技术文章iOSiOS面试那些事

iOS NSOperation

2015-11-12  本文已影响2470人  iOS_成才录

一、简介

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

二、NSOperation

1、使用NSOperation子类的方式有3种

1.1 NSInvocationOperation

-(id)initWithTarget:(id)target selector:(SEL)selector object:(id)arg;
// 一旦执行操作,就会调用target的selector方法
-(void)start;
  + 只有将NSOperation操作任务放到一个NSOperationQueue中,才会异步执行操作
- (void)invocation
{    
    // 1.将操作封装到Operation中
    NSInvocationOperation *op1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(demo) object:nil];
    // 2.执行封装的操作
    // 如果直接执行NSInvocationOperation中的操作, 那么默认会在主线程中执行
    [op1 start];
    
    NSInvocationOperation *op2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(test) object:nil];
    [op2 start];
}

1.2 NSBlockOperation

+(id)blockOperationWithBlock:(void(^)(void))block;
-(void)addExecutionBlock:(void(^)(void))block;
- (void)blockOperation
{
    // 1.封装操作
    NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"1- %@", [NSThread currentThread]);
    }];
    
    // 2.添加操作
    [op1 addExecutionBlock:^{
        NSLog(@"2- %@", [NSThread currentThread]);
    }];
    [op1 addExecutionBlock:^{
        NSLog(@"3- %@", [NSThread currentThread]);
    }];
    
    // 2.执行操作
    // 如果只封装了一个操作, 那么默认会在主线程中执行
    // 如果封装了多个操作, 那么除了第一个操作以外, 其它的操作会在子线程中执行
    [op1 start];
}

1.3 自定义 NSOperation,继承NSOperation

#import <Foundation/Foundation.h>
@interface JPOperation : NSOperation

@end

#import "JPOperation.h"

@implementation JPOperation

// 我们要重写main方法,封装操作
- (void)main
{
    NSLog(@"%s, %@", __func__,[NSThread currentThread]);
}
@end
    // 1.封装操作
    JPOperation *op1 = [[JPOperation alloc] init];
    // 2.执行操作
    [op1 start];
    
    JPOperation *op2 = [[JPOperation alloc] init];
    [op2 start];

三、NSOperationQueue

-(void)addOperation:(NSOperation*)op;
-(void)addOperationWithBlock:(void(^)(void))block;

基本使用

#import "ViewController.h"
#import "JPOperation.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // 1.创建队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    // 2.封装任务
    JPOperation *op1 = [[JPOperation alloc] init];
    JPOperation *op2 = [[JPOperation alloc] init];
    
    // 3.将任务添加到队列中
    [queue addOperation:op1];
    [queue addOperation:op2];
}

- (void)block
{
    // 1.创建队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];

    // 2.将任务添加到队列中
    // addOperationWithBlock方法会做两件事情
    // 1.根据传入的block, 创建一个NSBlockOperation对象
    // 2.将内部创建好的NSBlockOperation对象, 添加到队列中
    [queue addOperationWithBlock:^{
        NSLog(@"1 = %@", [NSThread currentThread]);
    }];
    [queue addOperationWithBlock:^{
        NSLog(@"2 = %@", [NSThread currentThread]);
    }];
}

- (void)invation
{
    /*
     GCD队列:
     串行: 自己创建, 主队列
     并发: 自己创建, 全局
     
     NSOperationQueue:
     自己创建: alloc/init --> 默认是并发 --> 也可以让它串行
     主队列  : mainQueue
     */
    // 1.创建队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    //    NSOperationQueue *queue = [NSOperationQueue mainQueue];
    
    // 2.封装任务
    NSInvocationOperation *op1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(demo) object:nil];
    NSInvocationOperation *op2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(test) object:nil];
    
    // 3.将任务添加到队列中
    // 只要将一个任务添加到alloc/init的队列中, 那么队列内部会自动调用start
    // 只要将一个任务添加到alloc/init的队列中, 就会开启一个新的线程执行队列
    [queue addOperation:op1];
    [queue addOperation:op2];
}

- (void)demo
{
    NSLog(@"demo = %@", [NSThread currentThread]);
}
- (void)test
{
    NSLog(@"test = %@", [NSThread currentThread]);
}
@end

