1 #import <UIKit/UIKit.h>2 3 @interface ViewController : UITableViewController4 @PRoperty (copy, nonatomic) NSArray *arrSampleName;5 6 - (instancetype)initWithSampleNameArray:(NSArray *)arrSampleName;7 8 @end

 1 #import "ViewController.h" 2 #import "FirstSampleViewController.h" 3 #import "SecondSampleViewController.h" 4  5 @interface ViewController () 6 - (void)layoutUI; 7 @end 8  9 @implementation ViewController10 - (void)viewDidLoad {11     [super viewDidLoad];12     13     [self layoutUI];14 }15 16 - (void)didReceiveMemoryWarning {17     [super didReceiveMemoryWarning];18     // Dispose of any resources that can be recreated.19 }20 21 - (instancetype)initWithSampleNameArray:(NSArray *)arrSampleName {22     if (self = [super initWithStyle:UITableViewStyleGrouped]) {23         self.navigationItem.title = @"多線程開發之三 GCD";24         self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"返回首頁" style:UIBarButtonItemStylePlain target:nil action:nil];25         26         _arrSampleName = arrSampleName;27     }28     return self;29 }30 31 - (void)layoutUI {32 }33 34 #pragma mark - UITableViewController相關方法重寫35 - (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section {36     return 0.1;37 }38 39 - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {40     return 1;41 }42 43 - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {44     return [_arrSampleName count];45 }46 47 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {48     static NSString *cellIdentifier = @"cell";49     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];50     if (!cell) {51         cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];52     }53     cell.textLabel.text = _arrSampleName[indexPath.row];54     return cell;55 }56 57 - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {58     switch (indexPath.row) {59         case 0: {60             FirstSampleViewController *firstSampleVC = [FirstSampleViewController new];61             [self.navigationController pushViewController:firstSampleVC animated:YES];62             break;63         }64         case 1: {65             SecondSampleViewController *secondSampleVC = [SecondSampleViewController new];66             [self.navigationController pushViewController:secondSampleVC animated:YES];67             break;68         }69         default:70             break;71     }72 }73 74 @end

 1 #import <UIKit/UIKit.h> 2  3 @interface UIImage (RescaleImage) 4 /** 5  *  根據寬高大小，獲取對應的縮放圖片 6  * 7  *  @param size 寬高大小 8  * 9  *  @return 對應的縮放圖片10  */11 - (UIImage *)rescaleImageToSize:(CGSize)size;12 13 @end 

 1 #import "UIImage+RescaleImage.h" 2  3 @implementation UIImage (RescaleImage) 4  5 - (UIImage *)rescaleImageToSize:(CGSize)size { 6     CGRect rect = CGRectMake(0.0, 0.0, size.width, size.height); 7      8     UIGraphicsBeginImageContext(rect.size); 9     [self drawInRect:rect];10     UIImage *imgScale = UIGraphicsGetImageFromCurrentImageContext();11     UIGraphicsEndImageContext();12     13     return imgScale;14 }15 16 @end

1 #import <Foundation/Foundation.h>2 3 @interface Common : NSObject4 + (NSURL *)randomImageURL;5 6 @end 

