4.4 多线程进阶篇<下>（NSOperation）

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本文源码 Demo 详见 Github
https://github.com/shorfng/iOS-4.0-multithreading.git

1.0 NSOperation 的做用

使用 NSOperation 的目的就是为了让开发人员再也不关心线程

• 配合使用 NSOperation(任务) 和 NSOperationQueue(队列) 也能实现多线程编程

NSOperation 和 NSOperationQueue 实现多线程的具体步骤：

（1）先将须要执行的操做封装到一个NSOperation对象中

（2）而后将NSOperation对象添加到NSOperationQueue中

（3）系统会自动将NSOperationQueue中的NSOperation取出来

（4）将取出的NSOperation封装的操做放到一条新线程中执行

使用NSOperation子类的方式有3种：

NSOperation是个抽象类，并不具有封装操做的能力，必须使用它的子类

1. NSInvocationOperation

• NSBlockOperation
• 自定义子类继承NSOperation，实现内部相应的方法

2.0 NSInvocationOperation

//建立NSInvocationOperation对象
- (id)initWithTarget:(id)target selector:(SEL)sel object:(id)arg;

//调用start方法开始执行操做，一旦执行操做，就会调用target的sel方法
- (void)start;

注意：

• 默认状况下，操做对象在主线程中执行
• 调用了start方法后并不会开一条新线程去执行操做，只有添加到队列中才会开启新的线程
• 即默认状况下，若是操做没有放到队列中queue中，都是同步执行。
• 只有将NSOperation放到一个NSOperationQueue中，才会异步执行操做

---

代码示例：

#import "ViewController.h"

@interface ViewController ()
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

  //建立操做对象，封装要执行的任务
  NSInvocationOperation *op =
      [[NSInvocationOperation alloc] initWithTarget:self
                                           selector:@selector(run)
                                             object:nil];
  //执行操做
  [op start];
}

- (void)run {
  NSLog(@"------%@", [NSThread currentThread]);
}

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

打印结果：

NSInvocationOperation[862:29437] ------<NSThread: 0x7f9cea507920>{number = 1, name = main}

3.0 NSBlockOperation

//建立 NSBlockOperation 操做对象
+ (id)blockOperationWithBlock:(void (^)(void))block;

// 添加操做
- (void)addExecutionBlock:(void (^)(void))block;

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

---

代码示例：

#import "ViewController.h"

@interface ViewController ()
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

  // 1.建立 NSBlockOperation 操做对象
  NSBlockOperation *op = [NSBlockOperation blockOperationWithBlock:^{
    // 在主线程
    NSLog(@"下载1------%@", [NSThread currentThread]);
  }];

  // 2.添加操做（额外的任务）（在子线程执行)
  [op addExecutionBlock:^{
    NSLog(@"下载2------%@", [NSThread currentThread]);
  }];

  [op addExecutionBlock:^{
    
  [op addExecutionBlock:^{
    NSLog(@"下载2------%@", [NSThread currentThread]);
  }];
  [op addExecutionBlock:^{
    NSLog(@"下载3------%@", [NSThread currentThread]);
  }];
  [op addExecutionBlock:^{
    NSLog(@"下载4------%@", [NSThread currentThread]);
  }];
  // 3.开启执行操做
  [op start];
}
- (void)run {
  NSLog(@"------%@", [NSThread currentThread]);
}
- (void)didReceiveMemoryWarning {
  [super didReceiveMemoryWarning];
  // Dispose of any resources that can be recreated.
}
@end

打印结果：

NSBlockOperation[1013:37922] 下载1------<NSThread: 0x7feea1c05460>{number = 1, name = main}
NSBlockOperation[1013:37952] 下载2------<NSThread: 0x7feea1f0b790>{number = 2, name = (null)}
NSBlockOperation[1013:37955] 下载3------<NSThread: 0x7feea1c0f8a0>{number = 3, name = (null)}
NSBlockOperation[1013:37951] 下载4------<NSThread: 0x7feea1e0b520>{number = 4, name = (null)}

