ios - kvo观察者示例

首先创建Person分类



#import <Foundation/Foundation.h>

@interface Person : NSObject

@property (nonatomic, copy) NSString *name;

@property (nonatomic, assign) float height;

@end

.m中不做任何事情
控制器.m中



#import "ViewController.h"

#import "Person.h"

@interface ViewController ()

@property (nonatomic, strong) Person *per;

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    Person * per = [Person new];

    per.name = @"zhangsan";

    per.height = 1.2;

    self.per = per;

    // kvo 为per.name添加观察者

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

    // kvo 为per.height添加观察者

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

}

只要监听的属性name 和 height的值发生了改变就会触发下面的方法



/** 添加观察者必须要实现的方法 */

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

    /** 打印新老值 */

    // 从打印结果看 分别打印出了 name 与 height的新老值

    NSLog(@"old : %@  new : %@",[change objectForKey:@"old"],[change objectForKey:@"new"]);

//    NSLog(@"keypath :  %@",keyPath);

//    NSLog(@"change : %@",change);

}

由于对person.name 以及height的属性都做了监听,只要触摸后属性的值发生改变就做得到通知触发通知方法 -(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context 则可以在其内部做你想要做的事



/** 触摸改变per.name属性值 */

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{

    self.per.name = @"helloworld";

    self.per.height = 3.3;

}

一定要记得移除



/** 移除 */

-(void)dealloc{

    [self.per removeObserver:self forKeyPath:@"name" context:nil];

    [self.per removeObserver:self forKeyPath:@"height" context:nil];

}

- (void)didReceiveMemoryWarning {

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}

@end

注意点:

为某个对象的某个属性添加观察者,最后一定要移除,否则可能会崩溃

实现方法-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context则只要监听的属性发生改变就会触发.

巴特西

ios - kvo观察者示例

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