NSOperation

 
http://www.cnblogs.com/dyf520/p/3805297.html
 
 
-------NSOperation简介----
1.NSOperation的作用
·配合使用NSOperation和NSOperationQueue也能实现多线程编程
 
2.NSOperation和NSOperationQueue实现多线程的具体步骤
·先将需要执行的操作封装到一个NSOperation对象中
·然后将NSOperation对象添加到NSOperationQueue中
·系统会自动将NSOperation中封装的操作放到一条新线程中执行
 
---------NSOperation的子类----
3.NSOperation是个抽象类，并不具备封装操作的能力，必须使用它的子类
 
4.使用NSOperation子类的方式有3种
·NSInvocationOperation
·NSBlockOperation
·自定义子类继承NSOperation，实现内部相应的方法
 
------NSInvocationOperation---
5.创建NSInvocationOperation对象

- (id)initWithTarget:(id)target selector:(SEL)sel object:(id)arg;

6.调用start方法开始执行操作

- (void)start;

一旦执行操作，就会调用target的sel方法

7.注意
·默认情况下，调用了start方法后并不会开一条新线程去执行操作，而是在当前线程同步执行操作
·只有将NSOperation放到一个NSOperationQueue中，才会异步执行操作
 
 
-------NSBlockOperation--
8.创建NSBlockOperation对象

+ (id)blockOperationWithBlock:(void (^)(void))block;

9.通过addExecutionBlock:方法添加更多的操作

- (void)addExecutionBlock:(void (^)(void))block;

注意：只要NSBlockOperation封装的操作数 > 1，就会异步执行操作

-------NSOperationQueue----

10.NSOperationQueue的作用
·NSOperation可以调用start方法来执行任务，但默认是同步执行的
·如果将NSOperation添加到NSOperationQueue（操作队列）中，系统会自动异步执行NSOperation中的操作
 
11.添加操作到NSOperationQueue中

- (void)addOperation:(NSOperation *)op;

- (void)addOperationWithBlock:(void (^)(void))block;

-------最大并发数----

12.什么是并发数
·同时执行的任务数
·比如，同时开3个线程执行3个任务，并发数就是3
 
13.最大并发数的相关方法

- (NSInteger)maxConcurrentOperationCount;

- (void)setMaxConcurrentOperationCount:(NSInteger)cnt;

-----队列的取消、暂停、恢复------

14.取消队列的所有操作

- (void)cancelAllOperations;

提示：也可以调用NSOperation的- (void)cancel方法取消单个操作

15.暂停和恢复队列

- (void)setSuspended:(BOOL)b; // YES代表暂停队列，NO代表恢复队列

- (BOOL)isSuspended;

----操作优先级-----

16.设置NSOperation在queue中的优先级，可以改变操作的执行顺序

- (NSOperationQueuePriority)queuePriority;

- (void)setQueuePriority:(NSOperationQueuePriority)p;

17.优先级的取值（优先级越高，越先执行）
·NSOperationQueuePriorityVeryLow = -8L,
·NSOperationQueuePriorityLow = -4L,
·NSOperationQueuePriorityNormal = 0,
·NSOperationQueuePriorityHigh = 4,
·NSOperationQueuePriorityVeryHigh = 8
 
---操作依赖---
18.NSOperation之间可以设置依赖来保证执行顺序
·比如一定要让操作A执行完后，才能执行操作B，可以这么写

[operationB addDependency:operationA]; // 操作B依赖于操作A

19.可以在不同queue的NSOperation之间创建依赖关系

20.注意：不能相互依赖

·比如A依赖B，B依赖A
----操作的执行顺序---
21.对于添加到queue中的operations，它们的执行顺序取决于2点
·首先依据NSOperation之间的依赖关系
·然后依据NSOperation的优先级
 
22.因此，总体的执行顺序是
·先满足依赖关系
·然后再从NSOperation中选择优先级最高的那个执行
 
 
 
---自定义NSOperation---
23.自定义NSOperation的步骤很简单
·重写- (void)main方法，在里面实现想执行的任务
 
24.重写- (void)main方法的注意点
·自己创建自动释放池（因为如果是异步操作，无法访问主线程的自动释放池）
·经常通过- (BOOL)isCancelled方法检测操作是否被取消，对取消做出响应
 
 
 
--------分割线---
NSOperation小代码1，
只写一个文件参考下
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//  DYFViewController.m
//  624-03-NSOperation
//
//  Created by dyf on 14-6-24.
//  Copyright (c) 2014年 ___FULLUSERNAME___. All rights reserved.
//
 
#import "DYFViewController.h"
 
@interface DYFViewController ()
 