 1 #import "Common.h" 2  3 static NSArray *arrPartOfURL = nil; 4 @implementation Common 5  6 + (NSURL *)randomImageURL { 7     if (arrPartOfURL == nil) { 8         arrPartOfURL = @[ 9                          @"chronograph",10                          @"color",11                          @"modular",12                          @"utility",13                          @"mickey_mouse",14                          @"simple",15                          @"motion",16                          @"solar",17                          @"astronomy",18                          @"timer",19                          @"alarm",20                          @"world_clock"21                          ];22     }23     24     NSUInteger randomVal = (arc4random() % 12); //0-11的隨機數25     NSString *imageURLStr = [NSString stringWithFormat:@"http://images.apple.com/v/watch/e/timekeeping/images/%@_large.jpg", arrPartOfURL[randomVal]];26     return [NSURL URLWithString:imageURLStr];27 }28 29 @end 

1 #import <UIKit/UIKit.h>2 3 @interface FirstSampleViewController : UIViewController4 @property (assign, nonatomic) CGSize rescaleImageSize;5 6 @property (strong, nonatomic) IBOutlet UIImageView *imgV;7 @property (strong, nonatomic) IBOutlet UIButton *btnLoadImage;8 9 @end 

  1 #import "FirstSampleViewController.h"  2 #import "UIImage+RescaleImage.h"  3 #import "Common.h"  4   5 @interface FirstSampleViewController ()  6 - (void)layoutUI;  7 - (void)updateImage:(NSData *)imageData;  8 @end  9  10 @implementation FirstSampleViewController 11  12 - (void)viewDidLoad { 13     [super viewDidLoad]; 14      15     [self layoutUI]; 16 } 17  18 - (void)didReceiveMemoryWarning { 19     [super didReceiveMemoryWarning]; 20     // Dispose of any resources that can be recreated. 21 } 22  23 - (void)dealloc { 24     _imgV.image = nil; 25 } 26  27 - (void)layoutUI { 28     self.view.backgroundColor = [UIColor colorWithWhite:0.957 alpha:1.000]; 29      30     CGFloat width = [[UIScreen mainScreen] bounds].size.width; //bounds 返回整個屏幕大??；applicationFrame 返回去除狀態欄后的屏幕大小 31     CGFloat height = width * 243.0 / 221.0; 32     const CGFloat percentVal = 3.0 / 4.0; //以屏幕寬度的3/4比例顯示 33     _rescaleImageSize = CGSizeMake(width * percentVal, height * percentVal); 34      35     //NSString *path = [[NSBundle mainBundle] pathForResource:@"PictureNo@2x" ofType:@"png"]; 36     //_imgV.image = [UIImage imageWithContentsOfFile:path]; 37      38     _btnLoadImage.tintColor = [UIColor darkGrayColor]; 39     _btnLoadImage.layer.masksToBounds = YES; 40     _btnLoadImage.layer.cornerRadius = 10.0; 41     _btnLoadImage.layer.borderColor = [UIColor grayColor].CGColor; 42     _btnLoadImage.layer.borderWidth = 1.0; 43 } 44  45 - (void)updateImage:(NSData *)imageData { 46     UIImage *img = [UIImage imageWithData:imageData]; 47     _imgV.image = [img rescaleImageToSize:_rescaleImageSize]; 48 } 49  50 - (IBAction)loadImage:(id)sender { 51     /* 52      GCD（Grand Central Dispatch）：中央調度 53      相比 NSThread 和 NSOperation 來說，他的顯著優點是：對于多核運算更加有效 54      1、GCD 的一個重要概念是隊列，他的核心理念：將多個任務添加到 dispatch queue（調度隊列）中，系統會為我們管理這些 dispath queue，為我們在多個線程上分配并執行任務，我們不需要直接啟動和管理后臺線程。 55      2、系統提供了許多預定義的 dispatch queue，包括可以保證始終在主線程上執行工作的 dispatch queue。也可以創建自己的dispatch queue，而且可以創建任意多個。GCD的 dispatch queue 嚴格遵循 FIFO（先進先出）原則，添加到 dispatch queue 的任務將始終按照加入 dispatch queue 的順序啟動。 