4.0 NSOperationQueue

NSOperationQueue的做用：添加操做到NSOperationQueue中，自动执行操做，自动开启线程

• NSOperation 能够调用 start 方法来执行任务，但默认是同步执行的
• 若是将 NSOperation 添加到 NSOperationQueue（操做队列）中，系统会自动异步执行NSOperation中的操做

添加操做到 NSOperationQueue 中：2种方式

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

- (void)addOperationWithBlock:(void (^)(void))block NS_AVAILABLE(10_6, 4_0);

---

代码示例：

#import "ViewController.h"

@interface ViewController ()
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  [self operationQueue2];
}

#pragma mark - 把操做添加到队列中,方式1：addOperation
- (void)operationQueue1 {
  // 1.建立队列
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  // 2.1 方式1：建立操做（任务）NSInvocationOperation ，封装操做
  NSInvocationOperation *op1 =
      [[NSInvocationOperation alloc] initWithTarget:self
                                           selector:@selector(download1)
                                             object:nil];

  // 2.2 方式2：建立NSBlockOperation ，封装操做
  NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"download2 --- %@", [NSThread currentThread]);
  }];

  // 添加操做
  [op2 addExecutionBlock:^{
    NSLog(@"download3 --- %@", [NSThread currentThread]);
  }];

  // 3.把操做（任务）添加到队列中，并自动调用 start 方法
  [queue addOperation:op1];
  [queue addOperation:op2];
}

- (void)download1 {
  NSLog(@"download1 --- %@", [NSThread currentThread]);
}

#pragma mark - 把操做添加到队列中,方式2：addOperationWithBlock
- (void)operationQueue2 {
  // 1.建立队列
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  // 2.添加操做到队列中
  [queue addOperationWithBlock:^{
    NSLog(@"download1 --- %@", [NSThread currentThread]);
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download2 --- %@", [NSThread currentThread]);
  }];
}

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

@end

打印结果：

NSOperationQueue[1658:89517] download2 --- <NSThread: 0x7f88a9e059d0>{number = 3, name = (null)}
 NSOperationQueue[1658:89518] download1 --- <NSThread: 0x7f88a9d901f0>{number = 2, name = (null)}
 NSOperationQueue[1658:89521] download3 --- <NSThread: 0x7f88a9d15d30>{number = 4, name = (null)}

 NSOperationQueue[1704:92509] download2 --- <NSThread: 0x7fd318f06540>{number = 2, name = (null)}
 NSOperationQueue[1704:92513] download1 --- <NSThread: 0x7fd318d0e460>{number = 3, name = (null)}

提示：队列的取出是有顺序的，与打印结果并不矛盾。这就比如，选手A,BC虽然起跑的顺序是先A,后B，而后C，可是到达终点的顺序却不必定是A,B在前，C在后。

4.1 最大并发数

并发数：同时执⾏行的任务数 好比,同时开3个线程执行3个任务,并发数就是3

最大并发数：同一时间最多只能执行的任务的个数

最⼤并发数的相关⽅方法：

//最大并发数，默认为-1
@property NSInteger maxConcurrentOperationCount;

- (void)setMaxConcurrentOperationCount:(NSInteger)cnt;

说明：

• 若是没有设置最大并发数，那么并发的个数是由系统内存和CPU决定的，内存多就开多一点，内存少就开少一点。
• 最⼤并发数的值并不表明线程的个数，仅仅表明线程的ID。
• 最大并发数不要乱写（5之内），不要开太多，通常以2~3为宜，由于虽然任务是在子线程进行处理的，可是cpu处理这些过多的子线程可能会影响UI，让UI变卡。
• 最大并发数的值为1，就变成了串行队列

---

代码示例：

#import "ViewController.h"

@interface ViewController ()
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  // 1.建立队列
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  // 2.设置最大并发操做数(大并发操做数 = 1,就变成了串行队列)
  queue.maxConcurrentOperationCount = 2;

  // 3.添加操做
  [queue addOperationWithBlock:^{
    NSLog(@"download1 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:0.01];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download2 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:0.01];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download3 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:0.01];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download4 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:0.01];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download5 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:0.01];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download6 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:0.01];
  }];
}