@end
 
@implementation DYFViewController
 
- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
     
   
    [self testOperationQueue];
}
 
- (void)testOperationListen {
    NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"下载图片1111111%@", [NSThread currentThread]);
        // 下载图片
    }];
    operation3.completionBlock = ^{
        // 下载完图片后想做的时期
    };
    // 2.创建队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
 
    [queue addOperation:operation3];
 
}
 
- (void)testOperationQueue {
    // 1.封装操作
    NSInvocationOperation *operation1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(download) object:nil];
    NSInvocationOperation *operation2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(run) object:nil];
     
    NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"1111111%@", [NSThread currentThread]);
    }];
     
    [operation3 addExecutionBlock:^{
        NSLog(@"222222%@", [NSThread currentThread]);
    }];
    [operation3 addExecutionBlock:^{
        NSLog(@"33333%@", [NSThread currentThread]);
    }];
    // 2.创建队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    // 5以内，2~3为宜
    queue.maxConcurrentOperationCount = 2;
#warning 面试题
    // 设置操作依赖(一定要在添加到队列中前设置)
    [operation2 addDependency:operation1]; // 执行顺序取决于依赖，先执行完operation1再执行operation2
// 注意：不能相互依赖，循环操作
     
    // 3.添加操作到队列中（自动执行操作，自动开启线程）
    [queue addOperation:operation1];
    [queue addOperation:operation2];
    [queue addOperation:operation3];
     
    // 取消所有线程
    //[queue cancelAllOperations];
     
    // 暂停队列
    //[queue setSuspended:YES];
     
    // 设置操作优先级
    //operation1.queuePriority = NSOperationQueuePriorityVeryHigh;
     
     
}
 
- (void)testNSBlockOperation {
    // 1.创建操作对象，封装要执行的任务
    NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
        for (int i = 0; i < 11; i++) {
            NSLog(@"1111111%@", [NSThread currentThread]);
        }
    }];
    // 任务数在2各以上，就会开线程
    [operation addExecutionBlock:^{
        for (int i = 0; i < 11; i++) {
            NSLog(@"222222%@", [NSThread currentThread]);
        }
    }];
    [operation addExecutionBlock:^{
        for (int i = 0; i < 11; i++) {
            NSLog(@"33333%@", [NSThread currentThread]);
        }
    }];
 
    // 2.执行操作
    [operation start];
}
 
- (void)testNSInvocationOperation {
    // 1.创建操作对象，封装要执行的任务
    NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(download) object:nil];
    // 2.执行操作(默认情况下，若操作没有放到队列queue中，都是同步执行)
    [operation start];
}
 
- (void)download
{
    for (int i = 0; i < 11; i++) {
        NSLog(@"download-----%@", [NSThread currentThread]);
    }
}
 
- (void)run
{
    for (int i = 0; i < 11; i++) {
        NSLog(@"run------%@", [NSThread currentThread]);
    }
}
 
@end

----自定义NSOperation---

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//
//  DYFDownloadOperation.h
//  624-05-自定义Operation
//
//  Created by dyf on 14-6-24.
//  Copyright (c) 2014年 dyf. All rights reserved.
//
 
#import <Foundation/Foundation.h>
 
@class DYFDownloadOperation;
@protocol DYFDownloadOperationDelegate <NSObject>
 
@optional
- (void)downloadOperation:(DYFDownloadOperation *)operation didFinishedDownload:(UIImage *)image;
 
@end
 
@interface DYFDownloadOperation : NSOperation
 
@property (nonatomic, copy) NSString *url;
@property (nonatomic, strong) NSIndexPath *indexPath;
 
@property (nonatomic, weak) id<DYFDownloadOperationDelegate> delegate;
 
@end
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//
//  DYFDownloadOperation.m
//  624-05-自定义Operation
//
//  Created by dyf on 14-6-24.
//  Copyright (c) 2014年 dyf. All rights reserved.
//
 
#import "DYFDownloadOperation.h"
 
@implementation DYFDownloadOperation
/**
 *  在main方法中实现具体操作
 */
- (void)main
{
    @autoreleasepool {
        if (self.isCancelled) return;
        NSURL *imaUrl = [NSURL URLWithString:self.url];
        if (self.isCancelled) return;
        // 下面这行很耗时
        NSData *data = [NSData dataWithContentsOfURL:imaUrl];
        if (self.isCancelled) return;
        UIImage *image = [UIImage imageWithData:data];
        if (self.isCancelled) return;
         
        // 返回主线程显示图片
        // 通过代理
        if ([self.delegate respondsToSelector:@selector(downloadOperation:didFinishedDownload:)]) {
            [self.delegate downloadOperation:self didFinishedDownload:image];
        }
    }
}
 
@end

具体利用MVC模式创建的文件老生常谈，只来一个Controller.m文件供参考，数据存储存在问题，可以改用SDWebImage框架处理

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//
//  DYFTableViewController.m
//  624-05-自定义Operation
//
//  Created by dyf on 14-6-24.
//  Copyright (c) 2014年 ___FULLUSERNAME___. All rights reserved.
//
 
