IOS 中的KVO模式 观察者模式

/
//  KvoObject.h
//  KVO
//
//  Created by lin kang on 16/6/7.
//  Copyright © 2016年 lin kang. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface KvoObject : NSObject

@property (nonatomic,retain) NSString *changeStr;

@end

//
//  KvoObject.m
//  KVO
//
//  Created by lin kang on 16/6/7.
//  Copyright © 2016年 lin kang. All rights reserved.
//

#import "KvoObject.h"

@implementation KvoObject
@synthesize changeStr = _changeStr;

+(BOOL)automaticallyNotifiesObserversForKey:(NSString *)key{
//进行手动调用观察者模式 返回NO
if ([key isEqualToString:@"changeStr"]) {
return NO;
}else{
return [super automaticallyNotifiesObserversForKey:key];
}
}

-(NSString *)changeStr{
if (_changeStr == nil) {
_changeStr = @"KVO模式";
}
return _changeStr;
}

-(void)setChangeStr:(NSString *)changeStr{
_changeStr = changeStr;
//要进行触发观察者模式，需触发这两个方法
[self willChangeValueForKey:@"changeStr"];
[self didChangeValueForKey:@"changeStr"];
}
@end

//
//  ViewController.m
//  KVO
//
//  Created by lin kang on 16/6/7.
//  Copyright © 2016年 lin kang. All rights reserved.
//

#import "ViewController.h"
#import "AppDelegate.h"
#import "ViewController1.h"

@interface ViewController ()
{
AppDelegate *_appDelegate;
UILabel *_lable;
}
@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
_appDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

// Do any additional setup after loading the view, typically from a nib.
UILabel *lb = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 200, 21)];
lb.center =self.view.center;
lb.text = _appDelegate.kvoObject.changeStr;
lb.backgroundColor = [UIColor blueColor];
_lable = lb;
[self.view addSubview:lb];

UIButton *bt = [UIButton buttonWithType:UIButtonTypeCustom];
[bt setTitle:@"点我" forState:UIControlStateNormal];
[bt setBackgroundColor:[UIColor redColor]];
[bt setFrame:CGRectMake(100, 300, 60, 44)];
[self.view addSubview:bt];
[bt addTarget:self action:@selector(btc:) forControlEvents:UIControlEventTouchUpInside];

//注册自己为观察者
[_appDelegate.kvoObject addObserver:self forKeyPath:@"changeStr" options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:nil];
}

//接受观察通知
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
NSLog(@"change:%@",change);
NSString *newStr = [change objectForKey:@"new"];
_lable.text = newStr;
//    [self.view setNeedsDisplay];
}

-(void)btc:(UIButton *)sender{
ViewController1 *vc1 = [[ViewController1 alloc] init];
[self.navigationController pushViewController:vc1 animated:YES];
}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

@end

//
//  ViewController1.m
//  KVO
//
//  Created by lin kang on 16/6/7.
//  Copyright © 2016年 lin kang. All rights reserved.
//

#import "ViewController1.h"
#import "AppDelegate.h"

@interface ViewController1 ()
{
AppDelegate *_appDelegate;
UILabel     *_lable;
}
@end

@implementation ViewController1

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
_appDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
// Do any additional setup after loading the view, typically from a nib.
UILabel *lb = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 200, 21)];
lb.center =self.view.center;
lb.text = _appDelegate.kvoObject.changeStr;
lb.backgroundColor = [UIColor blueColor];
_lable = lb;
[self.view addSubview:lb];

UIButton *bt = [UIButton buttonWithType:UIButtonTypeCustom];
[bt setTitle:@"改变对象" forState:UIControlStateNormal];
[bt setBackgroundColor:[UIColor redColor]];
[bt setFrame:CGRectMake(100, 300, 60, 44)];
[self.view addSubview:bt];
[bt addTarget:self action:@selector(changeing:) forControlEvents:UIControlEventTouchUpInside];
//注册自己为观察者
[_appDelegate.kvoObject addObserver:self forKeyPath:@"changeStr" options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:nil];
}

//改变对象
-(void)changeing:(UIButton *)sender{
_appDelegate.kvoObject.changeStr = @"我变了，操！";
}

//接收通知
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
NSLog(@"change:%@",change);
NSString *newStr = [change objectForKey:@"new"];
_lable.text = newStr;
//    [self.view setNeedsDisplay];
}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
// Get the new view controller using [segue destinationViewController].
// Pass the selected object to the new view controller.
}
*/

@end