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

@end

打印结果：

最大并发数[1909:113433] download2 --- <NSThread: 0x7ffef240ba70>{number = 3, name = (null)}
最大并发数[1909:113432] download1 --- <NSThread: 0x7ffef24aee50>{number = 2, name = (null)}
最大并发数[1909:113432] download4 --- <NSThread: 0x7ffef24aee50>{number = 2, name = (null)}
最大并发数[1909:113431] download3 --- <NSThread: 0x7ffef251aa80>{number = 4, name = (null)}
最大并发数[1909:113428] download5 --- <NSThread: 0x7ffef2603d90>{number = 5, name = (null)}
最大并发数[1909:113432] download6 --- <NSThread: 0x7ffef24aee50>{number = 2, name = (null)}

4.2 队列的暂停和恢复

队列的暂停：当前任务结束后，暂停执行下一个任务，而非当前任务

//暂停和恢复队列（YES表明暂停队列，NO表明恢复队列）
- (void)setSuspended:(BOOL)b;

//当前状态
- (BOOL)isSuspended;

暂停和恢复的使用场合：

在tableview界面，开线程下载远程的网络界面，对UI会有影响，使用户体验变差。那么这种状况，就能够设置在用户操做UI（如滚动屏幕）的时候，暂停队列（不是取消队列），中止滚动的时候，恢复队列。

---

代码示例：

#import "ViewController.h"

@interface ViewController ()
@property(nonatomic, strong) NSOperationQueue *queue; //队列
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];

  // 1.建立队列
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  // 2.设置最大并发操做数(大并发操做数 = 1,就变成了串行队列)
  queue.maxConcurrentOperationCount = 1;

  // 3.添加操做
  [queue addOperationWithBlock:^{
    NSLog(@"download1 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:3];
  }];

  [queue addOperationWithBlock:^{
    NSLog(@"download2 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:3];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download3 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:3];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download4 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:3];
  }];

  self.queue = queue;
}

#pragma mark - 暂停和恢复
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  if (self.queue.isSuspended) {
    self.queue.suspended = NO; // 恢复队列，继续执行
  } else {
    self.queue.suspended = YES; // 暂停（挂起）队列，暂停执行
  }
}

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

@end

打印结果：

队列的暂停和恢复[2650:156206] download1 --- <NSThread: 0x7fd689f552b0>{number = 3, name = (null)}
队列的暂停和恢复[2650:156205] download2 --- <NSThread: 0x7fd689c02e70>{number = 2, name = (null)}
队列的暂停和恢复[2650:156206] download3 --- <NSThread: 0x7fd689f552b0>{number = 3, name = (null)}
队列的暂停和恢复[2650:156385] download4 --- <NSThread: 0x7fd689ea11c0>{number = 4, name = (null)}

4.3 队列的取消

取消队列的全部操做：相等于调用了全部 NSOperation 的 -(void)cancel 方法，
当前任务结束后，取消执行下面的全部任务，而非当前任务

// 也可调用NSOperation的 -(void)cancel 方法取消单个操做
- (void)cancelAllOperations;

---

代码示例：

#import "ViewController.h"

@interface ViewController ()
@property(nonatomic, strong) NSOperationQueue *queue; //队列
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];

  // 1.建立队列
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  // 2.设置最大并发操做数(大并发操做数 = 1,就变成了串行队列)
  queue.maxConcurrentOperationCount = 1;

  // 3.添加操做
  [queue addOperationWithBlock:^{
    NSLog(@"download1 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:3];
  }];

  [queue addOperationWithBlock:^{
    NSLog(@"download2 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:3];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download3 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:3];
  }];
  [queue addOperationWithBlock:^{
    NSLog(@"download4 --- %@", [NSThread currentThread]);
    [NSThread sleepForTimeInterval:3];
  }];

  self.queue = queue;
}

#pragma mark - 取消队列的全部操做
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  // 取消队列的全部操做（相等于调用了全部NSOperation的-(void)cancel方法）
  [self.queue cancelAllOperations];
}