56      3、dispatch queue按先進先出的順序，串行或并發地執行任務 57      1> serial dispatch queue（串行調度隊列）：一次只能執行一個任務，當前任務完成后才開始出列并啟動下一個任務 58      2> concurrent dispatch queue（并發調度隊列）：則盡可能多地啟動任務并發執行 59       60      同步和異步決定了要不要開啟新的線程 61      同步：在當前線程中執行任務，不具備開啟新線程的能力（如果當前線程是主線程的話，會造成線程阻塞，一般比較少用） 62      異步：在新的線程中執行任務，具備開啟新線程的能力 63       64      串行和并發決定了任務的執行方式 65      串行：一個任務執行完畢后，再執行下一個任務 66      并發：多個任務并發（同時）執行 67      */ 68      69     /* 70      系統給每個應用提供了四個全局并發隊列，整個應用內全局共享，他們的區別是通過「全局并發隊列優先級」；優先級越高，隊列越先被列入執行計劃中 71      #define DISPATCH_QUEUE_PRIORITY_HIGH 2 72      #define DISPATCH_QUEUE_PRIORITY_DEFAULT 0 73      #define DISPATCH_QUEUE_PRIORITY_LOW (-2) 74      #define DISPATCH_QUEUE_PRIORITY_BACKGROUND INT16_MIN 75      */ 76      77     //全局并發隊列 78     dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); 79      80     //自定義串行隊列；第二個參數為 NULL 或 DISPATCH_QUEUE_SERIAL 表示串行隊列，而為 DISPATCH_QUEUE_CONCURRENT 表示并發隊列，但一般用 dispatch_get_global_queue 方法獲取并發隊列 81     //dispatch_queue_t customSerialQueue = dispatch_queue_create("Custom Queue", NULL); 82      83     //主隊列；屬于串行隊列 84     dispatch_queue_t mainQueue = dispatch_get_main_queue(); 85      86      87     //方法一：自定義串行隊列同步：不會開啟新線程、串行執行任務 88 //    dispatch_sync(customSerialQueue, ^{ 89 //        NSLog(@"自定義串行隊列同步，線程：%@", [NSThread currentThread]); //所在的線程，這里就是在主線程 90 //        NSURL *url = [Common randomImageURL]; 91 //        NSData *data = [NSData dataWithContentsOfURL:url]; 92 //         93 //        dispatch_async(mainQueue, ^{ //主隊列異步（同步也一樣）：不會開啟新線程、串行執行任務 94 //            NSLog(@"主隊列異步（同步也一樣），線程：%@", [NSThread currentThread]); //主隊列所對應的主線程 95 //            [self updateImage:data]; 96 //        }); 97 //    }); 98      99     //方法二：自定義串行隊列異步：開啟新線程、串行執行任務100 //    dispatch_async(customSerialQueue, ^{101 //        NSLog(@"自定義串行隊列異步，線程：%@", [NSThread currentThread]); //開啟的新線程102 //        NSURL *url = [Common randomImageURL];103 //        NSData *data = [NSData dataWithContentsOfURL:url];104 //        105 //        dispatch_async(mainQueue, ^{ //主隊列異步（同步也一樣）：不會開啟新線程、串行執行任務106 //            NSLog(@"主隊列異步（同步也一樣），線程：%@", [NSThread currentThread]); //主隊列所對應的主線程107 //            [self updateImage:data];108 //        });109 //    });110     111     112     //方法三：全局并發隊列同步：不會開啟新線程、串行執行任務113 //    dispatch_sync(globalQueue, ^{114 //        NSLog(@"全局并發隊列同步，線程：%@", [NSThread currentThread]); //所在的線程，這里就是在主線程115 //        NSURL *url = [Common randomImageURL];116 //        NSData *data = [NSData dataWithContentsOfURL:url];117 //        118 //        dispatch_async(mainQueue, ^{ //主隊列異步（同步也一樣）：不會開啟新線程、串行執行任務119 //            NSLog(@"主隊列異步（同步也一樣），線程：%@", [NSThread currentThread]); //主隊列所對應的主線程120 //            [self updateImage:data];121 //        });122 //    });123     124     125     //方法四：全局并發隊列異步：開啟新線程、并發執行任務126     dispatch_async(globalQueue, ^{127         NSLog(@"全局并發隊列異步，線程：%@", [NSThread currentThread]); //開啟的新線程128         NSURL *url = [Common randomImageURL];129         NSData *data = [NSData dataWithContentsOfURL:url];130         131         dispatch_async(mainQueue, ^{ //主隊列異步（同步也一樣）：不會開啟新線程、串行執行任務132             NSLog(@"主隊列異步（同步也一樣），線程：%@", [NSThread currentThread]); //主隊列所對應的主線程133             [self updateImage:data];134         });135     });136 }137 138 @end 

 1 <?xml version="1.0" encoding="UTF-8" standalone="no"?> 2 <document type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="3.0" toolsVersion="7706" systemVersion="14E46" targetRuntime="iOS.CocoaTouch" propertyaccessControl="none" useAutolayout="YES" useTraitCollections="YES"> 3     <dependencies> 4         <deployment identifier="iOS"/> 5         <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="7703"/> 6     </dependencies> 7     <objects> 8         <placeholder placeholderIdentifier="IBFilesOwner" id="-1" userLabel="File's Owner" customClass="FirstSampleViewController"> 9             <connections>10                 <outlet property="btnLoadImage" destination="sLs-f1-Gzc" id="kX8-J0-v0V"/>11                 <outlet property="imgV" destination="4Qp-uk-KAb" id="RM3-Ha-glh"/>12                 <outlet property="view" destination="i5M-Pr-FkT" id="sfx-zR-JGt"/>13             </connections>14         </placeholder>15         <placeholder placeholderIdentifier="IBFirstResponder" id="-2" customClass="UIResponder"/>16         <view clearsContextBeforeDrawing="NO" contentMode="scaleToFill" id="i5M-Pr-FkT">17             <rect key="frame" x="0.0" y="0.0" width="600" height="600"/>18             <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>19             <subviews>20                 <imageView userInteractionEnabled="NO" contentMode="scaleToFill" horizontalHuggingPriority="251" verticalHuggingPriority="251" image="PictureNo.png" translatesAutoresizingMaskIntoConstraints="NO" id="4Qp-uk-KAb">21                     <rect key="frame" x="205" y="225" width="190" height="150"/>22                     <constraints>23                         <constraint firstAttribute="height" constant="150" id="S/>24                         <constraint firstAttribute="height" constant="150" id="VwM-i1-atB"/>25                         <constraint firstAttribute="width" constant="190" id="mUh-Bu-tUd"/>26                         <constraint firstAttribute="width" constant="190" id="mdJ-1c-QFa"/>27                         <constraint firstAttribute="width" constant="190" id="sVS-bU-Ty9"/>28                         <constraint firstAttribute="height" constant="150" id="uMG-oN-J56"/>29                         <constraint firstAttribute="height" constant="150" id="vws-Qw-UrB"/>30                     </constraints>31                     <variation key="default">32                         <mask key="constraints">33                             <exclude reference="SIp-Wd-idU"/>34                             <exclude reference="VwM-i1-atB"/>35                             <exclude reference="mUh-Bu-tUd"/>36                             <exclude reference="mdJ-1c-QFa"/>37                             <exclude reference="sVS-bU-Ty9"/>38                             <exclude reference="uMG-oN-J56"/>39                             <exclude reference="vws-Qw-UrB"/>40                         </mask>41                     </variation>42                 </imageView>43                 <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="sLs-f1-Gzc">44                     <rect key="frame" x="230" y="500" width="140" height="50"/>45                     <constraints>46                         <constraint firstAttribute="width" constant="140" id="1jv-9K-mdH"/>47                         <constraint firstAttribute="height" constant="50" id="Q2w-vR-9ac"/>48                     </constraints>49                     <state key="normal" title="加載網絡圖片">50                         <color key="titleShadowColor" white="0.5" alpha="1" colorSpace="calibratedWhite"/>51                     </state>52                     <connections>53                         <action selector="loadImage:" destination="-1" eventType="touchUpInside" id="fdy-Ln-5oS"/>54                     </connections>55                 </button>56             </subviews>57             <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>58             <constraints>59                 <constraint firstItem="4Qp-uk-KAb" firstAttribute="leading" secondItem="i5M-Pr-FkT" secondAttribute="leading" constant="205" id="2a2-mS-WFa"/>60                 <constraint