NSOperation的使用细节 [2]

这一节我们来写自定义nonconcurrent的operation，自定义nonconcurrent的operation很简单，重写main方法，之后处理好cancel事件即可。

在开始写nonconcurrent的operation之前，我们需要先了解几个关于NSOperationQueue的细节。

挂起操作

通常情况下，将操作添加到队列中是会立马执行的（如果没有设置队列的最大并发数目），将suspended设置成YES后会将没有执行的operation全部挂起。

NSOperationQueue无法重复添加NSOperation

并且，NSOperationQueue也无法移除已经添加的操作

NSOperationQueue的cancelAllOperations仅仅是将所有的NSOperation的isCancelled置位为YES而已（NSOperation自身的cancel操作也是将isCancelled设置成YES）

我们可以通过设置NSOperationQueue的maxConcurrentOperationCount来让操作按照添加顺序执行

注意哦，NSOperationQueue并不能将单个的NSOperation进行挂起操作，NSOperation自身也无法将自己暂停后再进行恢复操作，当NSOperation取消了之后，你再也无法对其进行恢复操作了，在NSOperationQueue上，你是无法实现的。

以下提供源码

//
//  NonconcurrentOperation.h
//  NSOperationExample
//
//  Created by YouXianMing on 15/9/4.
//  Copyright (c) 2015年 YouXianMing. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NonconcurrentOperation : NSOperation

@property (nonatomic, strong)           NSString  *urlString;
@property (nonatomic, strong, readonly) NSData    *netData;

@end

//
//  NonconcurrentOperation.m
//  NSOperationExample
//
//  Created by YouXianMing on 15/9/4.
//  Copyright (c) 2015年 YouXianMing. All rights reserved.
//

#import "NonconcurrentOperation.h"

@interface NonconcurrentOperation ()

@property (nonatomic, strong) NSData   *netData;
@property (nonatomic)         BOOL      isDone;

@end

@implementation NonconcurrentOperation

- (void)main {

    if ([self isCancelled] == YES || [self isDone] == YES) {

        return;
    }

    NSURL *url            = [NSURL URLWithString:_urlString];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    self.netData = [NSURLConnection sendSynchronousRequest:request
                                         returningResponse:nil
                                                     error:nil];
    if (self.netData) {

        self.isDone = YES;
    }

    [self showThread];
}

- (void)showThread {

    if ([NSThread currentThread].isMainThread == YES) {

        NSLog(@"Run in MainThread %@", self.name);

    } else {

        NSLog(@"Run in SubThread  %@", self.name);
    }
}

@end

//
//  ViewController.m
//  NSOperationExample
//
//  Created by YouXianMing on 15/9/4.
//  Copyright (c) 2015年 YouXianMing. All rights reserved.
//

#import "ViewController.h"
#import "NonconcurrentOperation.h"

@interface ViewController () {

    NonconcurrentOperation *operation1;
    NonconcurrentOperation *operation2;
}

@property (nonatomic, strong) NSOperationQueue *queue;

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    self.queue                             = [[NSOperationQueue alloc] init];
    self.queue.maxConcurrentOperationCount = 2;

    // 操作1
    operation1           = [[NonconcurrentOperation alloc] init];
    operation1.urlString = @"http://pic.cnblogs.com/avatar/607542/20150807105148.png";
    operation1.name      = @"operation1";

    // 操作2
    operation2           = [[NonconcurrentOperation alloc] init];
    operation2.urlString = @"http://pic.cnblogs.com/avatar/615197/20150505132152.png";
    operation2.name      = @"operation2";

    [self.queue addOperation:operation1];
    [self.queue addOperation:operation2];

    [self performSelector:@selector(event) withObject:nil afterDelay:1.f];
}

- (void)event {

    NSLog(@"%@", self.queue.operations);
}

@end