多线程开发之二 NSOperation

效果如下：

ViewController.h

 #import <UIKit/UIKit.h>

 @interface ViewController : UITableViewController

 @property (copy, nonatomic) NSArray *arrSampleName;

 - (instancetype)initWithSampleNameArray:(NSArray *)arrSampleName;

 @end

ViewController.m

 #import "ViewController.h"

 #import "FirstSampleViewController.h"

 #import "SecondSampleViewController.h"

 @interface ViewController ()

 - (void)layoutUI;

 @end

 @implementation ViewController

 - (void)viewDidLoad {

     [super viewDidLoad];

     [self layoutUI];

 }

 - (void)didReceiveMemoryWarning {

     [super didReceiveMemoryWarning];

     // Dispose of any resources that can be recreated.

 }

 - (instancetype)initWithSampleNameArray:(NSArray *)arrSampleName {

     if (self = [super initWithStyle:UITableViewStyleGrouped]) {

         self.navigationItem.title = @"多线程开发之二 NSOperation";

         self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"返回首页" style:UIBarButtonItemStylePlain target:nil action:nil];

         _arrSampleName = arrSampleName;

     }

     return self;

 }

 - (void)layoutUI {

 }

 #pragma mark - UITableViewController相关方法重写

 - (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section {

     return 0.1;

 }

 - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {

     return ;

 }

 - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {

     return [_arrSampleName count];

 }

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

     static NSString *cellIdentifier = @"cell";

     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];

     if (!cell) {

         cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];

     }

     cell.textLabel.text = _arrSampleName[indexPath.row];

     return cell;

 }

 - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

     switch (indexPath.row) {

         case : {

             FirstSampleViewController *firstSampleVC = [FirstSampleViewController new];

             [self.navigationController pushViewController:firstSampleVC animated:YES];

             break;

         }

         case : {

             SecondSampleViewController *secondSampleVC = [SecondSampleViewController new];

             [self.navigationController pushViewController:secondSampleVC animated:YES];

             break;

         }

         default:

             break;

     }

 }

 @end

UIImage+RescaleImage.h

 #import <UIKit/UIKit.h>

 @interface UIImage (RescaleImage)

 /**

  *  根据宽高大小，获取对应的缩放图片

  *

  *  @param size 宽高大小

  *

  *  @return 对应的缩放图片

  */

 - (UIImage *)rescaleImageToSize:(CGSize)size;

 @end

UIImage+RescaleImage.m

 #import "UIImage+RescaleImage.h"

 @implementation UIImage (RescaleImage)

 - (UIImage *)rescaleImageToSize:(CGSize)size {

     CGRect rect = CGRectMake(0.0, 0.0, size.width, size.height);

     UIGraphicsBeginImageContext(rect.size);

     [self drawInRect:rect];

     UIImage *imgScale = UIGraphicsGetImageFromCurrentImageContext();

     UIGraphicsEndImageContext();

     return imgScale;

 }

 @end

Common.h

 #import <Foundation/Foundation.h>

 @interface Common : NSObject

 + (NSURL *)randomImageURL;

 @end

Common.m

 #import "Common.h"

 @implementation Common

 + (NSURL *)randomImageURL {

     NSUInteger randomVal = (arc4random() % ) + ; //1-20的随机数

     NSString *randomValStr = [NSString stringWithFormat:@"%lu", (unsigned long)randomVal];

     if (randomVal < ) {

         randomValStr = [@"" stringByAppendingString:randomValStr];

     }

     NSString *imageURLStr = [NSString stringWithFormat:@"http://images.apple.com/v/watch/e/apple-watch/images/collection_%@_large.jpg", randomValStr];

     return [NSURL URLWithString:imageURLStr];

 }

 @end

FirstSampleViewController.h

 #import <UIKit/UIKit.h>

 @interface FirstSampleViewController : UIViewController

 @property (assign, nonatomic) CGSize rescaleImageSize;

 @property (strong, nonatomic) IBOutlet UIImageView *imgV;

 @property (strong, nonatomic) IBOutlet UIButton *btnLoadImage;

 @end

FirstSampleViewController.m

 #import "FirstSampleViewController.h"

 #import "UIImage+RescaleImage.h"

 #import "Common.h"

 @interface FirstSampleViewController ()

 - (void)layoutUI;

 - (void)updateImage:(NSData *)imageData;

 - (void)loadImageFromNetwork;

 @end

 @implementation FirstSampleViewController

 - (void)viewDidLoad {

     [super viewDidLoad];

     [self layoutUI];

 }

 - (void)didReceiveMemoryWarning {

     [super didReceiveMemoryWarning];

     // Dispose of any resources that can be recreated.

