13.OC底层->KVO与KVC

KVO

文档地址

• KVO 全程Key-Value-Observing，俗称"键值监听"，可以用于监听某个对象属性值得改变

• KVO的简单使用

#import "ViewController.h"
#import "MJPerson.h"

@interface ViewController ()
@property (strong, nonatomic) MJPerson *person1;
@property (strong, nonatomic) MJPerson *person2;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.person1 = [[MJPerson alloc] init];
    self.person1.age = 1;
    self.person1.height = 11;
    
    self.person2 = [[MJPerson alloc] init];
    self.person2.age = 2;
    self.person2.height = 22;
    
    // 给person1对象添加KVO监听
    NSKeyValueObservingOptions options = NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld;
    [self.person1 addObserver:self forKeyPath:@"age" options:options context:@"123"];
    [self.person1 addObserver:self forKeyPath:@"height" options:options context:@"456"];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    self.person1.age = 20;
    self.person2.age = 20;
    
    self.person1.height = 30;
    self.person2.height = 30;
}

- (void)dealloc {
    [self.person1 removeObserver:self forKeyPath:@"age"];
    [self.person1 removeObserver:self forKeyPath:@"height"];
}

// 当监听对象的属性值发生改变时，就会调用
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context
{
    NSLog(@"监听到%@的%@属性值改变了 - %@ - %@", object, keyPath, change, context);
}

@end


#import <Foundation/Foundation.h>

@interface MJPerson : NSObject
@property (assign, nonatomic) int age;
@property (assign, nonatomic) int height;
@end

• 未使用KVO监听的对象

• 使用了KVO监听的对象

• 使用了KVO监听的实例对象的isa指针指向的是NSKVONotifying_XXX类对象

• 未使用KVO监听的实例对象的isa指针指向的时XXX类对象

• NSKVONotifying_XXX类内部方法调用猜想

• 调用顺序

• 查看_NSSet *AndNotify的存在

• _NSSet *ValueAndNotify的内部实现

• KVO原理 动态⽣成⼦类:NSKVONotifiy_A 2:给动态⼦类添加Setter⽅法 3:消息转发给⽗类(runtime消息转发) 1:防⽌实例变量的影响,我添加断⾔异常排除 2;动态⼦类的过程: A:⽣成类 B:添加Class⽅法 C:注册 

KVO自定义

• 进入Foundation库发现KVO主要是这几个方法的实现，现在主要是写一个分类来模拟实现这几个方法练习。
• 创建分类文件

1.h文件方法

• 仿写三个方法

#import <Foundation/Foundation.h>

#import "LGKVOInfo.h"

NS_ASSUME_NONNULL_BEGIN

@interface NSObject (LGKVO)

- (void)lg_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(LGKeyValueObservingOptions)options context:(nullable void *)context;

- (void)lg_observeValueForKeyPath:(nullable NSString *)keyPath ofObject:(nullable id)object change:(nullable NSDictionary<NSKeyValueChangeKey, id> *)change context:(nullable void *)context;

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

@end

NS_ASSUME_NONNULL_END

• .m方法实现

#import "NSObject+LGKVO.h"
#import <objc/message.h>

static NSString *const kLGKVOPrefix = @"LGKVONotifying_";
static NSString *const kLGKVOAssiociateKey = @"kLGKVO_AssiociateKey";

@implementation NSObject (LGKVO)

- (void)lg_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(LGKeyValueObservingOptions)options context:(nullable void *)context{
    
    // 1: 验证是否存在setter方法 : 不让实例进来
    [self judgeSetterMethodFromKeyPath:keyPath];
    // 2: 动态生成子类
    Class newClass = [self createChildClassWithKeyPath:keyPath];
    // 3: isa的指向 : LGKVONotifying_LGPerson
    object_setClass(self, newClass);
    // 4: 保存观察者信息
    LGKVOInfo *info = [[LGKVOInfo alloc] initWitObserver:observer forKeyPath:keyPath options:options];
    //5.获取关联的hasMap作为存储的地方来保存这个观察者，从而打破了循环引用。
    NSMutableArray *observerArr = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey));
    
    if (!observerArr) {
        observerArr = [NSMutableArray arrayWithCapacity:1];
        [observerArr addObject:info];
        objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey), observerArr, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }

}

- (void)lg_observeValueForKeyPath:(nullable NSString *)keyPath ofObject:(nullable id)object change:(nullable NSDictionary<NSKeyValueChangeKey, id> *)change context:(nullable void *)context{
    
