iOS 监听回调机制KVO

监听某个对象，如果这个对象的数据发生变化，会发送给监听者从而触发回调函数

    [self.bean addObserver:self forKeyPath:@"data" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];

这个就是注册监听，这个@“data”作为标识符方便回调函数辨认

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

{

    if([keyPath isEqualToString:@"data"])

    {

        self.label.text = [self.bean valueForKey:@"data"];

    }

}

这个就是回调函数，分辨是哪个对象发生变化，然后给与相应的处理

-(void)viewWillDisappear:(BOOL)animated{

    [self.bean removeObserver:self forKeyPath:@"data"];

}

既然有注册监听还记得解除监听

以下是完整例子代码

//
// ViewController.m
// First
//
// Created by shanreal-iOS on 17/10/16.
// Copyright © 2017年 shanreal.LongZhenHao. All rights reserved.
//

#import "ViewController.h"
#import "TestBean.h"
@interface ViewController ()
@property(nonatomic,strong)UILabel* label;
@property(nonatomic,strong)UIButton* btn;
@property(nonatomic,strong)TestBean* bean;
@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.

self.bean = [[TestBean alloc]init];
[self.bean setValue:@"1" forKey:@"data"];

self.label = [[UILabel alloc]initWithFrame:CGRectMake(10, 30, 100, 30)];
self.label.textColor = [UIColor blackColor];
self.label.text = [self.bean valueForKey:@"data"];
[self.view addSubview:self.label];

self.btn = [[UIButton alloc] initWithFrame:CGRectMake(10, 100, 200, 30)];
[self.btn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[self.btn setTitle:@"chanage data" forState:UIControlStateNormal];
[self.btn addTarget:self action:@selector(clickAction) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:self.btn];

}
-(void)viewWillAppear:(BOOL)animated{
[self.bean addObserver:self forKeyPath:@"data" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];

}

-(void)clickAction{
int data = [[self.bean valueForKey:@"data"] intValue]+1;
self.bean.data = [NSString stringWithFormat:@"%d",data];
}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
if([keyPath isEqualToString:@"data"])
{
self.label.text = [self.bean valueForKey:@"data"];
}
}
-(void)viewWillDisappear:(BOOL)animated{
[self.bean removeObserver:self forKeyPath:@"data"];
}

@end

#import <Foundation/Foundation.h>

@interface TestBean : NSObject{
NSString* data;
}
@property(nonatomic,assign)int id;
@property(nonatomic,strong)NSString* data;
@end

#import "TestBean.h"

@implementation TestBean

@end