 }

 - (void)dealloc {

     _imgV.image = nil;

 }

 - (void)layoutUI {

     CGFloat width = [[UIScreen mainScreen] bounds].size.width; //bounds 返回整个屏幕大小；applicationFrame 返回去除状态栏后的屏幕大小

     CGFloat height = width * 438.0 / 366.0;

     const CGFloat percentVal = 3.0 / 4.0; //以屏幕宽度的3/4比例显示

     _rescaleImageSize = CGSizeMake(width * percentVal, height * percentVal);

     //NSString *path = [[NSBundle mainBundle] pathForResource:@"PictureNo@2x" ofType:@"png"];

     //_imgV.image = [UIImage imageWithContentsOfFile:path];

     _btnLoadImage.tintColor = [UIColor darkGrayColor];

     _btnLoadImage.layer.masksToBounds = YES;

     _btnLoadImage.layer.cornerRadius = 10.0;

     _btnLoadImage.layer.borderColor = [UIColor grayColor].CGColor;

     _btnLoadImage.layer.borderWidth = 1.0;

 }

 - (void)updateImage:(NSData *)imageData {

     UIImage *img = [UIImage imageWithData:imageData];

     _imgV.image = [img rescaleImageToSize:_rescaleImageSize];

 }

 - (void)loadImageFromNetwork {

     NSURL *url = [Common randomImageURL];

     NSData *data = [NSData dataWithContentsOfURL:url];

     //mainQueue 是 UI 主线程，调用主线程队列的方法进行操作

     [[NSOperationQueue mainQueue] addOperationWithBlock:^{

         [self updateImage:data];

     }];

 }

 - (IBAction)loadImage:(id)sender {

     //方法一：使用 NSInvocationOperation

 //    NSInvocationOperation *invocationOperation = [[NSInvocationOperation alloc]

 //                                                  initWithTarget:self

 //                                                  selector:@selector(loadImageFromNetwork)

 //                                                  object:nil];

 //    NSOperationQueue *operationQueue = [NSOperationQueue new]; //操作队列

 //    [operationQueue addOperation:invocationOperation];

     //方法二：使用 NSBlockOperation

     NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{

         [self loadImageFromNetwork];

     }];

     [blockOperation addExecutionBlock:^{ //还可以为 blockOperation 添加代码块；多个代码块会被分到多个线程去执行，存在两个代码块被分配到同一个线程执行的情况

         NSLog(@"代码块");

     }];

     [blockOperation addExecutionBlock:[blockOperation executionBlocks][]]; //这里可以调用他的 executionBlocks 获取到添加的代码块数组；上面打印的内容「代码块」会被执行两次

     [blockOperation setCompletionBlock:^{

         NSLog(@"所有代码块操作执行完毕后（无论已取消还是已完成），做一些事情，只执行一次");

     }];

     //[blockOperation start]; //使用 start 方法，则此操作在主线程中执行；一般不这样操作，而是添加到操作队列中

     NSOperationQueue *operationQueue = [NSOperationQueue new]; //操作队列

     [operationQueue addOperation:blockOperation]; //添加到操作队列，这时队列会开启一个线程去执行此操作；一个线程可以执行多个操作

     //方法三：直接使用 NSOperationQueue

 //    NSOperationQueue *operationQueue = [NSOperationQueue new]; //操作队列

 //    [operationQueue addOperationWithBlock:^{

 //        [self loadImageFromNetwork];

 //    }];

 }

 @end

FirstSampleViewController.xib

 <?xml version="1.0" encoding="UTF-8" standalone="no"?>

 <document type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="3.0" toolsVersion="7706" systemVersion="14E46" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES">