firstItem="sLs-f1-Gzc" firstAttribute="top" secondItem="i5M-Pr-FkT" secondAttribute="top" id="ES4-wl-RBz"/>61                 <constraint firstItem="4Qp-uk-KAb" firstAttribute="centerY" secondItem="i5M-Pr-FkT" secondAttribute="centerY" id="MUJ-WA-sUf"/>62                 <constraint firstItem="4Qp-uk-KAb" firstAttribute="centerX" secondItem="sLs-f1-Gzc" secondAttribute="centerX" id="Q8a-1k-DzJ"/>63                 <constraint firstAttribute="bottom" secondItem="4Qp-uk-KAb" secondAttribute="bottom" constant="71" id="V0a-9y-Dwa"/>64                 <constraint firstAttribute="bottom" secondItem="sLs-f1-Gzc" secondAttribute="bottom" constant="50" id="VMG-CV-eeq"/>65                 <constraint firstItem="4Qp-uk-KAb" firstAttribute="top" secondItem="i5M-Pr-FkT" secondAttribute="top" constant="-71" id="gqW-Wq-4Zv"/>66                 <constraint firstItem="sLs-f1-Gzc" firstAttribute="centerX" secondItem="i5M-Pr-FkT" secondAttribute="centerX" id="kNf-6d-EJ8"/>67             </constraints>68             <variation key="default">69                 <mask key="constraints">70                     <exclude reference="2a2-mS-WFa"/>71                     <exclude reference="V0a-9y-Dwa"/>72                     <exclude reference="gqW-Wq-4Zv"/>73                     <exclude reference="ES4-wl-RBz"/>74                 </mask>75             </variation>76         </view>77     </objects>78     <resources>79         <image name="PictureNo.png" width="190" height="150"/>80     </resources>81 </document> 

1 #import <UIKit/UIKit.h>2 3 @interface SecondSampleViewController : UIViewController4 @property (assign, nonatomic) CGSize rescaleImageSize;5 @property (strong, nonatomic) NSMutableArray *mArrImageView;6 7 @property (strong, nonatomic) IBOutlet UIButton *btnLoadImage;8 9 @end 

  1 #import "SecondSampleViewController.h"  2 #import "UIImage+RescaleImage.h"  3 #import "Common.h"  4   5 #define kRowCount 4  6 #define kColumnCount 3  7 #define kCellSpacing 10.0  8   9 @interface SecondSampleViewController () 10 - (void)layoutUI; 11 - (void)updateImage:(NSData *)imageData withImageIndex:(NSInteger)imageIndex; 12 -(NSData *)requestData:(NSInteger)imageIndex; 13 - (void)loadImageFromNetwork:(NSInteger)imageIndex; 14 - (void)loadImageByDispatchAsync; 15 - (void)loadImageByDispatchApply; 16 - (void)loadImageByDispatchGroupAsync; 17 - (void)additionalInfo; 18 @end 19  20 @implementation SecondSampleViewController 21  22 - (void)viewDidLoad { 23     [super viewDidLoad]; 24      25     [self layoutUI]; 26 } 27  28 - (void)didReceiveMemoryWarning { 29     [super didReceiveMemoryWarning]; 30     // Dispose of any resources that can be recreated. 31 } 32  33 - (void)dealloc { 34     _mArrImageView = nil; 35 } 36  37 - (void)layoutUI { 38     self.view.backgroundColor = [UIColor colorWithWhite:0.957 alpha:1.000]; 39      40     CGFloat width = ([[UIScreen mainScreen] bounds].size.width - ((kColumnCount + 1) * kCellSpacing)) / kColumnCount; 41     _rescaleImageSize = CGSizeMake(width, width); 42      43     CGFloat heightOfStatusAndNav = 20.0 + 44.0; 44     NSString *path = [[NSBundle mainBundle] pathForResource:@"PictureNo@2x" ofType:@"png"]; 45     UIImage *img = [UIImage imageWithContentsOfFile:path]; 46     _mArrImageView = [NSMutableArray arrayWithCapacity:kRowCount * kColumnCount]; 47     //初始化多個圖片視圖 48     for (NSUInteger i=0; i<kRowCount; i++) { 49         for (NSUInteger j=0; j<kColumnCount; j++) { 50             UIImageView *imgV = [[UIImageView