}


- (void)lg_removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath{
    
    NSMutableArray *observerArr = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey));
    if (observerArr.count<=0) {
        return;
    }
    
    for (LGKVOInfo *info in observerArr) {
        if ([info.keyPath isEqualToString:keyPath]) {
            [observerArr removeObject:info];
            objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey), observerArr, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
            break;
        }
    }

    if (observerArr.count<=0) {
        // 指回给父类
        Class superClass = [self class];
        object_setClass(self, superClass);
    }
}

#pragma mark - 验证是否存在setter方法
- (void)judgeSetterMethodFromKeyPath:(NSString *)keyPath{
    Class superClass    = object_getClass(self);
    SEL setterSeletor   = NSSelectorFromString(setterForGetter(keyPath));
    Method setterMethod = class_getInstanceMethod(superClass, setterSeletor);
    if (!setterMethod) {
        @throw [NSException exceptionWithName:NSInvalidArgumentException reason:[NSString stringWithFormat:@"老铁没有当前%@的setter",keyPath] userInfo:nil];
    }
}

#pragma mark -
- (Class)createChildClassWithKeyPath:(NSString *)keyPath{
    
    NSString *oldClassName = NSStringFromClass([self class]);
    NSString *newClassName = [NSString stringWithFormat:@"%@%@",kLGKVOPrefix,oldClassName];
    Class newClass = NSClassFromString(newClassName);
    // 防止重复创建生成新类
    if (newClass) return newClass;
    /**
     * 如果内存不存在,创建生成
     * 参数一: 父类
     * 参数二: 新类的名字
     * 参数三: 新类的开辟的额外空间
     */
    // 2.1 : 申请类
    newClass = objc_allocateClassPair([self class], newClassName.UTF8String, 0);
    // 2.2 : 注册类
    objc_registerClassPair(newClass);
    // 2.3.1 : 添加class : class的指向是LGPerson
    SEL classSEL = NSSelectorFromString(@"class");
    Method classMethod = class_getInstanceMethod([self class], classSEL);
    const char *classTypes = method_getTypeEncoding(classMethod);
    class_addMethod(newClass, classSEL, (IMP)lg_class, classTypes);
    // 2.3.2 : 添加setter
    SEL setterSEL = NSSelectorFromString(setterForGetter(keyPath));
    Method setterMethod = class_getInstanceMethod([self class], setterSEL);
    const char *setterTypes = method_getTypeEncoding(setterMethod);
    class_addMethod(newClass, setterSEL, (IMP)lg_setter, setterTypes);
    return newClass;
}

static void lg_setter(id self,SEL _cmd,id newValue){
    NSLog(@"来了:%@",newValue);
    // 4: 消息转发 : 转发给父类
    // 改变父类的值 --- 可以强制类型转换
    NSString *keyPath = getterForSetter(NSStringFromSelector(_cmd));
    id oldValue       = [self valueForKey:keyPath];
    
    void (*lg_msgSendSuper)(void *,SEL , id) = (void *)objc_msgSendSuper;
    // void /* struct objc_super *super, SEL op, ... */
    struct objc_super superStruct = {
        .receiver = self,
        .super_class = class_getSuperclass(object_getClass(self)),
    };
    //objc_msgSendSuper(&superStruct,_cmd,newValue)
    lg_msgSendSuper(&superStruct,_cmd,newValue);
    // 1: 拿到观察者
    NSMutableArray *observerArr = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey));
    
    for (LGKVOInfo *info in observerArr) {
        if ([info.keyPath isEqualToString:keyPath]) {
            dispatch_async(dispatch_get_global_queue(0, 0), ^{
                NSMutableDictionary<NSKeyValueChangeKey,id> *change = [NSMutableDictionary dictionaryWithCapacity:1];
                // 对新旧值进行处理
                if (info.options & LGKeyValueObservingOptionNew) {
                    [change setObject:newValue forKey:NSKeyValueChangeNewKey];
                }
                if (info.options & LGKeyValueObservingOptionOld) {
                    [change setObject:@"" forKey:NSKeyValueChangeOldKey];
                    if (oldValue) {
                        [change setObject:oldValue forKey:NSKeyValueChangeOldKey];
                    }
                }
                // 2: 消息发送给观察者
                SEL observerSEL = @selector(lg_observeValueForKeyPath:ofObject:change:context:);
                objc_msgSend(info.observer,observerSEL,keyPath,self,change,NULL);
            });
        }
    }
    