     <dependencies>

         <deployment identifier="iOS"/>

         <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="7703"/>

     </dependencies>

     <objects>

         <placeholder placeholderIdentifier="IBFilesOwner" id="-1" userLabel="File's Owner" customClass="FirstSampleViewController">

             <connections>

                 <outlet property="btnLoadImage" destination="sLs-f1-Gzc" id="kX8-J0-v0V"/>

                 <outlet property="imgV" destination="4Qp-uk-KAb" id="RM3-Ha-glh"/>

                 <outlet property="view" destination="i5M-Pr-FkT" id="sfx-zR-JGt"/>

             </connections>

         </placeholder>

         <placeholder placeholderIdentifier="IBFirstResponder" id="-2" customClass="UIResponder"/>

         <view clearsContextBeforeDrawing="NO" contentMode="scaleToFill" id="i5M-Pr-FkT">

             <rect key="frame" x="0.0" y="0.0" width="600" height="600"/>

             <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>

             <subviews>

                 <imageView userInteractionEnabled="NO" contentMode="scaleToFill" horizontalHuggingPriority="251" verticalHuggingPriority="251" image="PictureNo.png" translatesAutoresizingMaskIntoConstraints="NO" id="4Qp-uk-KAb">

                     <rect key="frame" x="205" y="225" width="190" height="150"/>

                     <constraints>

                         <constraint firstAttribute="height" constant="150" id="SIp-Wd-idU"/>

                         <constraint firstAttribute="height" constant="150" id="VwM-i1-atB"/>

                         <constraint firstAttribute="width" constant="190" id="mUh-Bu-tUd"/>

                         <constraint firstAttribute="width" constant="190" id="mdJ-1c-QFa"/>

                         <constraint firstAttribute="width" constant="190" id="sVS-bU-Ty9"/>

                         <constraint firstAttribute="height" constant="150" id="uMG-oN-J56"/>

                         <constraint firstAttribute="height" constant="150" id="vws-Qw-UrB"/>

                     </constraints>

                     <variation key="default">

                         <mask key="constraints">

                             <exclude reference="SIp-Wd-idU"/>

                             <exclude reference="VwM-i1-atB"/>

                             <exclude reference="mUh-Bu-tUd"/>

                             <exclude reference="mdJ-1c-QFa"/>

                             <exclude reference="sVS-bU-Ty9"/>

                             <exclude reference="uMG-oN-J56"/>

                             <exclude reference="vws-Qw-UrB"/>

                         </mask>

                     </variation>

                 </imageView>

                 <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="sLs-f1-Gzc">

                     <rect key="frame" x="230" y="500" width="140" height="50"/>

                     <constraints>

                         <constraint firstAttribute="width" constant="140" id="1jv-9K-mdH"/>

                         <constraint firstAttribute="height" constant="50" id="Q2w-vR-9ac"/>

                     </constraints>

                     <state key="normal" title="加载网络图片">

                         <color key="titleShadowColor" white="0.5" alpha="1" colorSpace="calibratedWhite"/>

                     </state>

                     <connections>

                         <action selector="loadImage:" destination="-1" eventType="touchUpInside" id="fdy-Ln-5oS"/>

                     </connections>

                 </button>

             </subviews>

             <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>

             <constraints>

                 <constraint firstItem="4Qp-uk-KAb" firstAttribute="leading" secondItem="i5M-Pr-FkT" secondAttribute="leading" constant="205" id="2a2-mS-WFa"/>

                 <constraint firstItem="sLs-f1-Gzc" firstAttribute="top" secondItem="i5M-Pr-FkT" secondAttribute="top" id="ES4-wl-RBz"/>

                 <constraint firstItem="4Qp-uk-KAb" firstAttribute="centerY" secondItem="i5M-Pr-FkT" secondAttribute="centerY" id="MUJ-WA-sUf"/>

                 <constraint firstItem="4Qp-uk-KAb" firstAttribute="centerX" secondItem="sLs-f1-Gzc" secondAttribute="centerX" id="Q8a-1k-DzJ"/>

