如何在Obj-C类别中“伪造”ivars(iPhone)

objc_setAssociatedobject()和朋友被添加到iPhone OS 3.1中,所以如果您可以选择仅定位3.1设备,那么您实际上可以执行与SNow Leopard完全相同的操作……

如果你不能,你可以创建一个静态的关联字典和猴子补丁NSObjects dealloc方法.由于各种技术原因,这种解决方案无法在GC存在的情况下正常工作(这就是苹果添加关联内容的原因),但由于iPhone不支持GC,因此不存在问题.

如果你刚刚开始研究这个项目,我强烈建议你使用运行时函数并定位3.1 plus,但如果这不是一个选项,那么这里就是你如何做的一个例子.

LGAssociativeStorage.h：

#import <pthread.h>
#import <Foundation/Foundation.h>

@interface NSObject (LGAssociativeStorage)
@property (retain) id associatedobject;
@end

LGAssociativeStorage.mm

#import <objc/runtime.h>
#import "LGAssociativeStorage.h"

/* We are using STL containers because:
   1) Using Objective C containers can cause deallocs which cause recursion issues
   2) STL containers are high perf containers that don't introduce external code dependencies
   Ideally one Could include a thread safe map implementation,but I don't need one currently
*/

#include <map>

typedef std::map<id,id> idMap_t;
typedef std::pair<id,id> idPair_t;

static NSMutableDictionary * data = nil;
static pthread_mutex_t data_lock = PTHREAD_MUTEX_INITIALIZER;
static IMP gOriginalNSObjectDealloc = nil;
static idMap_t  associatedobjectMap;

static
void removeAssociatedobjectFromMap(id self) {
  idMap_t::iterator iter = associatedobjectMap.find(self);
    if( iter != associatedobjectMap.end() ) {
        [iter->second release];
        associatedobjectMap.erase(iter);
    }
}

static
id newNSObjectDealloc(id self,SEL deallocSelector,...) {
    pthread_mutex_lock(&data_lock);
    removeAssociatedobjectFromMap(self);
    pthread_mutex_unlock(&data_lock);
    return gOriginalNSObjectDealloc(self,deallocSelector);
}

static void initIfNecessary(void) {
    if (!data) {
        data = [[NSMutableDictionary alloc] init];

        // The below line of code is abusive... in the future the Objective C runtime will use it as evidence
        // that I am an unfit software engineer and take custody of all my code
        gOriginalNSObjectDealloc = class_replaceMethod([NSObject class],@selector(dealloc),newNSObjectDealloc,"v@:");
    }
}



@implementation NSObject (LGAssociativeStorage)

- (id) associatedobject {
    id retval = nil;
    pthread_mutex_lock(&data_lock);
    initIfNecessary();
    idMap_t::iterator iter = associatedobjectMap.find(self);
    if( iter != associatedobjectMap.end() ) {
        retval = iter->second;
    }
    pthread_mutex_unlock(&data_lock);
    return retval;
}

- (void) setAssociatedobject:(id)object_ {
    pthread_mutex_lock(&data_lock);
    initIfNecessary();
    removeAssociatedobjectFromMap(self);
    [object_ retain];
    associatedobjectMap.insert(idPair_t(self,object_));
    pthread_mutex_unlock(&data_lock);   
}

@end