KVO 是 OC
觀察者設(shè)計(jì)模式的一種
KVO 的實(shí)現(xiàn)依賴于 OC 強(qiáng)大的 Runtime
KVO是Cocoa提供的一種基于KVC的機(jī)制
允許一個(gè)對(duì)象(A)去監(jiān)聽(tīng)另一個(gè)對(duì)象(B)的某個(gè)屬性幔烛，當(dāng)該屬性改變時(shí)捏雌，系統(tǒng)會(huì)通知監(jiān)聽(tīng)的對(duì)象(A)
一、KVO的基本使用流程有三步
1.添加監(jiān)聽(tīng)
- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullablevoid *)context;（系統(tǒng)還有其他添加方法）
2.接收通知
- (void)observeValueForKeyPath:(nullableNSString *)keyPath ofObject:(nullableid)object change:(nullableNSDictionary<NSKeyValueChangeKey,id> *)change context:(nullablevoid *)context
3.移除監(jiān)聽(tīng)
- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath context:(nullable void *)context （系統(tǒng)還有其他移除方法）
KVO的觸發(fā)
@property (nonatomic,strong) Person *p;
Person *p = [Person new];
_p = p;
[p addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew context:nil];
#pragma mark - 點(diǎn)擊改變 name 的屬性
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
static int i = 0;//加上static的目的是每次進(jìn)來(lái)改變i的值峡捡。就不會(huì)重新初始化了
i++;
_p.name = [NSString stringWithFormat:@"%d",i];
}
#只要一點(diǎn)擊屏幕就會(huì)導(dǎo)致_p.name改變，那么就會(huì)觸發(fā)KVO
KVO原理：通過(guò)實(shí)現(xiàn)自定義的KVO來(lái)理解
簡(jiǎn)單概括：
KVO系統(tǒng)的處理是通過(guò)運(yùn)行時(shí)孟岛，替換了對(duì)象的isa指針對(duì)象凤巨，并重寫(xiě)了set等方法
1、創(chuàng)建一個(gè)Person類(lèi)
2男摧、寫(xiě)一個(gè)NSObject+RRKVO.h分類(lèi)
1. Person
// Person.h
#import <Foundation/Foundation.h>
@interface Person : NSObject
/** name */
@property (nonatomic,copy) NSString *name;
@end
#import "Person.h"
@implementation Person
//不影響重寫(xiě)set方法
-(void)setName:(NSString *)name{
_name = [NSString stringWithFormat:@"在不影響重寫(xiě)set方法的情況下加上這句%@",name];
}
@end
2.參照系統(tǒng)KVO
// NSObject+RRKVO.h
#import <Foundation/Foundation.h>
@interface NSObject (RRKVO)
- (void)rr_addObserver:(NSObject *_Nullable)observer forKeyPath:(NSString *_Nullable)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;
@end
// NSObject+RRKVO.m
#import "NSObject+RRKVO.h"
#import <objc/message.h>
@implementation NSObject (RRKVO)
//self 是 被觀察者 （Person）
//observer 是 觀察者
- (void)rr_addObserver:(NSObject *_Nullable)observer forKeyPath:(NSString *_Nullable)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context{
/*
1蔬墩、自定義子類(lèi)對(duì)象
2、重寫(xiě)setName:方法耗拓，調(diào)用super的拇颅，通知觀察者
3、修改當(dāng)前對(duì)象的isa指針乔询，只想自定義的子類(lèi)
*/
//1樟插、動(dòng)態(tài)生成一個(gè)類(lèi)
//1.1創(chuàng)建self的子類(lèi)
NSString *oldClassName = NSStringFromClass([self class]);
NSString *newClassName = [@"rrKVO_" stringByAppendingString:oldClassName];
const char *newName = [newClassName UTF8String];
//創(chuàng)建一個(gè)類(lèi)的class
Class myClass = objc_allocateClassPair([self class], newName, 0);
//注冊(cè)類(lèi)
//就可以加入到內(nèi)存中了 就可以用來(lái)alloc init了
objc_registerClassPair(myClass);
//2.添加set方法
class_addMethod(myClass, @selector(setName:), (IMP)setName, "v@:@");//查看官方文檔可得 cmd
//3.修改isa指針
object_setClass(self, myClass);
//4.保存觀察者對(duì)象
objc_setAssociatedObject(self, @"objc", observer, OBJC_ASSOCIATION_RETAIN_NONATOMIC);//相當(dāng)于給self動(dòng)態(tài)的創(chuàng)建了一個(gè)屬性
}
#pragma mark - 1.調(diào)用supper的set方法 2.通知外界
void setName(id self,SEL _cmd,NSString *newName){
NSLog(@"運(yùn)行這里");
//調(diào)用父類(lèi)的
//保存子類(lèi)類(lèi)型
id class = [self class];
//改變self的isa指針
object_setClass(self, class_getSuperclass(class));
//調(diào)用父類(lèi)的set方法
objc_msgSend(self, @selector(setName:),newName);
NSLog(@"修改完畢");
//拿到觀察者
id objc = objc_getAssociatedObject(self, @"objc");
//通知觀察者
objc_msgSend(objc, @selector(observeValueForKeyPath:ofObject:change:context:),self,@"name",nil,nil);
//改回子類(lèi)類(lèi)型
object_setClass(self, class);
}
@end
3.應(yīng)用
#import "ViewController.h"
#import "NSObject+RRKVO.h"
#import "Person.h"
@interface ViewController ()
/** person */
@property (nonatomic,strong) Person *p;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
Person *p = [Person new];
_p = p;
//使用自定義的KVO來(lái)監(jiān)聽(tīng)！Person的name屬性
NSLog(@"改之前%@",[p class]);
[p rr_addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew context:nil];
NSLog(@"改之后%@",[p class]);
}
#pragma mark - 監(jiān)聽(tīng)到就來(lái)了
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{
NSLog(@"來(lái)到這竿刁，%@",_p.name);//這里會(huì)走重寫(xiě)的set方法
}
#pragma mark - 點(diǎn)擊改變 name 的屬性
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
static int i = 0;//加上static的目的是每次進(jìn)來(lái)改變i的值黄锤。就不會(huì)重新初始化了
i++;
_p.name = [NSString stringWithFormat:@"%d",i];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
NSLog
2017-06-21 10:57:05.093 004-自己寫(xiě)KVO[7808:2159755] 改之前Person
2017-06-21 10:57:05.093 004-自己寫(xiě)KVO[7808:2159755] 改之后rrKVO_Person
點(diǎn)擊屏幕之后NSLog
2017-06-21 10:58:17.213 004-自己寫(xiě)KVO[7808:2159755] 運(yùn)行這里
2017-06-21 10:58:17.213 004-自己寫(xiě)KVO[7808:2159755] 修改完畢
2017-06-21 10:58:17.214 004-自己寫(xiě)KVO[7808:2159755] 來(lái)到這，在不影響重寫(xiě)set方法的情況下加上這句1