                 <constraint firstAttribute="bottom" secondItem="4Qp-uk-KAb" secondAttribute="bottom" constant="71" id="V0a-9y-Dwa"/>

                 <constraint firstAttribute="bottom" secondItem="sLs-f1-Gzc" secondAttribute="bottom" constant="50" id="VMG-CV-eeq"/>

                 <constraint firstItem="4Qp-uk-KAb" firstAttribute="top" secondItem="i5M-Pr-FkT" secondAttribute="top" constant="-71" id="gqW-Wq-4Zv"/>

                 <constraint firstItem="sLs-f1-Gzc" firstAttribute="centerX" secondItem="i5M-Pr-FkT" secondAttribute="centerX" id="kNf-6d-EJ8"/>

             </constraints>

             <variation key="default">

                 <mask key="constraints">

                     <exclude reference="2a2-mS-WFa"/>

                     <exclude reference="V0a-9y-Dwa"/>

                     <exclude reference="gqW-Wq-4Zv"/>

                     <exclude reference="ES4-wl-RBz"/>

                 </mask>

             </variation>

         </view>

     </objects>

     <resources>

         <image name="PictureNo.png" width="190" height="150"/>

     </resources>

 </document>

SecondSampleViewController.h

 #import <UIKit/UIKit.h>

 @interface SecondSampleViewController : UIViewController

 @property (assign, nonatomic) CGSize rescaleImageSize;

 @property (strong, nonatomic) NSMutableArray *mArrImageView;

 @property (strong, nonatomic) IBOutlet UIButton *btnLoadImage;

 @end

SecondSampleViewController.m

 #import "SecondSampleViewController.h"

 #import "UIImage+RescaleImage.h"

 #import "Common.h"

 #define kRowCount 4

 #define kColumnCount 3

 #define kCellSpacing 10.0

 @interface SecondSampleViewController ()

 - (void)layoutUI;

 - (void)updateImage:(NSData *)imageData withImageIndex:(NSInteger)imageIndex;

 -(NSData *)requestData:(NSInteger)imageIndex;

 - (void)loadImageFromNetwork:(NSInteger)imageIndex;

 @end

 @implementation SecondSampleViewController

 - (void)viewDidLoad {

     [super viewDidLoad];

     [self layoutUI];

 }

 - (void)didReceiveMemoryWarning {

     [super didReceiveMemoryWarning];

     // Dispose of any resources that can be recreated.

 }

 - (void)dealloc {

     _mArrImageView = nil;

 }

 - (void)layoutUI {

     CGFloat width = ([[UIScreen mainScreen] bounds].size.width - ((kColumnCount + ) * kCellSpacing)) / kColumnCount;

     _rescaleImageSize = CGSizeMake(width, width);

     CGFloat heightOfStatusAndNav = 20.0 + 44.0;

     NSString *path = [[NSBundle mainBundle] pathForResource:@"PictureNo@2x" ofType:@"png"];

     UIImage *img = [UIImage imageWithContentsOfFile:path];

     _mArrImageView = [NSMutableArray arrayWithCapacity:kRowCount * kColumnCount];

     //初始化多个图片视图

     for (NSUInteger i=; i<kRowCount; i++) {

         for (NSUInteger j=; j<kColumnCount; j++) {

             UIImageView *imgV = [[UIImageView alloc] initWithFrame:

                                  CGRectMake(_rescaleImageSize.width * j + kCellSpacing * (j+),

                                             _rescaleImageSize.height * i + kCellSpacing * (i+) + heightOfStatusAndNav,

                                             _rescaleImageSize.width,

                                             _rescaleImageSize.height)];

             imgV.image = img;

             [self.view addSubview:imgV];

             [_mArrImageView addObject:imgV];

         }

     }

     _btnLoadImage.tintColor = [UIColor darkGrayColor];

     _btnLoadImage.layer.masksToBounds = YES;

     _btnLoadImage.layer.cornerRadius = 10.0;

     _btnLoadImage.layer.borderColor = [UIColor grayColor].CGColor;

     _btnLoadImage.layer.borderWidth = 1.0;

