多线程开发之一 NSThread

每个 iOS 应用程序都有个专门用来更新显示 UI 界面、处理用户的触摸事件的主线程，因此不能将其他太耗时的操作放在主线程中执行，不然会造成主线程堵塞（出现卡机现象），带来不好的用户体验。

一般的解决方案就是：将那些耗时的操作放到另外一个线程中去执行，多线程编程就是防止主线程堵塞和增加运行效率的最佳方法。

iOS 支持多个层次的多线程编程，层次越高的抽象程度越高，使用也越方便，也是 Apple 最推荐使用的方法。

​下面根据抽象层次从低到高依次列出 iOS 所支持的多线程编程方法：

1. NSThread ：是三种方法里面相对轻量级的，但需要管理线程的生命周期、同步、加锁问题，这会导致一定的性能开销

2. NSOperation：是基于 OC 实现的，NSOperation 以面向对象的方式封装了需要执行的操作，不必关心线程管理、同步等问题。

   NSOperation 是一个抽象基类，iOS 提供了两种默认实现：NSInvocationOperation 和 NSBlockOperation，当然也可以自定义 NSOperation

3. Grand Central Dispatch(简称 GCD ，iOS4 才开始支持)：提供了一些新特性、运行库来支持多核并行编程，他的关注点更高：如何在多个 CPU 上提升效率

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"
 #import "ThirdSampleViewController.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 = @"多线程开发之一 NSThread";
         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;
         }
         case : {
             ThirdSampleViewController *thirdSampleVC = [ThirdSampleViewController new];
             [self.navigationController pushViewController:thirdSampleVC animated:YES];
             break;

             /*
              类似堆栈的先进后出的原理：
              返回到（上一级）、（任意级）、（根级）导航
             [self.navigationController popViewControllerAnimated:YES];
             [self.navigationController popToViewController:thirdSampleVC animated:YES];
             [self.navigationController popToRootViewControllerAnimated:YES];
              */
         }
         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

KMImageData.h

 #import <Foundation/Foundation.h>

 @interface KMImageData : NSObject
 @property (assign, nonatomic) NSInteger index;
 @property (strong, nonatomic) NSData *data;

 - (instancetype)initWithData:(NSData *)data withIndex:(NSInteger)index;

 @end

KMImageData.m

 #import "KMImageData.h"

 @implementation KMImageData

 - (instancetype)initWithData:(NSData *)data withIndex:(NSInteger)index {
     if (self = [super init]) {
         _data = data;
         _index = index;
     }
     return self;
 }

 @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"

 @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 * 150.0 / 190.0;
     _rescaleImageSize = CGSizeMake(width, height);

     //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 = [NSURL URLWithString:@"http://images.apple.com/v/macbook/c/overview/images/hero_static_large.jpg"];
     NSData *data = [NSData dataWithContentsOfURL:url];

     /*将数据显示到UI控件，注意只能在主线程中更新UI；
      另外 performSelectorOnMainThread 方法是 NSObject 的分类方法，每个 NSObject 对象都有此方法；
      它调用的 selector 方法是当前调用控件的方法，例如使用 UIImageView 调用的时候 selector 就是 UIImageView 的方法
      withObject：代表调用方法的参数，不过只能传递一个参数（如果有多个参数请使用对象进行封装）
      waitUntilDone：是否线程任务完成执行
      */
     [self performSelectorOnMainThread:@selector(updateImage:)
                            withObject:data
                         waitUntilDone:YES];
 }

 - (IBAction)loadImage:(id)sender {
     //方法一：使用线程对象实例方法创建一个线程
     //NSThread *thread = [[NSThread alloc] initWithTarget:self
     //                                           selector:@selector(loadImageFromNetwork)
     //                                             object:nil];
     //[thread start]; //启动一个线程；注意启动一个线程并非就一定立即执行，而是处于就绪状态，当系统调度时才真正执行

     //方法二：使用线程类方法创建一个线程
     [NSThread detachNewThreadSelector:@selector(loadImageFromNetwork)
                              toTarget:self
                            withObject:nil];
 }

 @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 "KMImageData.h"
 #import "UIImage+RescaleImage.h"

 #define kRowCount 4
 #define kColumnCount 3
 #define kCellSpacing 10.0

 @interface SecondSampleViewController ()
 - (void)layoutUI;
 - (void)updateImage:(KMImageData *)imageData;
 -(KMImageData *)requestData:(NSInteger)imageIndex;
 - (void)loadImageFromNetwork:(NSNumber *)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:(KMImageData *)imageData {
     UIImage *img = [UIImage imageWithData:imageData.data];
     UIImageView *imgVCurrent = _mArrImageView[imageData.index];
     imgVCurrent.image = [img rescaleImageToSize:_rescaleImageSize];
 }