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

@end

打印结果：

队列的取消[3041:167756] download1 --- <NSThread: 0x7fcc09543b40>{number = 3, name = (null)}
队列的取消[3041:167749] download2 --- <NSThread: 0x7fcc094505f0>{number = 2, name = (null)}

4.4 操做优先级

设置NSOperation在queue中的优先级，能够改变操做的执行优先级：

@property NSOperationQueuePriority queuePriority;

- (void)setQueuePriority:(NSOperationQueuePriority)p;

优先级的取值：优先级高的任务，调用的概率会更大

typedef NS_ENUM(NSInteger, NSOperationQueuePriority) {
NSOperationQueuePriorityVeryLow = -8L,
NSOperationQueuePriorityLow = -4L,
NSOperationQueuePriorityNormal = 0,
NSOperationQueuePriorityHigh = 4,
NSOperationQueuePriorityVeryHigh = 8
};

4.5 操做依赖

NSOperation之间能够设置依赖来保证执行顺序：不能循环依赖（不能A依赖于B，B又依赖于A）

// 操做B依赖于操做A（必定要让操做A执行完后，才能执行操做B）
[operationB addDependency:operationA];

能够在不一样queue的NSOperation之间建立依赖关系（跨队列依赖）：

注意：

• 必定要在把操做添加到队列以前，进行设置操做依赖。
• 任务添加的顺序并不可以决定执行顺序，执行的顺序取决于依赖。

---

代码示例：

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  //建立对象，封装操做
  NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"download1----%@", [NSThread currentThread]);
  }];
  NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"download2----%@", [NSThread currentThread]);
  }];
  NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"download3----%@", [NSThread currentThread]);
  }];
  NSBlockOperation *op4 = [NSBlockOperation blockOperationWithBlock:^{
    for (NSInteger i = 0; i < 5; i++) {
      NSLog(@"download4----%@", [NSThread currentThread]);
    }
  }];

  NSBlockOperation *op5 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"download5----%@", [NSThread currentThread]);
  }];
  //操做的监听
  op5.completionBlock = ^{
    NSLog(@"op5执行完毕---%@", [NSThread currentThread]);
  };

  //设置操做依赖（op4执行完，才执行 op3）
  [op3 addDependency:op1];
  [op3 addDependency:op2];
  [op3 addDependency:op4];

  //把操做添加到队列中
  [queue addOperation:op1];
  [queue addOperation:op2];
  [queue addOperation:op3];
  [queue addOperation:op4];
  [queue addOperation:op5];
}

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

@end

打印结果：

操做依赖[4196:150518] download5----<NSThread: 0x7ffa61d177d0>{number = 3, name = (null)}
操做依赖[4196:150506] download1----<NSThread: 0x7ffa61ca6b90>{number = 4, name = (null)}
操做依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操做依赖[4196:150510] download2----<NSThread: 0x7ffa61f0e800>{number = 5, name = (null)}
操做依赖[4196:150518] op5执行完毕---<NSThread: 0x7ffa61d177d0>{number = 3, name = (null)}
操做依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操做依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操做依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操做依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操做依赖[4196:150509] download3----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}

操做的监听

能够监听一个操做的执行完毕：

@property (nullable, copy) void (^completionBlock)(void);

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

代码详见4.5 操做依赖 示例代码

5.0 线程间通讯（图片下载示例）

#import "ViewController.h"

@interface ViewController ()
@property(weak, nonatomic) IBOutlet UIImageView *imageView;

@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  [self test2];
}

#pragma mark - 线程间通讯（图片合成）
- (void)test1 {
  // 1.队列
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  __block UIImage *image1 = nil;
  // 2.下载图片1
  NSBlockOperation *download1 = [NSBlockOperation blockOperationWithBlock:^{
    // 图片的网络路径
    NSURL *url =
        [NSURL URLWithString:@"http://img.pconline.com.cn/images/photoblog/9/9/"
                             @"8/1/9981681/200910/11/1255259355826.jpg"];
    // 加载图片
    NSData *data = [NSData dataWithContentsOfURL:url];
    // 生成图片
    image1 = [UIImage imageWithData:data];
  }];