 }

 - (void)updateImage:(NSData *)imageData withImageIndex:(NSInteger)imageIndex {

     UIImage *img = [UIImage imageWithData:imageData];

     UIImageView *imgVCurrent = _mArrImageView[imageIndex];

     imgVCurrent.image = [img rescaleImageToSize:_rescaleImageSize];

 }

 -(NSData *)requestData:(NSInteger)imageIndex {

     //对于多线程操作，建议把线程操作放到 @autoreleasepool 中

     @autoreleasepool {

         NSURL *url = [Common randomImageURL];

         NSData *data = [NSData dataWithContentsOfURL:url];

         return data;

     }

 }

 - (void)loadImageFromNetwork:(NSInteger)imageIndex {

     /*

      对比之前 NSThread 加载图片，你会发现核心代码简化了不少，有两点值得提的：

      （1）使用 NSBlockOperation 方法，所有的操作不必单独定义方法，同时解决了只能传递一个参数的问题。类似的操作，例如：调用主线程队列的 addOperationWithBlock: 方法进行 UI 更新，不用再定义一个参数实体类来进行参数传递（之前必须定义一个 KMImageData 解决只能传递一个参数的问题）。

      （2）使用 NSOperation 进行多线程开发可以设置最大并发操作数，有效的对操作进行控制（如 Demo 的代码设置最大并发操作数为5，则图片最多是五个一次加载的）。

      */

     NSLog(@"Current thread:%@", [NSThread currentThread]);

     //mainQueue 是 UI 主线程，调用主线程队列的方法进行操作

     [[NSOperationQueue mainQueue] addOperationWithBlock:^{

         [self updateImage:[self requestData:imageIndex] withImageIndex:imageIndex];

     }];

 }

 - (IBAction)loadImage:(id)sender {

     NSOperationQueue *operationQueue = [NSOperationQueue new];

     operationQueue.maxConcurrentOperationCount = ; //设置最大并发操作数

     NSUInteger len = kRowCount * kColumnCount;

     NSBlockOperation *lastBlockOperation = [NSBlockOperation blockOperationWithBlock:^{

         [self loadImageFromNetwork:len - ];

     }];

     for (NSUInteger i=; i<len - ; i++) {

         NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{

             [self loadImageFromNetwork:i];

         }];

         //实现控制「操作执行顺序」，例如：控制最后一个操作第一个执行，这里设置操作的依赖关系为：最后一张图片加载操作完成后才执行

         //PS：注意请勿进行循环依赖，否则循环依赖相关的操作是不会被执行的

         //这里添加依赖关系；其相对应的移除方法：- (void)removeDependency:(NSOperation *)op;

         [blockOperation addDependency:lastBlockOperation];

         //另外添加操作对象实例数组的方法：- (void)addOperations:(NSArray *)ops waitUntilFinished:(BOOL)wait;

         [operationQueue addOperation:blockOperation];

     }

     [operationQueue addOperation:lastBlockOperation];

     /*

     lastBlockOperation.queuePriority = NSOperationQueuePriorityVeryHigh; //在某个操作队列中的队列优先级；这样可以提高他被优先加载的机率，但是他也未必就第一个加载；所以要实现控制「操作执行顺序」，就得用设置操作的依赖关系的方式

     typedef enum : NSInteger {

         NSOperationQueuePriorityVeryLow = -8,

         NSOperationQueuePriorityLow = -4,

         NSOperationQueuePriorityNormal = 0,

         NSOperationQueuePriorityHigh = 4,

         NSOperationQueuePriorityVeryHigh = 8

     } NSOperationQueuePriority;

      */

 }

 @end

SecondSampleViewController.xib

 <?xml version="1.0" encoding="UTF-8" standalone="no"?>

 <document type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="3.0" toolsVersion="7706" systemVersion="14E46" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES">

     <dependencies>

         <deployment identifier="iOS"/>

         <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="7703"/>

     </dependencies>

     <objects>

         <placeholder placeholderIdentifier="IBFilesOwner" id="-1" userLabel="File's Owner" customClass="SecondSampleViewController">