#import "DYFTableViewController.h"
#import "DYFAppModel.h"
#import "DYFDownloadOperation.h"
 
#warning Dictionary基础知识不太理解，字典的赋值回去看看笔记
@interface DYFTableViewController ()<DYFDownloadOperationDelegate>
 
@property (nonatomic, strong) NSArray *apps;
@property (nonatomic, strong) NSOperationQueue *queue;
 
/**
 *  key:url   value:operation对象
 */
@property (nonatomic, strong) NSMutableDictionary *oprations;
/**
 *  key:url   value:image对象
 */
@property (nonatomic, strong) NSMutableDictionary *images;
 
@end
 
@implementation DYFTableViewController
 
#pragma mark - 4个懒加载
- (NSArray *)apps
{
    if (!_apps) {
        NSString *path = [[NSBundle mainBundle] pathForResource:@"apps" ofType:@"plist"];
        NSArray *arrayApps = [NSArray arrayWithContentsOfFile:path];
         
        NSMutableArray *arrayM = [NSMutableArray arrayWithCapacity:arrayApps.count];
        for (NSDictionary *dict in arrayApps) {
            DYFAppModel *appM = [DYFAppModel appWithDict:dict];
            [arrayM addObject:appM];
        }
        _apps = arrayM;
    }
    return _apps;
}
- (NSOperationQueue *)queue
{
    if (!_queue) {
        _queue = [[NSOperationQueue alloc] init];
        // 设置最大并发线程数，最多同时下载3张图片
        _queue.maxConcurrentOperationCount = 3;
    }
    return _queue;
}
- (NSMutableDictionary *)oprations
{
    if (!_oprations) {
        _oprations = [[NSMutableDictionary alloc] init];
    }
    return _oprations;
}
- (NSMutableDictionary *)images
{
    if (!_images) {
        _images = [NSMutableDictionary dictionary];
    }
    return _images;
}
 
- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}
 
#pragma mark - 数据源方法
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return self.apps.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // 1.创建cell
    static NSString *identifier = @"apps";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:identifier];
    }
    // 2.设置cell的数据
    DYFAppModel *app = self.apps[indexPath.row];
    cell.textLabel.text = app.name;
    cell.detailTextLabel.text = app.download;
     
    // 重点是如何从网络下载图片传入cell上面
    // 每个url对应一个DYFDownloadOperation对象
    // 每个url对应一个image对象
    UIImage *image = self.images[app.icon];
    if (image) {
        // 若缓存中存在图片
        cell.imageView.image = image;
    }else
    {
        // 若缓存中不存在图片，则图片要从网上下载
        // 设置下载前系统刷出的图片
        cell.imageView.image = [UIImage imageNamed:@"身份证小"];
         
        // 基础差，下面这行不太理解
        DYFDownloadOperation *operation = self.oprations[app.icon];
        if (operation) {
            // 若正在下载，则不执行其它操作
        }else
        {
            // 若没在下载，则创建开始下载的子线程
            DYFDownloadOperation *operation = [[DYFDownloadOperation alloc] init];
            operation.url = app.icon;
            operation.indexPath = indexPath;
            operation.delegate = self;
            // 添加任务进队列，异步下载
            [self.queue addOperation:operation];
            // 基础差，下面这行不太理解
            self.oprations[app.icon] = operation;
        }
    }
     
    // 3.返回cell
    return cell;
}
 
#pragma mark - DYFDownloadOperationDelegate
- (void)downloadOperation:(DYFDownloadOperation *)operation didFinishedDownload:(UIImage *)image
{
    // 1.删除执行完毕的下载操作
    [self.oprations removeObjectForKey:operation.url];
    // 若图片下载好
    if (image) {
        // 2.将下载好的图片存入缓存
        self.images[operation.url] = image;
        // 3.刷新这一行cell的数据
        [self.tableView reloadRowsAtIndexPaths:@[operation.indexPath] withRowAnimation:UITableViewRowAnimationNone];
        // 4.将图片存入沙盒
         
        // 4.1图片先转换为2进制数据
        NSData *data = UIImagePNGRepresentation(image);
        // 4.2设置沙盒路径
        NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:[self.apps[operation.indexPath.row] icon]];
        NSLog(@"%@", path);
        // 4.3保存data到path中
        [data writeToFile:path atomically:YES];
    }
}
 
// 开始拖拽时候暂停队列
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
    [self.queue setSuspended:YES];
}
// 停止拖拽的时候重启队列
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{
    [self.queue setSuspended:NO];
}
 
@end
 
 
 
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原文地址：https://www.cnblogs.com/Cheetah-yang/p/4664010.html