  __block UIImage *image2 = nil;
  // 3.下载图片2
  NSBlockOperation *download2 = [NSBlockOperation blockOperationWithBlock:^{
    // 图片的网络路径
    NSURL *url = [NSURL
        URLWithString:
            @"http://pic38.nipic.com/20140228/5571398_215900721128_2.jpg"];
    // 加载图片
    NSData *data = [NSData dataWithContentsOfURL:url];
    // 生成图片
    image2 = [UIImage imageWithData:data];
  }];

  // 4.合成图片
  NSBlockOperation *combine = [NSBlockOperation blockOperationWithBlock:^{
    // 开启新的图形上下文
    UIGraphicsBeginImageContext(CGSizeMake(100, 100));

    // 绘制图片1
    [image1 drawInRect:CGRectMake(0, 0, 50, 100)];
    image1 = nil;

    // 绘制图片2
    [image2 drawInRect:CGRectMake(50, 0, 50, 100)];
    image2 = nil;

    // 取得上下文中的图片
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

    // 结束上下文
    UIGraphicsEndImageContext();

    // 5.回到主线程
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
      self.imageView.image = image;
    }];
  }];

  // 设置依赖操做
  [combine addDependency:download1];
  [combine addDependency:download2];

  //把操做添加到队列中
  [queue addOperation:download1];
  [queue addOperation:download2];
  [queue addOperation:combine];
}

#pragma mark - 线程间通讯（图片下载）
- (void)test2 {
  [[[NSOperationQueue alloc] init] addOperationWithBlock:^{
    // 图片的网络路径
    NSURL *url =
        [NSURL URLWithString:@"http://img.pconline.com.cn/images/photoblog/9/9/"
                             @"8/1/9981681/200910/11/1255259355826.jpg"];

    // 加载图片
    NSData *data = [NSData dataWithContentsOfURL:url];

    // 生成图片
    UIImage *image = [UIImage imageWithData:data];

    // 回到主线程
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
      self.imageView.image = image;
    }];
  }];
}

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

@end

6.0 自定义NSOperation

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

重写- (void)main方法的注意点：

• 本身建立自动释放池（由于若是是异步操做，没法访问主线程的自动释放池）
• 常常经过- (BOOL)isCancelled方法检测操做是否被取消，对取消作出响应

---

ViewController.m

#import "TDOperation.h"
#import "ViewController.h"

@interface ViewController ()
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

  // 1.建立队列
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  // 2.建立自定义 TDGOperation
  TDOperation *op = [[TDOperation alloc] init];

  // 3.把操做（任务）添加到队列中，并自动调用 start 方法
  [queue addOperation:op];
}

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

TDOperation.h(继承自：NSOperation)

#import <Foundation/Foundation.h>

@interface TDOperation : NSOperation
@end

TDOperation.m

#import "TDOperation.h"

@implementation TDOperation
//须要执行的任务
- (void)main {
  for (NSInteger i = 0; i < 3; i++) {
    NSLog(@"download1 -%zd-- %@", i, [NSThread currentThread]);
  }
  // 人为的判断是否执行取消操做，若是执行取消操做，就直接 return 不往下执行
  if (self.isCancelled)
    return;

  for (NSInteger i = 0; i < 3; i++) {
    NSLog(@"download2 -%zd-- %@", i, [NSThread currentThread]);
  }
  // 人为的判断是否执行取消操做，若是执行取消操做，就直接 return 不往下执行
  if (self.isCancelled)
    return;

  for (NSInteger i = 0; i < 3; i++) {
    NSLog(@"download3 -%zd-- %@", i, [NSThread currentThread]);
  }
  // 人为的判断是否执行取消操做，若是执行取消操做，就直接 return 不往下执行
  if (self.isCancelled)
    return;
}
@end

