4.4 多线程进阶篇<下>（NSOperation）

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发布时间：2019-06-13

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本文源码 Demo 详见 Github

https://github.com/shorfng/iOS-4.0-multithreading.git

1.0 NSOperation 的作用

使用 NSOperation 的目的就是为了让开发人员不再关心线程

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）先将需要执行的操作封装到一个NSOperation对象中

（2）然后将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封装的操作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，并不具备封装操作的能力，必须使用它的子类

NSInvocationOperation

NSBlockOperation

自定义子类继承NSOperation，实现内部相应的方法

2.0 NSInvocationOperation

//创建NSInvocationOperation对象- (id)initWithTarget:(id)target selector:(SEL)sel object:(id)arg;//调用start方法开始执行操作，一旦执行操作，就会调用target的sel方法- (void)start;

注意：

默认情况下，操作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作，只有添加到队列中才会开启新的线程

即默认情况下，如果操作没有放到队列中queue中，都是同步执行。

只有将NSOperation放到一个NSOperationQueue中，才会异步执行操作

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 {  //创建操作对象，封装要执行的任务  NSInvocationOperation *op =      [[NSInvocationOperation alloc] initWithTarget:self                                           selector:@selector(run)                                             object:nil];  //执行操作  [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] ------
    
     {number = 1, name = main}

3.0 NSBlockOperation

//创建 NSBlockOperation 操作对象+ (id)blockOperationWithBlock:(void (^)(void))block;// 添加操作- (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

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.创建 NSBlockOperation 操作对象  NSBlockOperation *op = [NSBlockOperation blockOperationWithBlock:^{    // 在主线程    NSLog(@"下载1------%@", [NSThread currentThread]);  }];  // 2.添加操作（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.开启执行操作  [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------
    
     {number = 1, name = main}NSBlockOperation[1013:37952] 下载2------
     
      {number = 2, name = (null)}NSBlockOperation[1013:37955] 下载3------
      
       {number = 3, name = (null)}NSBlockOperation[1013:37951] 下载4------
       
        {number = 4, name = (null)}

4.0 NSOperationQueue

NSOperationQueue的作用：添加操作到NSOperationQueue中，自动执行操作，自动开启线程

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

添加操作到 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 - 把操作添加到队列中,方式1：addOperation- (void)operationQueue1 {  // 1.创建队列  NSOperationQueue *queue = [[NSOperationQueue alloc] init];  // 2.1 方式1：创建操作（任务）NSInvocationOperation ，封装操作  NSInvocationOperation *op1 =      [[NSInvocationOperation alloc] initWithTarget:self                                           selector:@selector(download1)                                             object:nil];  // 2.2 方式2：创建NSBlockOperation ，封装操作  NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"download2 --- %@", [NSThread currentThread]);  }];  // 添加操作  [op2 addExecutionBlock:^{    NSLog(@"download3 --- %@", [NSThread currentThread]);  }];  // 3.把操作（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 - 把操作添加到队列中,方式2：addOperationWithBlock- (void)operationQueue2 {  // 1.创建队列  NSOperationQueue *queue = [[NSOperationQueue alloc] init];  // 2.添加操作到队列中  [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 --- 
    
     {number = 3, name = (null)} NSOperationQueue[1658:89518] download1 --- 
     
      {number = 2, name = (null)} NSOperationQueue[1658:89521] download3 --- 
      
       {number = 4, name = (null)} NSOperationQueue[1704:92509] download2 --- 
       
        {number = 2, name = (null)} NSOperationQueue[1704:92513] download1 --- 
        
         {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。这就好比，选手A,BC虽然起跑的顺序是先A,后B，然后C，但是到达终点的顺序却不一定是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比如,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：

如果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代表线程的个数，仅仅代表线程的ID。

最大并发数不要乱写（5以内），不要开太多，一般以2~3为宜，因为虽然任务是在子线程进行处理的，但是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.创建队列  NSOperationQueue *queue = [[NSOperationQueue alloc] init];  // 2.设置最大并发操作数(大并发操作数 = 1,就变成了串行队列)  queue.maxConcurrentOperationCount = 2;  // 3.添加操作  [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 --- 
    
     {number = 3, name = (null)}最大并发数[1909:113432] download1 --- 
     
      {number = 2, name = (null)}最大并发数[1909:113432] download4 --- 
      
       {number = 2, name = (null)}最大并发数[1909:113431] download3 --- 
       
        {number = 4, name = (null)}最大并发数[1909:113428] download5 --- 
        
         {number = 5, name = (null)}最大并发数[1909:113432] download6 --- 
         
          {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代表暂停队列，NO代表恢复队列）- (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。那么这种情况，就可以设置在用户操作UI（如滚动屏幕）的时候，暂停队列（不是取消队列），停止滚动的时候，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.创建队列  NSOperationQueue *queue = [[NSOperationQueue alloc] init];  // 2.设置最大并发操作数(大并发操作数 = 1,就变成了串行队列)  queue.maxConcurrentOperationCount = 1;  // 3.添加操作  [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 --- 
    
     {number = 3, name = (null)}队列的暂停和恢复[2650:156205] download2 --- 
     
      {number = 2, name = (null)}队列的暂停和恢复[2650:156206] download3 --- 
      
       {number = 3, name = (null)}队列的暂停和恢复[2650:156385] download4 --- 
       
        {number = 4, name = (null)}

4.3 队列的取消

取消队列的所有操作：相等于调用了所有 NSOperation 的 -(void)cancel 方法，

当前任务结束后，取消执行下面的所有任务，而非当前任务

// 也可调用NSOperation的 -(void)cancel 方法取消单个操作- (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.创建队列  NSOperationQueue *queue = [[NSOperationQueue alloc] init];  // 2.设置最大并发操作数(大并发操作数 = 1,就变成了串行队列)  queue.maxConcurrentOperationCount = 1;  // 3.添加操作  [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 - 取消队列的所有操作- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {  // 取消队列的所有操作（相等于调用了所有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 --- 
    
