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

-(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"];}

//// 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