             <connections>

                 <outlet property="btnLoadImage" destination="F5h-ZI-gGL" id="I40-e2-bAa"/>

                 <outlet property="view" destination="i5M-Pr-FkT" id="sfx-zR-JGt"/>

             </connections>

         </placeholder>

         <placeholder placeholderIdentifier="IBFirstResponder" id="-2" customClass="UIResponder"/>

         <view clearsContextBeforeDrawing="NO" contentMode="scaleToFill" id="i5M-Pr-FkT">

             <rect key="frame" x="0.0" y="0.0" width="600" height="600"/>

             <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>

             <subviews>

                 <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="F5h-ZI-gGL">

                     <rect key="frame" x="230" y="530" width="140" height="50"/>

                     <constraints>

                         <constraint firstAttribute="height" constant="50" id="HWd-Xc-Wk7"/>

                         <constraint firstAttribute="width" constant="140" id="vrH-qE-PNK"/>

                     </constraints>

                     <state key="normal" title="加载网络图片">

                         <color key="titleShadowColor" white="0.5" alpha="1" colorSpace="calibratedWhite"/>

                     </state>

                     <connections>

                         <action selector="loadImage:" destination="-1" eventType="touchUpInside" id="Hgw-q8-lHy"/>

                     </connections>

                 </button>

             </subviews>

             <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>

             <constraints>

                 <constraint firstAttribute="bottom" secondItem="F5h-ZI-gGL" secondAttribute="bottom" constant="20" id="jPY-fY-9XJ"/>

                 <constraint firstAttribute="centerX" secondItem="F5h-ZI-gGL" secondAttribute="centerX" id="rH1-sV-pST"/>

             </constraints>

         </view>

     </objects>

 </document>

AppDelegate.h

 #import <UIKit/UIKit.h>

 @interface AppDelegate : UIResponder <UIApplicationDelegate>

 @property (strong, nonatomic) UIWindow *window;

 @property (strong, nonatomic) UINavigationController *navigationController;

 @end

AppDelegate.m

 #import "AppDelegate.h"

 #import "ViewController.h"

 @interface AppDelegate ()

 @end

 @implementation AppDelegate

 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

     _window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

     ViewController *viewController = [[ViewController alloc] initWithSampleNameArray:@[@"请求单张网络图片（解决线程阻塞）", @"请求多张网络图片（多个线程并发）"]];

     _navigationController = [[UINavigationController alloc] initWithRootViewController:viewController];

     _window.rootViewController = _navigationController;

     //[_window addSubview:_navigationController.view]; //当_window.rootViewController关联时，这一句可有可无

     [_window makeKeyAndVisible];

     return YES;

 }

 - (void)applicationWillResignActive:(UIApplication *)application {

 }

 - (void)applicationDidEnterBackground:(UIApplication *)application {

 }

 - (void)applicationWillEnterForeground:(UIApplication *)application {

 }

 - (void)applicationDidBecomeActive:(UIApplication *)application {

 }

 - (void)applicationWillTerminate:(UIApplication *)application {

 }

 @end

输出结果：

 -- ::36.878 NSOperationDemo[:] 代码块

 -- ::36.878 NSOperationDemo[:] 代码块

 -- ::37.366 NSOperationDemo[:] 所有代码块操作执行完毕后（无论已取消还是已完成），做一些事情，只执行一次

 -- ::42.505 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1bd335b0>{number = , name = (null)}

 -- ::42.506 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1be0ad90>{number = , name = (null)}

 -- ::42.507 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1e047390>{number = , name = (null)}

 -- ::42.507 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1e047390>{number = , name = (null)}

 -- ::42.507 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1be0ad90>{number = , name = (null)}

 -- ::42.507 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1be07c70>{number = , name = (null)}

 -- ::42.508 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1be0ad90>{number = , name = (null)}

 -- ::42.508 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1be07c70>{number = , name = (null)}

 -- ::42.508 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1be0ad90>{number = , name = (null)}

 -- ::42.508 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1e047390>{number = , name = (null)}

 -- ::42.508 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1e0335f0>{number = , name = (null)}

 -- ::42.508 NSOperationDemo[:] Current thread:<NSThread: 0x7fbd1be0ad90>{number = , name = (null)}

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