_ASSOCIATION_ASSIGN

例子1

给一个对象新增成员变量

BHAPI+PXExtension.h

@interface BINGO_FITNESS_COURSE (PXExtension)

@property (nonatomic, copy) NSString *title;
@property (nonatomic, copy) NSString *lockImage;

@end

BHAPI+PXExtension.m

@implementation BINGO_FITNESS_COURSE (PXExtension)

- (NSString *)title
{
    return objc_getAssociatedObject(self, _cmd);
}

- (void)setTitle:(NSString *)title
{
    objc_setAssociatedObject(self, @selector(title), title, OBJC_ASSOCIATION_COPY);
}

- (NSString *)lockImage
{
    return objc_getAssociatedObject(self, _cmd);
}

- (void)setLockImage:(NSString *)lockImage
{
    objc_setAssociatedObject(self, @selector(lockImage), lockImage, OBJC_ASSOCIATION_COPY);
}

@end

_cmd在Objective-C的方法中表示当前方法的selector(函数指针)

上面例子中 _cmd 也可以换成一个唯一的key值如 &titleKey lockImageKey

例子2

给一个对象新增方法

UIAlertView+Block.h

#import <UIKit/UIKit.h>
typedef void (^successBlock)(NSInteger buttonIndex);

@interface UIAlertView (Block)<UIAlertViewDelegate>

- (void)showWithBlock:(successBlock)block;

@end

UIAlertView+Block.m

#import "UIAlertView+Block.h"
#import <objc/runtime.h>

static const char alertKey;

@implementation UIAlertView (Block)

- (void)showWithBlock:(successBlock)block
{
    if (block)
    {
        objc_setAssociatedObject(self, &alertKey, block, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
        self.delegate = self;
    }

    [self show];
}

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    successBlock block = objc_getAssociatedObject(self, &alertKey);

    block(buttonIndex);
}

@end