函数式编程的KVO+自动销毁机制

系统KVO这个响应式的机制很有挖掘的潜力,最近在这上面花了一点时间,总结一下自己的一些心得

* 系统KVO

- (void)viewDidLoad {
    [super viewDidLoad];
    self.p = [[Peroson alloc] init];
    [self addObserver:self forKeyPath:@"name" options:(NSKeyValueObservingOptionNew) context:nil];
    self.p.name = @"Cooci";
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{
    // value
    NSLog(@"%@",change);
}

还有KVO开关

//KVO的自动开关
+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key{
    if ([key isEqualToString:@"age"]) {
        //返回NO就不会自动观察 这样就可以灵活敏捷开发
        return NO;
    }
    return YES;
}
- (void)setAge:(int)age{
    //自动开关关闭, 还可以通过手动开关监听
    [self willChangeValueForKey:@"age"];
    _age = age;
    [self didChangeValueForKey:@"age"];
}

//对于对象嵌套对象,只需要观察对象的对象 就可以观察到嵌套层的对象的属性
+ (NSSet<NSString *> *)keyPathsForValuesAffectingValueForKey:(NSString *)key{
    NSSet *sets = [super keyPathsForValuesAffectingValueForKey:key];
    if ([key isEqualToString:@"dog"]){
        //嵌套层的处理
        NSSet *affectingKeys = [NSSet setWithObjects:@"_age", @"_name",nil];
        sets = [sets setByAddingObjectsFromSet:affectingKeys];
    }
    return sets;
}

数组的观察 需要借助KVC,mutableArrayValueForKey KVC的数组取值方式，要实现KVO必须通过KVC对数据进行操作.

[self.p addObserver:self forKeyPath:@"arrs" options:(NSKeyValueObservingOptionNew) context:nil];
[[self.p mutableArrayValueForKey:@"arrs"] addObject:@"Cooci"];
[[self.p mutableArrayValueForKey:@"arrs"] removeObject:@"Cooci"];

数组观察的kind 数组的移除

typedef NS_ENUM(NSUInteger, NSKeyValueSetMutationKind) {
    NSKeyValueUnionSetMutation = 1, //setter
    NSKeyValueMinusSetMutation = 2, //add
    NSKeyValueIntersectSetMutation = 3,//remove
    NSKeyValueSetSetMutation = 4 //set集合类
};

KVO的原理:

• 1:动态生成子类----NSKVONotifying_A //可以通过isa查看
• 2:setter方法的添加
• 3:消息转发给父类

• 自定义KVO --- 猜测实现

//利用函数式编程思想,这里添加观察的代码与逻辑代码可以放到一起
- (void)kc_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath withBlock:(KCKVOBlock)block;

[self.p kc_addObserver:self forKeyPath:@"name" withBlock:^(id observer, NSString *keyPath, id newValue, id oldValue) {
    //逻辑代码区域
}];

//核心代码的实现

- (void)kc_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath withBlock:(KCKVOBlock)block{

    //实例
    //setter keypath是否 刷掉实例  name
    //SEL 方法选择器  ====>  找方法  方法编号
    
    SEL setterSeletor = NSSelectorFromString(setterfromGetter(keyPath));
    Method setterMethod = class_getInstanceMethod(object_getClass(self), setterSeletor);
    if (!setterMethod) {
        @throw [NSException exceptionWithName:NSInvalidArgumentException reason:@"没有setter方法,可能是实例变量" userInfo:nil];
    }
    
    //2:动态创建子类
    
    NSString *superClassName = NSStringFromClass([self class]);
    
    Class newClas = [self creatClassFromSuperClass:superClassName];
    
    if (newClas) {
        //ias swilzing 替换父类
        object_setClass(self, newClas);
    }
    
    const char *types = method_getTypeEncoding(setterMethod);
    