     {number = 3, name = (null)}队列的取消[3041:167749] download2 --- 
     
      {number = 2, name = (null)}

4.4 操作优先级

设置NSOperation在queue中的优先级，可以改变操作的执行优先级：

@property NSOperationQueuePriority queuePriority;- (void)setQueuePriority:(NSOperationQueuePriority)p;

优先级的取值：优先级高的任务，调用的几率会更大

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

4.5 操作依赖

NSOperation之间可以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）

// 操作B依赖于操作A（一定要让操作A执行完后，才能执行操作B）[operationB addDependency:operationA];

可以在不同queue的NSOperation之间创建依赖关系（跨队列依赖）：

注意：

一定要在把操作添加到队列之前，进行设置操作依赖。

任务添加的顺序并不能够决定执行顺序，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];  //创建对象，封装操作  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]);  }];  //操作的监听  op5.completionBlock = ^{    NSLog(@"op5执行完毕---%@", [NSThread currentThread]);  };  //设置操作依赖（op4执行完，才执行 op3）  [op3 addDependency:op1];  [op3 addDependency:op2];  [op3 addDependency:op4];  //把操作添加到队列中  [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：

操作依赖[4196:150518] download5----
    
     {number = 3, name = (null)}操作依赖[4196:150506] download1----
     
      {number = 4, name = (null)}操作依赖[4196:150509] download4----
      
       {number = 2, name = (null)}操作依赖[4196:150510] download2----
       
        {number = 5, name = (null)}操作依赖[4196:150518] op5执行完毕---
        
         {number = 3, name = (null)}操作依赖[4196:150509] download4----
         
          {number = 2, name = (null)}操作依赖[4196:150509] download4----
          
           {number = 2, name = (null)}操作依赖[4196:150509] download4----
           
            {number = 2, name = (null)}操作依赖[4196:150509] download4----
            
             {number = 2, name = (null)}操作依赖[4196:150509] download3----
             
              {number = 2, name = (null)}

操作的监听

可以监听一个操作的执行完毕：

@property (nullable, copy) void (^completionBlock)(void);- (void)setCompletionBlock:(void (^)(void))block;

代码详见4.5 操作依赖示例代码

5.0 线程间通信（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 - 线程间通信（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;    }];  }];  // 设置依赖操作  [combine addDependency:download1];  [combine addDependency:download2];  //把操作添加到队列中  [queue addOperation:download1];  [queue addOperation:download2];  [queue addOperation:combine];}#pragma mark - 线程间通信（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：

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

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.创建队列  NSOperationQueue *queue = [[NSOperationQueue alloc] init];  // 2.创建自定义 TDGOperation  TDOperation *op = [[TDOperation alloc] init];  // 3.把操作（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 
    
     @interface TDOperation : NSOperation@end

TDOperation.m

#import "TDOperation.h"@implementation TDOperation//需要执行的任务- (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作，如果执行取消操作，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作，如果执行取消操作，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作，如果执行取消操作，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-- 
    
     {number = 2, name = (null)}自定义NSOperation[1567:84075] download1 -1-- 
     
      {number = 2, name = (null)}自定义NSOperation[1567:84075] download1 -2-- 
      
       {number = 2, name = (null)}自定义NSOperation[1567:84075] download2 -0-- 
       
        {number = 2, name = (null)}自定义NSOperation[1567:84075] download2 -1-- 
        
         {number = 2, name = (null)}自定义NSOperation[1567:84075] download2 -2-- 
         
          {number = 2, name = (null)}自定义NSOperation[1567:84075] download3 -0-- 
          
           {number = 2, name = (null)}自定义NSOperation[1567:84075] download3 -1-- 
           
            {number = 2, name = (null)}自定义NSOperation[1567:84075] download3 -2-- 
            
             {number = 2, name = (null)}

6.1 自定义NSOperation队列的取消操作

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.创建队列  NSOperationQueue *queue = [[NSOperationQueue alloc] init];  // 2.设置最大并发操作数(大并发操作数 = 1,就变成了串行队列)  queue.maxConcurrentOperationCount = 2;  // 3.添加操作 - 自定义 NSOperation  [queue addOperation:[[TDOperation alloc] init]];  self.queue = queue;}#pragma mark - 取消队列的所有操作- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {  // 取消队列的所有操作（相等于调用了所有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 
    
     @interface TDOperation : NSOperation@end

TDOperation.m

#import "TDOperation.h"@implementation TDOperation//需要执行的任务- (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作，如果执行取消操作，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作，如果执行取消操作，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作，如果执行取消操作，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;                   //所有数据@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; //所有的操作对象@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）获得Library/Caches文件夹    NSString *cachesPath = [NSSearchPathForDirectoriesInDomains(        NSCachesDirectory, NSUserDomainMask, YES) firstObject];    //（2）获得文件名    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作      NSOperation *operation = self.operations[app.icon];      if (operation == nil) {        // 如果这张图片暂时没有下载操作，则需要创建一个下载操作        // 下载图片是耗时操作，放到子线程        operation = [NSBlockOperation blockOperationWithBlock:^{          // 下载图片          NSData *data =              [NSData dataWithContentsOfURL:[NSURL URLWithString:app.icon]];          // 如果数据下载失败          if (data == nil) {            // 下载失败，移除操作            [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，移除操作          [self.operations removeObjectForKey:app.icon];        }];        // 添加到队列中（队列的操作不需要移除，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 
    
     @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;                   //所有数据@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; //所有的操作对象@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 表示什么都不做      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 
    
     @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