監聽某個對象，如果這個對象的數據發生變化，會發送給監聽者從而觸發回調函數
[self.bean addObserver:self forKeyPath:@"data" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];
這個就是注冊監聽，這個@“data”作為標識符方便回調函數辨認
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{ if([keyPath isEqualToString:@"data"]) { self.label.text = [self.bean valueForKey:@"data"]; }}這個就是回調函數，分辨是哪個對象發生變化，然后給與相應的處理
-(void)viewWillDisappear:(BOOL)animated{ [self.bean removeObserver:self forKeyPath:@"data"];}既然有注冊監聽還記得解除監聽
以下是完整例子代碼
//// 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以上這篇iOS 監聽回調機制KVO實例就是小編分享給大家的全部內容了，希望能給大家一個參考，也希望大家多多支持武林網。
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