    //3:setter方法
    if (![self hasSeletor:setterSeletor]) {
        class_addMethod(newClas, setterSeletor, (IMP)KCKVO_Setter, types);
    }
    //4;消息转发
    
    KCInfo *info = [[KCInfo alloc] initWithObserver:observer keyPath:keyPath observerHandle:block];
    info.target = self;

    NSMutableArray *obserArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kKVOAssioKey));

    if (!obserArray) {

        obserArray = [NSMutableArray arrayWithCapacity:1];

        /**
         关联属性
         1:对象
         2:关键字
         3:关联对象
         4:策略
         */
        objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kKVOAssioKey), obserArray, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }

    [obserArray addObject:info];
}

//其他代码也给大家粘出来:主要封装了动态生成类的方法,以及过滤方法,还有setter方法得到getter属性,getter属性===>>setter:方法的函数实现.还有动态子类添加的setter的IMP的函数,一个class的IMP函数

- (Class)creatClassFromSuperClass:(NSString *)superName{
    
    Class superClass = NSClassFromString(superName);

    /**
     动态生成类
     1:父类
     2:名字
     3:空间
     
     */
    // NSKVONotifiying_   ===>>> KCKVC_
    NSString *newClassName = [kcKVOPrefix stringByAppendingString:superName];
    Class newClass = NSClassFromString(newClassName);
    if (newClass) {
        return newClass;
    }
    
    newClass = objc_allocateClassPair(superClass, newClassName.UTF8String, 0);
    
    //添加Class
    Method classMethod = class_getClassMethod(superClass, @selector(class));
    
    const char *type = method_getTypeEncoding(classMethod);
    /**
     添加方法
     1:类
     2:方法名字
     3:IMP  函数实现的指针
     4:类型
     */
    class_addMethod(newClass, @selector(class), (IMP)KCKVC_Class, type);
    
    //注册类
    objc_registerClassPair(newClass);
    
    return newClass;
}

- (BOOL)hasSeletor:(SEL)setterSeletor{
    
    Class observerClass = object_getClass(self);
    
    unsigned int methodCount = 0;
    
    Method *methodList = class_copyMethodList(observerClass, &methodCount);
    
    for (int i = 0; i<methodCount; i++) {
        SEL sel = method_getName(methodList[i]);
        if (setterSeletor == sel) {
            free(methodList);
            return YES;
        }
    }
    free(methodList);
    return NO;
}


#pragma mark 函数去区域

static Class KCKVC_Class(id self){
    return class_getSuperclass(object_getClass(self));
}

- (void)setName:(NSString *)str{
    
}

static void KCKVO_Setter(id self,SEL _cmd,id newValue){
    
    //手动监听
    //_cmd ===
    
    
    NSString *setterName = NSStringFromSelector(_cmd);
    NSString *getterName = getterfromSetter(setterName);
    
    id oldValue = [self valueForKey:getterName];

    [self willChangeValueForKey:getterName];
    //消息转发
    
    void(*KCMsgSend)(void *,SEL,id) = (void *)objc_msgSendSuper;
    
    struct objc_super kcSuperStruct = {
        .receiver = self,
        .super_class = class_getSuperclass(object_getClass(self))
    };

    KCMsgSend(&kcSuperStruct,_cmd,newValue);
    [self didChangeValueForKey:getterName];
    
    NSMutableArray *obserArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kKVOAssioKey));
    
//    NSMutableArray *obserArray = [KCInfoShare shared].infoArray;
    for (KCInfo *info in obserArray) {
        dispatch_async(dispatch_queue_create(0, 0), ^{
            info.blockHandle(self, info.keyPath, newValue, oldValue);
        });
    }

}


//name ===>> setName:
static NSString * setterfromGetter(NSString * getter){
    
    if (getter.length <= 0) { return nil;}
    
    //name
    NSString *firtString = [[getter substringToIndex:1] uppercaseString];
    NSString *leaveString = [getter substringFromIndex:1]; //ame
    
    return [NSString stringWithFormat:@"set%@%@:",firtString,leaveString];
    
