KVO(Key-Value-Observe)
KVO簡單點說就是觀察數據的變化,數據變化 執行其它方法
1.KVO是一種輕量級的觀察者模式
2.用來觀察Value的變化
3.觀察者模式可以極大程度的解耦合(降低耦合度)
Car.h
@property (nonatomic, copy) NSString *type;
Person.h
@property (nonatomic, copy) NSString *name;
@property (nonatomic, strong) Car *car;
- (instancetype)initWithName:(NSString *)name car:(Car *)car;
Person.m
@implementation Person{
NSString *sex;
}
+ (BOOL)accessInstanceVariablesDirctly{
return NO;
}
- (instancetype)initWithName:(NSString *)name car:(Car *)car{
self = [super init];
if(self){
_name = [name copy];
//self.name
_car = car;
}
return self;
}
2.當觀察者的屬性發生值得變化時,就會回調該方法,這個方法要寫在觀察者所在的類中
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
NSLog(@"keyPath:%@",keyPath);
NSLog(@"object:%@",object);
//object爲監聽的對象
NSLog(@"change:%@",change);
}
main.m
Car *car = [[Car alloc]init];
car.type = @"別克";
Person *person = [[Person alloc]init];
person設置爲car對象的觀察者,用來觀察屬性的變化
添加觀察者
NSKeyValueObservingOptionNew //觀察屬性的新值
NSKeyValueObservingOptionOld
//觀察屬性的舊值
New|Initial
觀察初始化的值
[car addObserver:person forKeyPath:@"type" option:NSKeyValueObservingOptionNew
| NSKeyValueObservingOptionInitial context:NULL];
car.type = @"寶馬";
car.type = @"自行車";
移除觀察者,不移除崩潰
[car removeObserver: person forKeyPath:@"type"];
Person *person1 = [[Person alloc]init];
[person setValue:car forKey:@"car"];
person1.car.type
//通過KVC賦值
[person setValue:@"大奔" forKeyPath:@"car.type"];