 -(KMImageData *)requestData:(NSInteger)imageIndex {
     //对于多线程操作，建议把线程操作放到 @autoreleasepool 中
     @autoreleasepool {
         if (imageIndex != kRowCount * kColumnCount - ) { //虽然设置了最后一个线程的优先级为1.0，但无法保证他是第一个加载的。所以我们这里让其他线程挂起0.5秒，这样基本能保证最后一个线程第一个加载，除非网络非常差的情况
             [NSThread sleepForTimeInterval:0.5];
         }

         NSURL *url = [NSURL URLWithString:@"http://images.apple.com/v/macbook/c/overview/images/hero_static_large.jpg"];
         NSData *data = [NSData dataWithContentsOfURL:url];
         KMImageData *imageData = [[KMImageData alloc] initWithData:data
                                                          withIndex:imageIndex];
         return imageData;
     }
 }

 - (void)loadImageFromNetwork:(NSNumber *)imageIndex {
     NSLog(@"Current thread:%@",[NSThread currentThread]);

     /*将数据显示到UI控件，注意只能在主线程中更新UI；
      另外 performSelectorOnMainThread 方法是 NSObject 的分类方法，每个 NSObject 对象都有此方法；
      它调用的 selector 方法是当前调用控件的方法，例如使用 UIImageView 调用的时候 selector 就是 UIImageView 的方法
      withObject：代表调用方法的参数，不过只能传递一个参数（如果有多个参数请使用对象进行封装）
      waitUntilDone：是否线程任务完成执行
      */
     [self performSelectorOnMainThread:@selector(updateImage:)
                            withObject:[self requestData:[imageIndex integerValue]]
                         waitUntilDone:YES];
 }

 - (IBAction)loadImage:(id)sender {
     for (NSUInteger i=, len=kRowCount * kColumnCount; i<len; i++) {
         NSThread *thread = [[NSThread alloc] initWithTarget:self
                                                    selector:@selector(loadImageFromNetwork:)
                                                      object:[NSNumber numberWithInteger:i]];
         thread.name = [NSString stringWithFormat:@"Thread %lu", (unsigned long)i];
         thread.threadPriority = i == len- ? 1.0 : 0.0; //设置线程优先级；0.0-1.0，值越高优先级越高，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。因为首先其他线程是先启动的，其次网络状况我们没办法修改
         [thread start];
     }
 }

 @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>

ThirdSampleViewController.h

 #import <UIKit/UIKit.h>

 @interface ThirdSampleViewController : UIViewController
 @property (assign, nonatomic) CGSize rescaleImageSize;
 @property (strong, nonatomic) NSMutableArray *mArrImageView;
 @property (strong, nonatomic) NSMutableArray *mArrThread;

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

 @end

ThirdSampleViewController.m

 #import "ThirdSampleViewController.h"
 #import "KMImageData.h"
 #import "UIImage+RescaleImage.h"

 #define kRowCount 4
 #define kColumnCount 3
 #define kCellSpacing 10.0

 @interface ThirdSampleViewController ()
 - (void)layoutUI;
 - (void)updateImage:(KMImageData *)imageData;
 -(KMImageData *)requestData:(NSInteger)imageIndex;
 - (void)loadImageFromNetwork:(NSNumber *)imageIndex;
 @end

 @implementation ThirdSampleViewController

 - (void)viewDidLoad {
     [super viewDidLoad];

     [self layoutUI];
 }

 - (void)didReceiveMemoryWarning {
     [super didReceiveMemoryWarning];
     // Dispose of any resources that can be recreated.
 }

 - (void)dealloc {
     _mArrImageView = nil;
     _mArrThread = 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];
         }
     }

     void (^beautifulButton)(UIButton *, UIColor *) = ^(UIButton *btn, UIColor *tintColor) {
         btn.tintColor = tintColor;
         btn.layer.masksToBounds = YES;
         btn.layer.cornerRadius = 10.0;
         btn.layer.borderColor = [UIColor grayColor].CGColor;
         btn.layer.borderWidth = 1.0;
     };

     beautifulButton(_btnLoadImage, [UIColor darkGrayColor]);
     beautifulButton(_btnStopLoadImage, [UIColor redColor]);
 }