}

Class lg_class(id self,SEL _cmd){
    return class_getSuperclass(object_getClass(self));
}

#pragma mark - 从get方法获取set方法的名称 key ===>>> setKey:
static NSString *setterForGetter(NSString *getter){
    
    if (getter.length <= 0) { return nil;}
    
    NSString *firstString = [[getter substringToIndex:1] uppercaseString];
    NSString *leaveString = [getter substringFromIndex:1];
    
    return [NSString stringWithFormat:@"set%@%@:",firstString,leaveString];
}

#pragma mark - 从set方法获取getter方法的名称 set<Key>:===> key
static NSString *getterForSetter(NSString *setter){
    
    if (setter.length <= 0 || ![setter hasPrefix:@"set"] || ![setter hasSuffix:@":"]) { return nil;}
    
    NSRange range = NSMakeRange(3, setter.length-4);
    NSString *getter = [setter substringWithRange:range];
    NSString *firstString = [[getter substringToIndex:1] lowercaseString];
    return  [getter stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:firstString];
}


@end

• 1.验证这个传入景来的keyPath 是否存在setter方法
• 2.生成一个动态子类 Class newClass = [self createChildClassWithKeyPath:keyPath];
  • 2.1根据原类的名字拼接字符串生成新子类的名字字符串
  • 2.2判断是否重复
  • 2.3申请类，注册类
  • 2.4添加class方法。添加setter方法
  • setter方法中需要将设置好的新值发送给观察者所以在要提前保存好观察者的信息。保存到数组中

static void lg_setter(id self,SEL _cmd,id newValue){
    NSLog(@"来了:%@",newValue);
    // 4: 消息转发 : 转发给父类
    // 改变父类的值 --- 可以强制类型转换
    NSString *keyPath = getterForSetter(NSStringFromSelector(_cmd));
    id oldValue       = [self valueForKey:keyPath];
    
    void (*lg_msgSendSuper)(void *,SEL , id) = (void *)objc_msgSendSuper;
    // void /* struct objc_super *super, SEL op, ... */
    struct objc_super superStruct = {
        .receiver = self,
        .super_class = class_getSuperclass(object_getClass(self)),
    };
    //objc_msgSendSuper(&superStruct,_cmd,newValue)
    lg_msgSendSuper(&superStruct,_cmd,newValue);
    // 1: 拿到观察者
    NSMutableArray *observerArr = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey));
    - 这里需要将setter方法的消息发送给观察者
    for (LGKVOInfo *info in observerArr) {
        if ([info.keyPath isEqualToString:keyPath]) {
            dispatch_async(dispatch_get_global_queue(0, 0), ^{
                NSMutableDictionary<NSKeyValueChangeKey,id> *change = [NSMutableDictionary dictionaryWithCapacity:1];
                // 对新旧值进行处理
                if (info.options & LGKeyValueObservingOptionNew) {
                    [change setObject:newValue forKey:NSKeyValueChangeNewKey];
                }
                if (info.options & LGKeyValueObservingOptionOld) {
                    [change setObject:@"" forKey:NSKeyValueChangeOldKey];
                    if (oldValue) {
                        [change setObject:oldValue forKey:NSKeyValueChangeOldKey];
                    }
                }
                // 2: 消息发送给观察者
                SEL observerSEL = @selector(lg_observeValueForKeyPath:ofObject:change:context:);
                objc_msgSend(info.observer,observerSEL,keyPath,self,change,NULL);
            });
        }
    }
    
}

Class lg_class(id self,SEL _cmd){
    return class_getSuperclass(object_getClass(self));
}

• 3.isa的指向 : LGKVONotifying_LGPerson     object_setClass(self, newClass);
• 4: 保存观察者信息     LGKVOInfo *info = [[LGKVOInfo alloc] initWitObserver:observer forKeyPath:keyPath options:options];
• 5.移除循环遍历判断删除

- (void)lg_removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath{
    
    NSMutableArray *observerArr = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey));
    if (observerArr.count<=0) {
        return;
    }
    
    for (LGKVOInfo *info in observerArr) {
        if ([info.keyPath isEqualToString:keyPath]) {
            [observerArr removeObject:info];
            objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey), observerArr, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
            break;
        }
    }

    if (observerArr.count<=0) {
        // 指回给父类
        Class superClass = [self class];
        object_setClass(self, superClass);
    }
}