运行结果：

自定义NSOperation[1567:84075] download1 -0-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download1 -1-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download1 -2-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download2 -0-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download2 -1-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download2 -2-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download3 -0-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download3 -1-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download3 -2-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}

6.1 自定义NSOperation队列的取消操做

代码示例：

ViewController.m

#import "TDOperation.h"
#import "ViewController.h"

@interface ViewController ()
@property(nonatomic, strong) NSOperationQueue *queue; //队列
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];

  // 1.建立队列
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];

  // 2.设置最大并发操做数(大并发操做数 = 1,就变成了串行队列)
  queue.maxConcurrentOperationCount = 2;

  // 3.添加操做 - 自定义 NSOperation
  [queue addOperation:[[TDOperation alloc] init]];

  self.queue = queue;
}

#pragma mark - 取消队列的全部操做
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  // 取消队列的全部操做（相等于调用了全部NSOperation的-(void)cancel方法）
  [self.queue cancelAllOperations];
}

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

@end

TDOperation.h

#import <Foundation/Foundation.h>

@interface TDOperation : NSOperation

@end

TDOperation.m

#import "TDOperation.h"

@implementation TDOperation
//须要执行的任务
- (void)main {
  for (NSInteger i = 0; i < 1000; i++) {
    NSLog(@"download1 -%zd-- %@", i, [NSThread currentThread]);
  }
  // 人为的判断是否执行取消操做，若是执行取消操做，就直接 return 不往下执行
  if (self.isCancelled)
    return;

  for (NSInteger i = 0; i < 1000; i++) {
    NSLog(@"download2 -%zd-- %@", i, [NSThread currentThread]);
  }
  // 人为的判断是否执行取消操做，若是执行取消操做，就直接 return 不往下执行
  if (self.isCancelled)
    return;

  for (NSInteger i = 0; i < 1000; i++) {
    NSLog(@"download3 -%zd-- %@", i, [NSThread currentThread]);
  }
  // 人为的判断是否执行取消操做，若是执行取消操做，就直接 return 不往下执行
  if (self.isCancelled)
    return;
}
@end

6.2 多图下载

沙盒结构：

Documents
 Library
    - Caches
    - Preference
 tmp

自定义NSOperation下载图片思路 – 有沙盒缓存

---

代码示例：

ViewController.m

#import "TDApp.h"
#import "ViewController.h"

@interface ViewController ()
@property(nonatomic, strong) NSArray *apps;                   //全部数据
@property(nonatomic, strong) NSMutableDictionary *imageCache; //内存缓存的图片
@property(nonatomic, strong) NSOperationQueue *queue;         //队列对象
@property(nonatomic, strong) NSMutableDictionary *operations; //全部的操做对象

@end

@implementation ViewController

- (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;
}

#pragma mark - Cell
- (UITableViewCell *)tableView:(UITableView *)tableView
         cellForRowAtIndexPath:(NSIndexPath *)indexPath {

  // 重用标识
  static NSString *ID = @"app";
  UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];

  TDApp *app = self.apps[indexPath.row];

#pragma mark - app 名称
  cell.textLabel.text = app.name;

#pragma mark - 下载量
  cell.detailTextLabel.text = app.download;

#pragma mark - 图片
  // 1.先从内存缓存中取出图片
  UIImage *image = self.imageCache[app.icon];

  // 2.判断内存中是否有图片
  if (image) {
    // 2.1 内存中有图片，直接设置图片
    cell.imageView.image = image;
  } else {
    // 2.2 内存中没有图片，将图片文件数据写入沙盒中

    //（1）得到Library/Caches文件夹
    NSString *cachesPath = [NSSearchPathForDirectoriesInDomains(
        NSCachesDirectory, NSUserDomainMask, YES) firstObject];
    //（2）得到文件名
    NSString *filename = [app.icon lastPathComponent];
    //（3）计算出文件的全路径
    NSString *file = [cachesPath stringByAppendingPathComponent:filename];
    //（4）加载沙盒的文件数据
    NSData *data = [NSData dataWithContentsOfFile:file];

