NSOperation

NSOperation的作用

配合使用NSOperation和NSOperationQueue也能实现多线程编程

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NSOperationQueue中的NSOperation取出来
• 将取出的NSOperation封装的操作放到一条新线程中执行

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

使用NSOperation子类的方式有3种

1. NSInvocationOperation
2. NSBlockOperation
3. 自定义子类继承NSOperation，实现内部相应的方法

小技巧：任务完成之后可以调用completionBlock，来知道是否任务完成

NSBlockOperation *op5 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op5 -----------%@",[NSThread currentThread]);
}];
op5.completionBlock = ^{
NSLog(@"下载完毕");
};

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

- (void)start;

一旦执行操作，就会调用target的sel方法

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

    NSInvocationOperation *p1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(run) object:nil];
     NSInvocationOperation *p2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(run) object:nil];
    [p1 start];
    [p2 start];

NSBlockOperation

创建NSBlockOperation对象

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

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

NSBlockOperation *p1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"%@----",[NSThread currentThread]);
    }];

    [p1 addExecutionBlock:^{
        NSLog(@"%@----",[NSThread currentThread]);
    }];

    [p1 addExecutionBlock:^{
        NSLog(@"%@----",[NSThread currentThread]);
    }];

    [p1 start];

自定义子类继承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

#import "MyOperation.h"

@implementation MyOperation

-(void)main{
    NSLog(@"---6666-----%@",[NSThread currentThread]);
}

@end

------------------------------------------------------------------
    MyOperation *p4 = [[MyOperation alloc] init];

    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    queue.maxConcurrentOperationCount = 1;
    [queue addOperation:p4];

建议在耗时任务时添加if (self.isCancelled) return; 判断任务是否取消。

-(void)main{
    NSLog(@"---6666-----%@",[NSThread currentThread]);

    for (NSInteger i = 0; i < 10000; i++) {
        NSLog(@"---1-----%ld",(long)i);
        if (self.isCancelled) return;
    }

    for (NSInteger i = 0; i < 10000; i++) {
        NSLog(@"---2-----%ld",(long)i);
        if (self.isCancelled) return;
    }

    for (NSInteger i = 0; i < 10000; i++) {
        NSLog(@"---3-----%ld",(long)i);
        if (self.isCancelled) return;
    }
}

NSOperationQueue

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

添加操作到NSOperationQueue中

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

//相当于
- (void)addOperationWithBlock:(void (^)(void))block;

NSOperationQueue的队列类型

• 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
• 非主队列（其他队列）
  • [[NSOperationQueue alloc] init]
  • 同时包含了：串行、并发功能
  • 添加到这种队列中的任务（NSOperation），就会自动放到子线程中执行

示例

NSInvocationOperation *p1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(run) object:nil];
     NSInvocationOperation *p2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(run) object:nil];
    NSBlockOperation *p3 = [NSBlockOperation blockOperationWithBlock:^{
                NSLog(@"%@----",[NSThread currentThread]);
            }];

    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [queue addOperation:p1];
    [queue addOperation:p2];
    [queue addOperation:p3];

第二种在队列中创建任务的方法

NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    queue.maxConcurrentOperationCount = 1;
    [queue addOperationWithBlock:^{
        NSLog(@"%@----1",[NSThread currentThread]);
    }];

    [queue addOperationWithBlock:^{
        NSLog(@"%@----2",[NSThread currentThread]);
    }];

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

最大并发数

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

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

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

    MyOperation *p4 = [[MyOperation alloc] init];
    [p4 cancel];

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;

注意点：暂停任务的时候，正在执行的任务会继续执行到结束，然后暂停。

示例

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    queue.maxConcurrentOperationCount = 1;
    [queue addOperationWithBlock:^{
        NSLog(@"%@----1",[NSThread currentThread]);
        [NSThread sleepForTimeInterval:1];
    }];

    [queue addOperationWithBlock:^{
        NSLog(@"%@----2",[NSThread currentThread]);
        [NSThread sleepForTimeInterval:1];
    }];

    [queue addOperationWithBlock:^{
        NSLog(@"%@----3",[NSThread currentThread]);
        [NSThread sleepForTimeInterval:1];
    }];

    [queue addOperationWithBlock:^{
        NSLog(@"%@----4",[NSThread currentThread]);
        [NSThread sleepForTimeInterval:1];
    }];

    [queue addOperationWithBlock:^{
        NSLog(@"%@----5",[NSThread currentThread]);
        [NSThread sleepForTimeInterval:1];
    }];

    _queue = queue;
}

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    if (self.queue.isSuspended) {
        self.queue.suspended = NO;
    }else{
        self.queue.suspended = YES;
    }
}

操作依赖

• 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

可以在不同queue的NSOperation之间创建依赖关系

NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"op1 -----------%@",[NSThread currentThread]);
    }];

    NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"op2 -----------%@",[NSThread currentThread]);
    }];

    NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"op3 -----------%@",[NSThread currentThread]);
    }];

    NSBlockOperation *op4 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"op4 -----------%@",[NSThread currentThread]);
    }];

    NSBlockOperation *op5 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"op5 -----------%@",[NSThread currentThread]);
    }];

    [op1 addDependency:op4];
    [op3 addDependency:op1];

    [queue1 addOperation:op1];
    [queue1 addOperation:op2];
    [queue1 addOperation:op3];

    [queue2 addOperation:op4];
    [queue2 addOperation:op5];

操作的监听

可以监听一个操作的执行完毕

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

线程间的通信

下载图片，回到主线程显示图片

 [[[NSOperationQueue alloc] init] addOperationWithBlock:^{
        NSURL *url = [NSURL URLWithString:@"https://cn.bing.com/sa/simg/CN_Logo_Gray.png"];

        NSData *data =[NSData dataWithContentsOfURL:url];

        UIImage *image = [UIImage imageWithData:data];

        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            self.imageView.image = image;
        }];
    }];

图片合成

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

    __block UIImage *image1 = nil;
    NSBlockOperation *download1 = [NSBlockOperation blockOperationWithBlock:^{
        NSURL *url = [NSURL URLWithString:@"https://cn.bing.com/sa/simg/CN_Logo_Gray.png"];

        NSData *data =[NSData dataWithContentsOfURL:url];

        image1 = [UIImage imageWithData:data];
    }];

    __block UIImage *image2 = nil;
    NSBlockOperation *download2 = [NSBlockOperation blockOperationWithBlock:^{
        NSURL *url = [NSURL URLWithString:@"https://cn.bing.com/sa/simg/CN_Logo_Gray.png"];

        NSData *data =[NSData dataWithContentsOfURL:url];

        image2 = [UIImage imageWithData:data];
    }];

    NSBlockOperation *com = [NSBlockOperation blockOperationWithBlock:^{
        //开启图片上下文
        UIGraphicsBeginImageContext(CGSizeMake(100, 100));

        [image1 drawInRect:CGRectMake(0, 0, 75, 150)];
        image1 = nil;
        [image2 drawInRect:CGRectMake(75, 0, 75, 150)];
        image2 = nil;

        UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

        UIGraphicsEndImageContext();

        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            self.imageView.image = image;
        }];
    }];

    [com addDependency:download1];
    [com addDependency:download2];

    [queue addOperation:download1];
    [queue addOperation:download2];
    [queue addOperation:com];