KVO详解

- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;

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

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

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.personModel = [[BYPersonModel alloc] init];
    [self.personModel setName:@"Tony Qiu"];
    
    /// 添加监听
    /// options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld 监听新值和旧值,若不传则在监听方法中，无法捕获变化的值
    [self.personModel addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
    [self.personModel addObserver:self forKeyPath:@"age" options:NSKeyValueObservingOptionNew context:nil];
    
    /// 改变属性值 就能在监听中捕获变化
	[self.personModel setName:@"Peng YuYan"];
    [self.personModel setAge:28];
}

/// 在非正式协议里监听对象变化
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{
    NSLog(@"%@", change);
}

/// 移除监听
- (void)dealloc {
    [self.personModel removeObserver:self forKeyPath:@"name"];
    [self.personModel removeObserver:self forKeyPath:@"age"];
}

NSLog(@"%@", object_getClass(self.personModel));
[self.personModel addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
NSLog(@"%@", object_getClass(self.personModel));

/// 打印方法
- (void)methodsByClass:(Class)cls{
    NSLog(@"%@ methods:", cls);
    unsigned int count;
    Method *methods = class_copyMethodList(cls, &count);
    
    for (NSInteger index = 0; index < count; index++) {
        Method method = methods[index];
        
        NSString *methodStr = NSStringFromSelector(method_getName(method));
        NSLog(@"%@", methodStr);
    }
    
    free(methods);
}

/// 打印属性
- (void)ivarsByClass:(Class)cls{
    NSLog(@"%@ ivars:", cls);
    unsigned int count;
    Ivar *ivars = class_copyIvarList(cls, &count);
    
    for (NSInteger index = 0; index < count; index++) {
        Ivar ivar = ivars[index];
        NSString *ivarName = [NSString stringWithUTF8String:ivar_getName(ivar)];  //获取成员变量的名字
        NSString *ivarType = [NSString stringWithUTF8String:ivar_getTypeEncoding(ivar)]; //获取成员变量的数据类型
        NSLog(@"%@ %@", ivarName, ivarType);
    }
    
    free(ivars);

}

- (void)creatClass {
	/// 创建类
	Class customClass = objc_allocateClassPair([NSObject class], "BYCustomClass", 0);
	/// 添加实例变量和方法
	class_addIvar(customClass, "age", sizeof(int), 0, "i");
	class_addIvar(customClass, "name", sizeof(id), log2(sizeof(id)), @encode(id));
	/// 添加方法，`V@:`表示方法的参数和返回值
	class_addMethod(customClass, @selector(gohome), (IMP)gohome, "V@:");
	/// 注册到运行时环境(注意：注册后无法再添加方法和实例变量)
	objc_registerClassPair(customClass);
}

void gohome(id self, SEL _cmd)
{
    NSLog(@"回家了");
}

- (void)gohome {
}

@interface NSObject (kvo)
/// 添加一个KVO方法
- (void)by_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;
@end

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

@implementation NSObject (kvo)

- (void)by_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context{
    //动态添加一个类
    NSString *originClassName = NSStringFromClass([self class]);
    
    NSString *newClassName = [@"BY_NSKVONotifying_" stringByAppendingString:originClassName];
    
    // 继承自当前类，创建一个子类，类名模仿KVO底层命名 BY_NSKVONotifying_+类名的形式
    Class kvoClass = objc_allocateClassPair([self class], [newClassName UTF8String], 0);
    
    // 添加setter方法 这里我们只监听 name，手动添加setName方法。
    // v@:@：v 对应setName方法的返回值void，@: 表示方法本身，@ 表示参数是个对象
    class_addMethod(kvoClass, @selector(setName:), (IMP)setName, "v@:@");
    
    //注册新添加的这个类
    objc_registerClassPair(kvoClass);
    
    // 修改isa指针，由 personModel 指向我们创建的 BY_NSKVONotifying_BYPrsonModel 对象实现替换
    object_setClass(self, kvoClass);
    
    // 保存观察者属性到当前类中
    objc_setAssociatedObject(self, (__bridge const void *)@"observer", observer, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

#pragma mark - 重写父类方法

void setName(id self, SEL _cmd, NSString *name) {
    
    // 保存当前KVO的类
    Class kvoClass = [self class];
    
    // 将self的isa指针指向父类BYPersonModel，调用父类setter方法
    object_setClass(self, class_getSuperclass([self class]));
    objc_msgSend(self, @selector(setName:), name);
    
    // 获取BY_NSKVONotifying_BYPrsonModel观察者
    id objc = objc_getAssociatedObject(self, (__bridge const void *)@"observer");
    // 通知观察者，执行通知方法
    NSDictionary<NSKeyValueChangeKey,id> *change = @{@"kind": @1, @"new": name};
    objc_msgSend(objc, @selector(observeValueForKeyPath:ofObject:change:context:), @"name", self, change, nil);
    
    // 将指针重新指向 BY_NSKVONotifying_BYPrsonModel
    object_setClass(self, kvoClass);
}


@end

self.personModel = [[BYPersonModel alloc] init];
[self.personModel setName:@"Tony Qiu"];
    
NSLog(@"%@", object_getClass(self.personModel));
[self.personModel by_addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
NSLog(@"%@", object_getClass(self.personModel));