    // 2.3 判断沙盒中是否有图片
    if (data) {

      // 有图片，直接利用沙盒中图片，设置图片
      UIImage *image = [UIImage imageWithData:data];
      cell.imageView.image = image;
      // 并将图片存到字典中
      self.imageCache[app.icon] = image;

    } else {

      // 没有图片,先设置一个占位图
      cell.imageView.image = [UIImage imageNamed:@"placeholder"];

      // 取出图片，并判断这张图片是否有下载操做
      NSOperation *operation = self.operations[app.icon];
      if (operation == nil) {
        // 若是这张图片暂时没有下载操做，则须要建立一个下载操做
        // 下载图片是耗时操做，放到子线程
        operation = [NSBlockOperation blockOperationWithBlock:^{
          // 下载图片
          NSData *data =
              [NSData dataWithContentsOfURL:[NSURL URLWithString:app.icon]];
          // 若是数据下载失败
          if (data == nil) {
            // 下载失败，移除操做
            [self.operations removeObjectForKey:app.icon];
            return;
          }

            // 下载成功，将图片放在 image 中
          UIImage *image = [UIImage imageWithData:data];
          // 存到字典中
          self.imageCache[app.icon] = image;

          //回到主线程显示图片
          [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            [tableView reloadRowsAtIndexPaths:@[ indexPath ]
                             withRowAnimation:UITableViewRowAnimationNone];
          }];

          // 将图片文件数据写入沙盒中
          [data writeToFile:file atomically:YES];
          // 下载完毕，移除操做
          [self.operations removeObjectForKey:app.icon];
        }];

        // 添加到队列中（队列的操做不须要移除，会自动移除）
        [self.queue addOperation:operation];
        // 并将图片存到字典中
        self.operations[app.icon] = operation;
      }
    }
  }

  return cell;
}

#pragma mark - 数据懒加载
- (NSArray *)apps {
  if (!_apps) {
    NSArray *dictArray =
        [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle]
                                             pathForResource:@"apps.plist"
                                                      ofType:nil]];

    NSMutableArray *appArray = [NSMutableArray array];
    for (NSDictionary *dict in dictArray) {
      [appArray addObject:[TDApp appWithDict:dict]];
    }
    _apps = appArray;
  }
  return _apps;
}

#pragma mark - 懒加载
- (NSMutableDictionary *)imageCache {
  if (!_imageCache) {
    _imageCache = [NSMutableDictionary dictionary];
  }
  return _imageCache;
}

#pragma mark - 懒加载
- (NSOperationQueue *)queue {
  if (!_queue) {
    _queue = [[NSOperationQueue alloc] init];
    _queue.maxConcurrentOperationCount = 3;
  }
  return _queue;
}

#pragma mark - 懒加载
- (NSMutableDictionary *)operations {
  if (!_operations) {
    _operations = [NSMutableDictionary dictionary];
  }
  return _operations;
}

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

@end

TDApp.h

#import <Foundation/Foundation.h>

@interface TDApp : NSObject

@property(nonatomic, strong) NSString *icon;     // 图片
@property(nonatomic, strong) NSString *download; //下载量
@property(nonatomic, strong) NSString *name;     // 名字

+ (instancetype)appWithDict:(NSDictionary *)dict;

@end

TDApp.m

#import "TDApp.h"

@implementation TDApp

+ (instancetype)appWithDict:(NSDictionary *)dict {
  TDApp *app = [[self alloc] init];
  [app setValuesForKeysWithDictionary:dict];
  return app;
}

@end

6.3 多图下载 - SDWebImage

SDWebImage：

• iOS中著名的网络图片处理框架
• 包含的功能：图片下载、图片缓存、下载进度监听、gif处理等等

• 框架地址：https://github.com/rs/SDWebImage

• SDWebImage的图片缓存周期是:1周

---

代码示例：

ViewController.m

#import "TDApp.h"
#import "UIImageView+WebCache.h"
#import "ViewController.h"

