谈谈kvc和kvo

kvc(Key Value Coding)用来给对象的属性或成员变量赋值，或者读取对象属性或成员变量的值，调用setValue:forKey:方法给对象的属性或成员变量赋值，调用valueForKey:方法读取对象属性或成员变量的值，和getter  setter方法不同的是，kvc可以读写私有属性和变量

kvo(Key Value Observe)用于观测对象属性的变化。kvo的底层机制是，创建一个类继承于要观测的对象的类，在类中添加要观测的属性，当要观测的属性值要改变时，重新调用创建的类中对应的setter方法，运用通知机制，发送通知给观察者。

kvo的运用：让UIScrollView的bounds始终等于contentSize

//

//  ViewController.m

//  NSOperation

//

//  Created by zmx on 16/1/8.

//  Copyright © 2016年 zmx. All rights reserved.

//

#import "ViewController.h"

#import "MyOperation.h"

@interface
ViewController ()

@property (nonatomic,
strong) NSOperationQueue *queue;

@end

@implementation ViewController

- (void)viewDidLoad {

    [super
viewDidLoad];

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

    MyOperation *op1 = [MyOperation
operationWithOpname:@"op1"];

    MyOperation *op2 = [MyOperation
operationWithOpname:@"op2"];

    [op1 setCompletionBlock:^{

        NSLog(@"op1 finish");

    }];

    [op2 setCompletionBlock:^{

        NSLog(@"op2 finish");

    }];

    self.queue = [[NSOperationQueue
alloc]
init];

    [self.queue
addOperation:op1];

    [self.queue
addOperation:op2];

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1
* NSEC_PER_SEC)),
dispatch_get_main_queue(), ^{

        [op2 cancel];

    });

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1
* NSEC_PER_SEC)),
dispatch_get_main_queue(), ^{

        [op1 cancel];

    });

}

@end