拓展函数式编程

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

typedef void(^LGKVOBlock)(id observer,NSString *keyPath,id oldValue,id newValue);

@interface NSObject (LGKVO)

- (void)lg_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath block:(LGKVOBlock)block;

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

@end

NS_ASSUME_NONNULL_END

//
//  NSObject+LGKVO.m
//  004---自定义函数式KVO
//
//  Created by cooci on 2019/1/5.
//  Copyright © 2019 cooci. All rights reserved.
//

#import "NSObject+LGKVO.h"
#import <objc/message.h>

static NSString *const kLGKVOPrefix = @"LGKVONotifying_";
static NSString *const kLGKVOAssiociateKey = @"kLGKVO_AssiociateKey";

@interface LGInfo : NSObject
@property (nonatomic, weak) NSObject  *observer;
@property (nonatomic, copy) NSString    *keyPath;
@property (nonatomic, copy) LGKVOBlock  handleBlock;
@end

@implementation LGInfo

- (instancetype)initWitObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath handleBlock:(LGKVOBlock)block{
    if (self=[super init]) {
        _observer = observer;
        _keyPath  = keyPath;
        _handleBlock = block;
    }
    return self;
}
@end

@implementation NSObject (LGKVO)

- (void)lg_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath block:(LGKVOBlock)block{
    
    // 1: 验证是否存在setter方法 : 不让实例进来
    [self judgeSetterMethodFromKeyPath:keyPath];
    // 2: 动态生成子类
    Class newClass = [self createChildClassWithKeyPath:keyPath];
    // 3: isa的指向 : LGKVONotifying_LGPerson
    object_setClass(self, newClass);
    // 4: 保存信息
    LGInfo *info = [[LGInfo alloc] initWitObserver:observer forKeyPath:keyPath handleBlock:block];
    NSMutableArray *mArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey));
    if (!mArray) {
        mArray = [NSMutableArray arrayWithCapacity:1];
        objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey), mArray, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    [mArray addObject:info];
}

- (void)lg_removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath{
    
    NSMutableArray *observerArr = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey));
    if (observerArr.count<=0) {
        return;
    }
    
    for (LGInfo *info in observerArr) {
        if ([info.keyPath isEqualToString:keyPath]) {
            [observerArr removeObject:info];
            objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey), observerArr, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
            break;
        }
    }
    
    if (observerArr.count<=0) {
        // 指回给父类
        Class superClass = [self class];
        object_setClass(self, superClass);
    }
}

#pragma mark - 验证是否存在setter方法
- (void)judgeSetterMethodFromKeyPath:(NSString *)keyPath{
    Class superClass    = object_getClass(self);
    SEL setterSeletor   = NSSelectorFromString(setterForGetter(keyPath));
    Method setterMethod = class_getInstanceMethod(superClass, setterSeletor);
    if (!setterMethod) {
        @throw [NSException exceptionWithName:NSInvalidArgumentException reason:[NSString stringWithFormat:@"老铁没有当前%@的setter",keyPath] userInfo:nil];
    }
}

#pragma mark -
- (Class)createChildClassWithKeyPath:(NSString *)keyPath{
    
    NSString *oldClassName = NSStringFromClass([self class]);
    NSString *newClassName = [NSString stringWithFormat:@"%@%@",kLGKVOPrefix,oldClassName];
    Class newClass = NSClassFromString(newClassName);
    // 防止重复创建生成新类
    if (newClass) return newClass;
    /**
     * 如果内存不存在,创建生成
     * 参数一: 父类
     * 参数二: 新类的名字
     * 参数三: 新类的开辟的额外空间
     */
    // 2.1 : 申请类
    newClass = objc_allocateClassPair([self class], newClassName.UTF8String, 0);
    // 2.2 : 注册类
    objc_registerClassPair(newClass);
    // 2.3.1 : 添加class : class的指向是LGPerson
    SEL classSEL = NSSelectorFromString(@"class");
    Method classMethod = class_getInstanceMethod([self class], classSEL);
    const char *classTypes = method_getTypeEncoding(classMethod);
    class_addMethod(newClass, classSEL, (IMP)lg_class, classTypes);
    // 2.3.2 : 添加setter
    SEL setterSEL = NSSelectorFromString(setterForGetter(keyPath));
    Method setterMethod = class_getInstanceMethod([self class], setterSEL);
    const char *setterTypes = method_getTypeEncoding(setterMethod);
    class_addMethod(newClass, setterSEL, (IMP)lg_setter, setterTypes);
    return newClass;
}