@interface ViewController ()
@property(nonatomic, strong) NSArray *apps;                   //全部数据
@property(nonatomic, strong) NSMutableDictionary *imageCache; //内存缓存的图片
@property(nonatomic, strong) NSOperationQueue *queue;         //队列对象
@property(nonatomic, strong) NSMutableDictionary *operations; //全部的操做对象

@end

@implementation ViewController

- (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;
}

#pragma mark - Cell
- (UITableViewCell *)tableView:(UITableView *)tableView
         cellForRowAtIndexPath:(NSIndexPath *)indexPath {

  // 重用标识
  static NSString *ID = @"app";
  UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];

  TDApp *app = self.apps[indexPath.row];

#pragma mark - app 名称
  cell.textLabel.text = app.name;

#pragma mark - 下载量
  cell.detailTextLabel.text = app.download;

#pragma mark - 图片
  // expectedSize: 图片的总字节数  receivedSize: 已经接收的图片字节数
  [cell.imageView sd_setImageWithURL:[NSURL URLWithString:app.icon]
      placeholderImage:[UIImage imageNamed:@"placeholder"]
      options:0 // 0 表示什么都不作
      progress:^(NSInteger receivedSize, NSInteger expectedSize) {

        NSLog(@"下载进度：%f", 1.0 * receivedSize / expectedSize);
      }
      completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType,
                  NSURL *imageURL) {
        NSLog(@"下载完图片");
      }];
  return cell;
}

#pragma mark - 数据懒加载
- (NSArray *)apps {
  if (!_apps) {
    NSArray *dictArray =
        [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle]
                                             pathForResource:@"apps.plist"
                                                      ofType:nil]];

    NSMutableArray *appArray = [NSMutableArray array];
    for (NSDictionary *dict in dictArray) {
      [appArray addObject:[TDApp appWithDict:dict]];
    }
    _apps = appArray;
  }
  return _apps;
}

#pragma mark - 懒加载
- (NSMutableDictionary *)imageCache {
  if (!_imageCache) {
    _imageCache = [NSMutableDictionary dictionary];
  }
  return _imageCache;
}

#pragma mark - 懒加载
- (NSOperationQueue *)queue {
  if (!_queue) {
    _queue = [[NSOperationQueue alloc] init];
    _queue.maxConcurrentOperationCount = 3;
  }
  return _queue;
}

#pragma mark - 懒加载
- (NSMutableDictionary *)operations {
  if (!_operations) {
    _operations = [NSMutableDictionary dictionary];
  }
  return _operations;
}

#pragma mark - 设置控制器的内存警告
- (void)didReceiveMemoryWarning {
  [super didReceiveMemoryWarning];

  self.imageCache = nil;
  self.operations = nil;
  [self.queue cancelAllOperations];
}

@end

TDApp.h

#import <Foundation/Foundation.h>

@interface TDApp : NSObject

@property(nonatomic, strong) NSString *icon;     // 图片
@property(nonatomic, strong) NSString *download; //下载量
@property(nonatomic, strong) NSString *name;     // 名字

+ (instancetype)appWithDict:(NSDictionary *)dict;

@end

TDApp.m

#import "TDApp.h"

@implementation TDApp

+ (instancetype)appWithDict:(NSDictionary *)dict {
  TDApp *app = [[self alloc] init];
  [app setValuesForKeysWithDictionary:dict];
  return app;
}

@end

7.0【区别】GCD & NSOperationQueue 队列类型的建立方式

GCD 队列类型的建立方式：

（1）并发队列：手动建立、全局

（2）串行队列：手动建立、主队列

---

NSOperationQueue的队列类型的建立方法：

（1）主队列：[NSOperationQueue mainQueue]

• 凡是添加到主队列中的任务（NSOperation），都会放到主线程中执行

（2）其余队列（同时包含了串行、并发功能）：[NSOperationQueue alloc]init]

• 添加到这种队列中的任务（NSOperation），就会自动放到子线程中执行

---

注：关于SDWebImage框架的详解会另外再写博客

若是你以为本篇文章对你有所帮助，请点击文章末尾右下角“推荐”，^_^

做者：蓝田（Loto）

出处：http://www.cnblogs.com/shorfng/

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