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4.4 多线程进阶篇<下>(NSOperation)

蓝田丶
 蓝田丶
发布于 2016/04/13 17:58
字数 5257
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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

  1. 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] ------<NSThread: 0x7f9cea507920>{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------<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 --- <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 --- <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 --- <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 --- <NSThread: 0x7fcc09543b40>{number = 3, name = (null)}
队列的取消[3041:167749] download2 --- <NSThread: 0x7fcc094505f0>{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----<NSThread: 0x7ffa61d177d0>{number = 3, name = (null)}
操作依赖[4196:150506] download1----<NSThread: 0x7ffa61ca6b90>{number = 4, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150510] download2----<NSThread: 0x7ffa61f0e800>{number = 5, name = (null)}
操作依赖[4196:150518] op5执行完毕---<NSThread: 0x7ffa61d177d0>{number = 3, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150509] download3----<NSThread: 0x7ffa61f0e470>{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 <Foundation/Foundation.h>

@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-- <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 <Foundation/Foundation.h>

@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 <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;                   //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 <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 队列类型的创建方式

GCD 队列类型的创建方式:

(1)并发队列:手动创建、全局

(2)串行队列:手动创建、主队列


NSOperationQueue的队列类型的创建方法:

(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)其他队列(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



作者:蓝田(Loto)

如有疑问,请发送邮件至 shorfng@126.com联系我。



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