@interface NSObject (SJObserverHelper)

- (void)sj_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath;

@end

@interface SJObserverHelper : NSObject
@property (nonatomic, unsafe_unretained) id target;
@property (nonatomic, unsafe_unretained) id observer;
@property (nonatomic, strong) NSString *keyPath;
@property (nonatomic, weak) SJObserverHelper *factor;
@end

@implementation SJObserverHelper
- (void)dealloc {
 if ( _factor ) {
 [_target removeObserver:_observer forKeyPath:_keyPath];
 }
}
@end

@implementation NSObject (ObserverHelper)

- (void)sj_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath {
 
 [self addObserver:observer forKeyPath:keyPath options:NSKeyValueObservingOptionNew context:nil];
 
 SJObserverHelper *helper = [SJObserverHelper new];
 SJObserverHelper *sub = [SJObserverHelper new];
 
 sub.target = helper.target = self;
 sub.observer = helper.observer = observer;
 sub.keyPath = helper.keyPath = keyPath;
 helper.factor = sub;
 sub.factor = helper;
 
 const char *helpeKey = [NSString stringWithFormat:@"%zd", [observer hash]].UTF8String;
 objc_setAssociatedObject(self, helpeKey, helper, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
 objc_setAssociatedObject(observer, helpeKey, sub, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end

#import <objc/message.h>
@interface NSObject (Associate)
@property (nonatomic, strong) id tmpObj;
@end
@implementation NSObject (Associate)
static const char *testKey = "TestKey";
- (void)setTmpObj:(id)tmpObj {
 // objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)
 objc_setAssociatedObject(self, testKey, tmpObj, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (id)tmpObj {
 // objc_getAssociatedObject(id object, const void *key)
 return objc_getAssociatedObject(self, testKey);
}
@end

@interface SJObserverHelper : NSObject
@property (nonatomic, weak) id target;
@property (nonatomic, weak) id observer;
@property (nonatomic, strong) NSString *keyPath;
@end
@implementation SJObserverHelper
- (void)dealloc {
 [_target removeObserver:_observer forKeyPath:_keyPath];
}
@end
- (void)addObserver {
 NSString *keyPath = @"name";
 [_xiaoM addObserver:_observer forKeyPath:keyPath options:NSKeyValueObservingOptionNew context:nil]; 
 SJObserverHelper *helper_obj = [SJObserverHelper new];
 helper_obj.target = _xiaoM;
 helper_obj.observer = _observer;
 helper_obj.keyPath = keyPath;
 const char *helpeKey = [NSString stringWithFormat:@"%zd", [_observer hash]].UTF8String;
 // 关联
 objc_setAssociatedObject(_xiaoM, helpeKey, helper_obj, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

reason: 'An instance 0x12cd1c370 of class Person was deallocated while key value observers were still registered with it.

@interface SJObserverHelper : NSObject
@property (nonatomic, unsafe_unretained) id target;
@property (nonatomic, unsafe_unretained) id observer;
@property (nonatomic, strong) NSString *keyPath;
@end

- (void)addObserver {
 .....  
 SJObserverHelper *helper_obj = [SJObserverHelper new];
 SJObserverHelper *sub_obj = [SJObserverHelper new];
 sub_obj.target = helper_obj.target = _xiaoM;
 sub_obj.observer = helper_obj.observer = _observer;
 sub_obj.keyPath = helper_obj.keyPath = keyPath;
 const char *helpeKey = [NSString stringWithFormat:@"%zd", [_observer hash]].UTF8String;
 // 关联
 objc_setAssociatedObject(_xiaoM, helpeKey, helper_obj, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
 // 关联
 objc_setAssociatedObject(_observer, helpeKey, sub_obj, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@interface SJObserverHelper : NSObject
@property (nonatomic, unsafe_unretained) id target;
@property (nonatomic, unsafe_unretained) id observer;
@property (nonatomic, strong) NSString *keyPath;
@property (nonatomic, weak) SJObserverHelper *factor; // 1. 新增一个 weak 变量
@end

@implementation SJObserverHelper
- (void)dealloc {
 if ( _factor ) {
  [_target removeObserver:_observer forKeyPath:_keyPath];
 }
}
@end

- (void)addObserver {
 ..... 
 SJObserverHelper *helper_obj = [SJObserverHelper new];
 SJObserverHelper *sub_obj = [SJObserverHelper new];
 sub_obj.target = helper_obj.target = _xiaoM;
 sub_obj.observer = helper_obj.observer = _observer;
 sub_obj.keyPath = helper_obj.keyPath = keyPath;
 // 2. 互相 weak 引用
 helper_obj.factor = sub_obj; 
 sub_obj.factor = helper_obj;
 const char *helpeKey = [NSString stringWithFormat:@"%zd", [_observer hash]].UTF8String;
 // 关联
 objc_setAssociatedObject(_xiaoM, helpeKey, helper_obj, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
 // 关联
 objc_setAssociatedObject(_observer, helpeKey, sub_obj, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}