 - (void)updateImage:(KMImageData *)imageData {
     UIImage *img = [UIImage imageWithData:imageData.data];
     UIImageView *imgVCurrent = _mArrImageView[imageData.index];
     imgVCurrent.image = [img rescaleImageToSize:_rescaleImageSize];
 }

 -(KMImageData *)requestData:(NSInteger)imageIndex {
     //对于多线程操作，建议把线程操作放到 @autoreleasepool 中
     @autoreleasepool {
         if (imageIndex != kRowCount * kColumnCount - ) { //虽然设置了最后一个线程的优先级为1.0，但无法保证他是第一个加载的。所以我们这里让其他线程挂起0.5秒，这样基本能保证最后一个线程第一个加载，除非网络非常差的情况
             [NSThread sleepForTimeInterval:0.5];
         }

         NSURL *url = [NSURL URLWithString:@"http://images.apple.com/v/macbook/c/overview/images/hero_static_large.jpg"];
         NSData *data = [NSData dataWithContentsOfURL:url];
         KMImageData *imageData = [[KMImageData alloc] initWithData:data
                                                          withIndex:imageIndex];
         return imageData;
     }
 }

 - (void)loadImageFromNetwork:(NSNumber *)imageIndex { //子线程中执行
     //线程状态：thread.isExecuting（是否执行中）、thread.isFinished（是否已完成）、thread.isCancelled（是否已取消）
     //thread.isMainThread（是否主线程）、[NSThread isMultiThreaded]（是否多线程）

     KMImageData *imageData = [self requestData:[imageIndex integerValue]];

     NSThread *thread = _mArrThread[[imageIndex integerValue]];
     if (thread.isCancelled) { //判断线程是否已经取消，如是就退出当前线程；这里注意需让 exit 操作有足够的时间进行占用资源的释放，否则有可能出现异常；比如 Demo 中：当点击「停止加载」按钮后，再次快速点击「加载网络图片」按钮
         NSLog(@"Current thread:%@ will be cancelled.", thread);
         [NSThread exit];
     } else {
 //        //在后台执行一个方法，本质就是重新创建一个线程来执行方法
 //        [self performSelectorInBackground:@selector(updateImage:) withObject:imageData];
 //
 //        /*将数据显示到UI控件，注意只能在主线程中更新UI；
 //         另外 performSelectorOnMainThread 方法是 NSObject 的分类方法，每个 NSObject 对象都有此方法；它调用的 selector 方法是当前调用控件的方法，例如使用 UIImageView 调用的时候 selector 就是 UIImageView 的方法
 //         withObject：代表调用方法的参数，不过只能传递一个参数（如果有多个参数请使用对象进行封装）
 //         waitUntilDone：是否线程任务完成后执行
 //         */
 //        [self performSelectorOnMainThread:@selector(updateImage:)
 //                               withObject:imageData
 //                            waitUntilDone:YES];

         @try {
             //在指定的线程上执行一个方法，需要用户创建一个线程对象实例
             [self performSelector:@selector(updateImage:)
                          onThread:thread
                        withObject:imageData
                     waitUntilDone:YES];
         }
         @catch (NSException *exception) {
             NSLog(@"Exception: %@", [exception description]);
         }
     }
 }

 - (IBAction)loadImage:(id)sender {
     NSUInteger len = kRowCount * kColumnCount;
     _mArrThread = [NSMutableArray arrayWithCapacity:len];

     //循环创建多个线程
     for (NSUInteger i=; i<len; i++) {
         NSThread *thread = [[NSThread alloc] initWithTarget:self
                                                    selector:@selector(loadImageFromNetwork:)
                                                      object:[NSNumber numberWithInteger:i]];
         thread.name = [NSString stringWithFormat:@"Thread %lu", (unsigned long)i];
         thread.threadPriority = i == len- ? 1.0 : 0.0; //设置线程优先级；0.0-1.0，值越高优先级越高，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。因为首先其他线程是先启动的，其次网络状况我们没办法修改
         [_mArrThread addObject:thread];
     }

     //循环启动线程
     for (NSUInteger i=; i<len; i++) {
         NSThread *thread = _mArrThread[i];
         [thread start];
     }
 }

 - (IBAction)stopLoadImage:(id)sender { //主线程中执行
     for (NSUInteger i=, len=kRowCount * kColumnCount; i<len; i++) {
         NSThread *thread = _mArrThread[i];
         if (!thread.isFinished) { //判断线程是否完成，如果没有完成则设置为取消状态；取消状态仅仅是改变了线程状态而言，并不能终止线程
             [thread cancel];
         }
     }
 }

