IOS KVO

KVO  Key-Value Observing  它提供一种机制，当指定的对象的属性被修改后，则观察者就会接受到通知!!

观察者可以是对象本身，也可以是其他的类对象!!

使用步骤:

1.注册观察对象的属性!

2.实现观察触发的回调方法!

3.在dealloc中移除观察

 

下面贴一段测试代码:

创建一个Person类

//.h文件
#import <Foundation/Foundation.h>

@interface Person : NSObject
@property(nonatomic,copy)NSString *name;
@property(nonatomic,assign)float height;
@property(nonatomic,strong)NSMutableArray *array;
+(Person *)personWithName:(NSString *)aName height:(float)height;
@end

//.m 文件
#import "Person.h"
@implementation Person
+(Person *)personWithName:(NSString *)aName height:(float)height
{
    Person *per = [[Person alloc]init];
    per.name = aName;
    per.height = height;
    per.array = [NSMutableArray arrayWithArray:@[@"zzzXXXzzz"]];
    return per;
}
@end

//在需要用的控制器或者类中  注册观察
_person = [Person personWithName:@"AAA" height:179.5];

[_person addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];
[_person addObserver:self forKeyPath:@"height" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];
[_person addObserver:self forKeyPath:@"array" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];

//改变观察的属性的值
 
_person.name = @"BBB";//触发一次观察方法
    _person.name = @"CCC";//触发一次观察方法
    _person.height = 185;//触发一次观察方法
    
    //这种向数组中添加删除数据不会触发观察方法
    [_person.array addObject:@"123"];
    [_person.array addObject:@"456"];
    [_person.array removeObject:@"123"];
    
    //重新给数组赋值,可以触发观察者方法
    _person.array = [@[@"creat",@"a",@"new",@"array"] mutableCopy];

//在注册观察的类中  实现这个观察回调方法

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"name"])
    {
        NSLog(@"改变前的值:%@  ---  改变后的值:%@",[change objectForKey:@"old"],[change objectForKey:@"new"]);
    }
    if ([keyPath isEqualToString:@"height"])
    {
        //you code
        NSLog(@"改变前的值:%@  ---  改变后的值:%@",[change objectForKey:@"old"],[change objectForKey:@"new"]);
    }
    if ([keyPath isEqualToString:@"array"])
    {
        NSLog(@"改变前的值:%@  ---  改变后的值:%@",[change objectForKey:@"old"],[change objectForKey:@"new"]);
    }
}

//移除观察
-(void)dealloc
{
    [_person removeObserver:self forKeyPath:@"name"];
    [_person removeObserver:self forKeyPath:@"height"];
    [_person removeObserver:self forKeyPath:@"array"];
}

文章到这已经结束啦，希望对路过的朋友有所帮助!!!