四、NSOperatinoQueue的串行和并发 : 最大并发数

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // 1.创建队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init
                               ];
    // maxConcurrentOperationCount 默认等于 -1, 代表不限制, 可以创建N多线程
    // 默认就是并发
    // 如果想实现串行, 那么就设置maxConcurrentOperationCount = 1
    // 注意: 最大并发数, 不能设置为0, 否则任务不会被执行 \
    如果想再主线程中执行任务, 那么直接创建mainQueu即可
//    queue.maxConcurrentOperationCount = 1;
    
    // 2.创建任务
    NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"1 = %@", [NSThread currentThread]);
    }];
    NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"2 = %@", [NSThread currentThread]);
    }];
    NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1];
        NSLog(@"3 = %@", [NSThread currentThread]);
    }];
    
    // 3.将任务添加到队列中
    [queue addOperation:op1];
    [queue addOperation:op2];
    [queue addOperation:op3];   
}
@end

五、NSOperationQueue的暂停-恢复-取消

1、取消队列的所有操作

-(void)cancelAllOperations;

2、暂停和恢复队列

-(void)setSuspended:(BOOL)b;//如果是YES, 代表需要暂停,NO代表代表不需要暂停 ==  恢复执行
-(BOOL)isSuspended;

六、NSOperationQueue线程间通信

实例程序:开启子线程下载图片,下载好图片后,回到主线程进行更新UI

#import "ViewController.h"

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

@end

@implementation ViewController

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    // 1.开启子线程下载图片
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [queue addOperationWithBlock:^{
     // 子线程
        NSString *urlStr = @"https://www.baidu.com/img/bd_logo1.png";
    // url中文编码,防止乱码
    // urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        NSURL *url = [NSURL URLWithString:urlStr];
        NSData *data = [NSData dataWithContentsOfURL:url];
        // 2.生成下载好的图片
        UIImage *image = [UIImage imageWithData:data];
        
        // 3.回到主线程更新UI
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            NSLog(@"更新UI");
           // 主线程
            self.imageView.image = image;
        }];
    }];
}
@end

七、操作依赖

[operationB addDependency:operationA];// 操作B依赖于操作A , A操作执行完才会执行操作B


+ 2、除了同一quere操作间建立依赖关系,当然也可以在不同queue的NSOperation之间创建依赖关系

+ 注意点:
- 不能相互依赖 -> 比如A依赖B,B依赖A

> 经典实例:合成图片

```objc
#import "ViewController.h"

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

@end

@implementation ViewController
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
 NSOperationQueue *queue = [[NSOperationQueue alloc] init];
 NSOperationQueue *queue2 = [[NSOperationQueue alloc] init];
 
 __block UIImage *image1 = nil;
 __block UIImage *image2 = nil;
 // 1.开启一个线程下载第一张图片
 NSOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
     NSURL *url = [NSURL URLWithString:@"http://cdn.cocimg.com/assets/images/logo.png?v=201510272"];
     NSData *data = [NSData dataWithContentsOfURL:url];
     // 2.生成下载好的图片
     UIImage *image = [UIImage imageWithData:data];
     image1 = image;
 }];
 
 // 2.开启一个线程下载第二长图片
 NSOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
     NSURL *url = [NSURL URLWithString:@"https://www.baidu.com/img/bd_logo1.png"];
     NSData *data = [NSData dataWithContentsOfURL:url];
     // 2.生成下载好的图片
     UIImage *image = [UIImage imageWithData:data];
     image2 = image;
     
 }];
 // 3.开启一个线程合成图片
 NSOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
     UIGraphicsBeginImageContext(CGSizeMake(200, 200));
     [image1 drawInRect:CGRectMake(0, 0, 100, 200)];
     [image2 drawInRect:CGRectMake(100, 0, 100, 200)];
     UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();
     
     // 4.回到主线程更新UI
     [[NSOperationQueue mainQueue] addOperationWithBlock:^{
         NSLog(@"回到主线程更新UI");
         self.imageView.image = newImage;
     }];
 }];
 
 
 // 监听任务是否执行完毕
 op1.completionBlock = ^{
     NSLog(@"第一张图片下载完毕");
 };
 op2.completionBlock = ^{
     NSLog(@"第二张图片下载完毕");
 };
 
 // 添加依赖
 // 只要添加了依赖, 那么就会等依赖的任务执行完毕, 才会执行当前任务
 // 注意:
 // 1.添加依赖, 不能添加循环依赖
 // 2.NSOperation可以跨队列添加依赖
 [op3 addDependency:op1];
 [op3 addDependency:op2];

 // 将任务添加到队列中
 [queue addOperation:op1];
 [queue addOperation:op2];
 [queue2 addOperation:op3];
}
@end
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