KVO的简单用法

//  Created by wjn on 15/9/30.

//  Copyright © 2015年 wlm. All rights reserved.

//

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, retain) NSString *string;

@end

@implementation ViewController

- (void)dealloc {

    

    // 切记一定要在完成之后移除掉 - ARC一样

    [self removeObserver:self forKeyPath:@"string"];

    

    [super dealloc];

}

- (void)viewDidLoad {

    [super viewDidLoad];

    // Do any additional setup after loading the view, typically from a nib.

    

    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];

    button.frame = CGRectMake(0, 20, self.view.frame.size.width, 40);

    [button setTitle:@"KVO" forState:UIControlStateNormal];

    [button setBackgroundColor:[UIColor greenColor]];

    

    [button addTarget:self action:@selector(buttonDidPress:) forControlEvents:UIControlEventTouchUpInside];

    

    [self.view addSubview:button];

    

    // KVO 一个类监听自己的属性（成员变量）的变化

    // 参数1：观察者

    // 参数2：要观察的对象

    // 参数3：一旦发生改变，观察的结果是取新值还是旧值

    // 参数4：一旦发生改变，可以传递的内容

    

    [self addObserver:self forKeyPath:@"string" options:NSKeyValueObservingOptionNew context:@"BOOM"];

}

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

    // 系统的方法

    // 当观察到的属性改变之后，自动调用这个方法

    NSLog(@"%@", keyPath);

    NSLog(@"%@", object);

    NSLog(@"%@", change);

    NSLog(@"%@", context);

}

//-(NSMutableArray *)mutableArray {

//    if (!_mutableArray) {

//        self.mutableArray = [NSMutableArray arrayWithObject:@"a"];

//    }

//    return _mutableArray;

//}

- (void)buttonDidPress:(UIButton *)sender {

//    [self.mutableArray addObject:@"a"];

    [self setValue:@"aa" forKey:@"string"];

}

- (void)didReceiveMemoryWarning {

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}

@end