 @end

ThirdSampleViewController.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="ThirdSampleViewController">
             <connections>
                 <outlet property="btnLoadImage" destination="F5h-ZI-gGL" id="I40-e2-bAa"/>
                 <outlet property="btnStopLoadImage" destination="gnu-KE-bGq" id="tOA-t9-OA9"/>
                 <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="20" y="530" width="130" height="50"/>
                     <constraints>
                         <constraint firstAttribute="height" constant="50" id="HWd-Xc-Wk7"/>
                         <constraint firstAttribute="width" constant="130" 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>
                 <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="gnu-KE-bGq">
                     <rect key="frame" x="450" y="530" width="130" height="50"/>
                     <constraints>
                         <constraint firstAttribute="height" constant="50" id="1R7-22-hMk"/>
                         <constraint firstAttribute="width" constant="130" id="64l-yF-IFO"/>
                     </constraints>
                     <state key="normal" title="停止加载">
                         <color key="titleShadowColor" white="0.5" alpha="1" colorSpace="calibratedWhite"/>
                     </state>
                     <connections>
                         <action selector="loadImage:" destination="-1" eventType="touchUpInside" id="PyX-RW-cbL"/>
                         <action selector="stopLoadImage:" destination="-1" eventType="touchUpInside" id="1Xa-Ek-D4B"/>
                     </connections>
                 </button>
             </subviews>
             <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>
             <constraints>
                 <constraint firstItem="F5h-ZI-gGL" firstAttribute="leading" secondItem="i5M-Pr-FkT" secondAttribute="leading" constant="20" id="Glo-vW-SXd"/>
                 <constraint firstAttribute="trailing" secondItem="gnu-KE-bGq" secondAttribute="trailing" constant="20" id="IdF-1v-bg2"/>
                 <constraint firstAttribute="bottom" secondItem="gnu-KE-bGq" secondAttribute="bottom" constant="20" id="cyx-dg-K8M"/>
                 <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>
             <variation key="default">
                 <mask key="constraints">
                     <exclude reference="rH1-sV-pST"/>
                 </mask>
             </variation>
         </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）", @"请求多张网络图片（线程状态）"]];
     _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：

 -- ::38.945 NSThreadDemo[:]  INFO: Reveal Server started (Protocol Version ).
 -- ::57.863 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60cd1f80>{number = , name = Thread }
 -- ::57.863 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60c74800>{number = , name = Thread }
 -- ::57.863 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60cb8f30>{number = , name = Thread }
 -- ::57.863 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60cb8500>{number = , name = Thread }
 -- ::57.864 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60cd0c60>{number = , name = Thread }
 -- ::57.865 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60dee540>{number = , name = Thread }
 -- ::57.864 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60cd2150>{number = , name = Thread }
 -- ::57.866 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60daf730>{number = , name = Thread }
 -- ::57.866 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60db8530>{number = , name = Thread }
 -- ::57.866 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60f3f7e0>{number = , name = Thread }
 -- ::57.866 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60db2390>{number = , name = Thread }
 -- ::57.867 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60f231c0>{number = , name = Thread }

 -- ::07.073 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f63010930>{number = , name = Thread } will be cancelled.
 -- ::07.691 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60df0210>{number = , name = Thread } will be cancelled.
 -- ::07.697 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60db8ee0>{number = , name = Thread } will be cancelled.
 -- ::07.729 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60db2390>{number = , name = Thread } will be cancelled.
 -- ::07.857 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f63011190>{number = , name = Thread } will be cancelled.
 -- ::08.025 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f6300c2d0>{number = , name = Thread } will be cancelled.
 -- ::08.047 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60dd4200>{number = , name = Thread } will be cancelled.
 -- ::08.191 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60db8ee0>{number = , name = Thread } will be cancelled.
 -- ::08.250 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f630110b0>{number = , name = Thread } will be cancelled.
 -- ::08.416 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60df7bc0>{number = , name = Thread } will be cancelled.
 -- ::08.464 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60dc5ca0>{number = , name = Thread } will be cancelled.
 -- ::08.495 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f63011190>{number = , name = Thread } will be cancelled.
 -- ::08.661 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60df0210>{number = , name = Thread } will be cancelled.
 -- ::10.033 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f60da3330>{number = , name = Thread } will be cancelled.
 -- ::10.056 NSThreadDemo[:] Current thread:<NSThread: 0x7f9f63010930>{number = , name = Thread } will be cancelled.