static void lg_setter(id self,SEL _cmd,id newValue){
    NSLog(@"来了:%@",newValue);
    NSString *keyPath = getterForSetter(NSStringFromSelector(_cmd));
    id oldValue = [self valueForKey:keyPath];
    // 4: 消息转发 : 转发给父类
    // 改变父类的值 --- 可以强制类型转换
    void (*lg_msgSendSuper)(void *,SEL , id) = (void *)objc_msgSendSuper;
    // void /* struct objc_super *super, SEL op, ... */
    struct objc_super superStruct = {
        .receiver = self,
        .super_class = class_getSuperclass(object_getClass(self)),
    };
    //objc_msgSendSuper(&superStruct,_cmd,newValue)
    lg_msgSendSuper(&superStruct,_cmd,newValue);
    
    // 5: 信息数据回调
    NSMutableArray *mArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kLGKVOAssiociateKey));
    
    for (LGInfo *info in mArray) {
        if ([info.keyPath isEqualToString:keyPath] && info.handleBlock) {
            info.handleBlock(info.observer, keyPath, oldValue, newValue);
        }
    }
}

Class lg_class(id self,SEL _cmd){
    return class_getSuperclass(object_getClass(self));
}

#pragma mark - 从get方法获取set方法的名称 key ===>>> setKey:
static NSString *setterForGetter(NSString *getter){
    
    if (getter.length <= 0) { return nil;}
    
    NSString *firstString = [[getter substringToIndex:1] uppercaseString];
    NSString *leaveString = [getter substringFromIndex:1];
    
    return [NSString stringWithFormat:@"set%@%@:",firstString,leaveString];
}

#pragma mark - 从set方法获取getter方法的名称 set<Key>:===> key
static NSString *getterForSetter(NSString *setter){
    
    if (setter.length <= 0 || ![setter hasPrefix:@"set"] || ![setter hasSuffix:@":"]) { return nil;}
    
    NSRange range = NSMakeRange(3, setter.length-4);
    NSString *getter = [setter substringWithRange:range];
    NSString *firstString = [[getter substringToIndex:1] lowercaseString];
    return  [getter stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:firstString];
}


@end

KVC

文档地址

• KVC的全称是Key-Value Coding，俗称“键值编码”，可以通过一个key来访问某个属性
• 常见的API有

  • (void)setValue:(id)value forKeyPath:(NSString *)keyPath;

  • (void)setValue:(id)value forKey:(NSString *)key;

  • (id)valueForKeyPath:(NSString *)keyPath;

  • (id)valueForKey:(NSString *)key;

• setValue:forKey: 的原理
  
• 调用顺序
  • 1.查找调用setKey:方法,没有则查找调用_setKey:找到了就传值调用方法没有则调用第三步setIsKey
  • 2.三个个方法都没有就查找 accessInstanceVariableDirecity 看返回值是Yes还是No
  • 3.Yes就按顺序查找是否有 _key _iskey key isKey 这些成员变量 有就给他们赋值
  • 4.No 或者 没有对应的成员变量就报错说没有这样的成员变量

LGPerson *person = [[LGPerson alloc] init];

    // 1: KVC - 设置值的过程 setValue 分析调用过程
    // [person setValue:@"LG_Cooci" forKey:@"name"];
//     NSLog(@"%@-%@-%@-%@",person->_name,person->_isName,person->name,person->isName);
//     NSLog(@"%@-%@-%@",person->_isName,person->name,person->isName);
//     NSLog(@"%@-%@",person->name,person->isName);
//     NSLog(@"%@",person->isName);

• valueForKey:的原理
• 调用循序 类似同上
  • 1.查找调用getKey:、key:、isKey、_key、找到了就传值调用方法
  • 2.二个方法都没有就查找 accessInstanceVariableDirecity 看返回值是Yes还是No
  • 3.Yes就按顺序查找是否有 _key _iskey key isKey 这些成员变量 有就取值
  • 4.No 或者 没有对应的成员变量就报错说没有这样的成员变量

    // setter - getter  - KVC 设值 和 取值的流程
    // 2: KVC - 取值的过程
    // _name
//    person->_name = @"_name";
//    person->_isName = @"_isName";
    person->name = @"name";
//    person->isName = @"isName";
    NSLog(@"取值:%@",[person valueForKey:@"name"]);