}


//setName: ===>>> name
static NSString * getterfromSetter(NSString * setter){
    
    if (setter.length <= 0 || ![setter hasPrefix:@"set"] || ![setter hasSuffix:@":"]) { return nil;}
    
    //setName:  ===>> Name:  ====> Name ==> name
    
    NSRange range = NSMakeRange(3, setter.length-4);
    NSString *getter = [setter substringWithRange:range];
    NSString *firstString = [[getter substringToIndex:1] lowercaseString]; //n
    getter = [getter stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:firstString];

    return getter;
    
}

//这里的增加了一个信息保存的类KCInfo

@interface KCInfo:NSObject
@property (nonatomic, copy) NSString *keyPath;
@property (nonatomic, copy) KCKVOBlock blockHandle;
@property (nonatomic, weak) NSObject *observer;
@property (nonatomic, unsafe_unretained) NSObject *target;
@property (nonatomic, weak) KCInfo   *info;
@property (nonatomic, strong) NSMutableArray *obserArray;
@end

@implementation KCInfo

- (instancetype)initWithObserver:(NSObject *)observer keyPath:(NSString *)keyPath observerHandle:(KCKVOBlock)blockHandle{
    if (self = [super init]) {
        _keyPath = keyPath;
        _observer = observer;
        _blockHandle = blockHandle;
    }
    return self;
}
@end

//为了保障整个代码的完善性:添加移除的方法

- (void)kc_removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath{
    //KCInfo保存的数据是不是要移除
    NSMutableArray *obserArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kKVOAssioKey));
    //删除一个还是可以的,但是删除多个是会出现是异常的。（会出现索引跳位）
    [obserArray enumerateObjectsUsingBlock:^(KCInfo *info, NSUInteger idx, BOOL * _Nonnull stop) {
        if ([info.keyPath isEqualToString:keyPath]&&[info.observer isEqual:observer]) {
            [obserArray removeObject:info];
        }
    }];
    if (obserArray.count == 0)  obserArray = nil;
    //要将动态子类的isa指针 指回来Person
    NSString *nowClassName = NSStringFromClass(object_getClass(self));
    NSString *superClassName = [nowClassName stringByReplacingOccurrencesOfString:kcKVOPrefix withString:@""];
    Class superClass = NSClassFromString(superClassName);
    object_setClass(self, superClass);
    NSLog(@"%@",observer);
}

//其实添加这个销毁方法还不是我希望的,我希望每一次用就起,不用这个KVO自动销毁

 //利用runtime的机制我拦截Person的dealloc方法
  Method m2 = class_getInstanceMethod(newClas, @selector(myDealloc));
Method m1 = class_getInstanceMethod(newClas, NSSelectorFromString(@"dealloc"));
method_exchangeImplementations(m2, m1);

- (void)myDealloc{
    //要将动态子类的isa指针 指回来Person
    NSString *nowClassName = NSStringFromClass(object_getClass(self));
    NSString *superClassName = [nowClassName stringByReplacingOccurrencesOfString:kcKVOPrefix withString:@""];
    Class superClass = NSClassFromString(superClassName);
    object_setClass(self, superClass);
    
    //KCInfo保存的数据是不是要移除
    NSMutableArray *obserArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kKVOAssioKey));
    //删除一个还是可以的,但是删除多个是会出现是异常的。（会出现索引跳位）
    [obserArray removeAllObjects];
    
    [self myDealloc];
}

方法交换

//最后通过类搜索与isa的判别发现与系统的KVO相差无几

unsigned int outCount;
//该函数的作用是获取所有已注册的类
Class *classes = objc_copyClassList(&outCount);
for (int i = 0; i < outCount; i++) {
    NSLog(@"%s", class_getName(classes[i]));
}
free(classes);

写到这里也就完成了,以上就是我对KVO的理解,希望大家能给与指正