alloc] initWithFrame: 51                                  CGRectMake(_rescaleImageSize.width * j + kCellSpacing * (j+1), 52                                             _rescaleImageSize.height * i + kCellSpacing * (i+1) + heightOfStatusAndNav, 53                                             _rescaleImageSize.width, 54                                             _rescaleImageSize.height)]; 55             imgV.image = img; 56             [self.view addSubview:imgV]; 57             [_mArrImageView addObject:imgV]; 58         } 59     } 60      61     _btnLoadImage.tintColor = [UIColor darkGrayColor]; 62     _btnLoadImage.layer.masksToBounds = YES; 63     _btnLoadImage.layer.cornerRadius = 10.0; 64     _btnLoadImage.layer.borderColor = [UIColor grayColor].CGColor; 65     _btnLoadImage.layer.borderWidth = 1.0; 66 } 67  68 - (void)updateImage:(NSData *)imageData withImageIndex:(NSInteger)imageIndex { 69     UIImage *img = [UIImage imageWithData:imageData]; 70     UIImageView *imgVCurrent = _mArrImageView[imageIndex]; 71     imgVCurrent.image = [img rescaleImageToSize:_rescaleImageSize]; 72 } 73  74 -(NSData *)requestData:(NSInteger)imageIndex { 75     //對于多線程操作，建議把線程操作放到 @autoreleasepool 中 76     @autoreleasepool { 77         NSURL *url = [Common randomImageURL]; 78         NSData *data = [NSData dataWithContentsOfURL:url]; 79         return data; 80     } 81 } 82  83 - (void)loadImageFromNetwork:(NSInteger)imageIndex { 84     NSData *data = [self requestData:imageIndex]; 85      86     NSLog(@"Current thread:%@, imageIndex:%ld", [NSThread currentThread], (long)imageIndex); //dispatch_async、dispatch_apply、dispatch_group_async 的全局并發隊列，會開啟多個新線程去執行多個任務；按系統管理，也可能存在一個線程執行兩個任務的情況 87      88     dispatch_async(dispatch_get_main_queue(), ^{ //主隊列異步（同步也一樣）：不會開啟新線程、串行執行任務 89         NSLog(@"主隊列異步（同步也一樣），線程：%@", [NSThread currentThread]); //主隊列所對應的主線程 90         [self updateImage:data withImageIndex:imageIndex]; 91     }); 92 } 93  94 #pragma mark - 三種方法實現多線程并發執行多個任務，并且優先加載最后一張圖片 95 - (void)loadImageByDispatchAsync { 96     dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); //全局并發隊列 97      98     dispatch_async(globalQueue, ^{ 99         NSInteger len = kRowCount * kColumnCount - 1;100         101         NSLog(@"全局并發隊列異步，線程：%@", [NSThread currentThread]); //開啟的新線程102         [self loadImageFromNetwork:len]; //優先加載最后一張圖片103         104         for (NSUInteger i=0; i<len; i++) {105             dispatch_async(globalQueue, ^{106                 [self loadImageFromNetwork:i];107             });108         }109     });110 }111 112 - (void)loadImageByDispatchApply {113     dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); //全局并發隊列114     115     //使用 dispatch_async，全局并發隊列異步：開啟新線程、并發執行任務；此時會并發無序地逐個圖片加載并顯示出來116     //PS：如果使用 dispatch_sync，全局并發隊列同步：不會開啟新線程、串行執行任務；此時會等到全部圖片加載完才全部顯示出來117     dispatch_async(globalQueue, ^{118         size_t len = kRowCount * kColumnCount - 1;119         120         NSLog(@"全局并發隊列異步，線程：%@", [NSThread currentThread]); //開啟的新線程121         [self loadImageFromNetwork:len]; //優先加載最后一張圖片122         123         //使用 dispatch_apply 或 dispatch_apply_f 來循環迭代執行任務；前提是迭代的任務相互獨立，而且任務執行順序是無關緊要的；124         //他每次循環迭代會將指定的任務提交到 queue，queue 會開啟多個新線程（線程會盡量復用，線程更少，系統多線程之間切換調度更快）去執行多個任務，執行順序是不會像 for 循環那樣有序執行；125         //但是他像 for 循環一樣會在所有任務循環迭代執行完后才返回，會阻塞當前線程，所以只用于并發隊列。如果用于串行隊列，會造成死鎖，無法正常執行126         dispatch_apply(len, globalQueue, ^(size_t i) {127             [self loadImageFromNetwork:i];128         });129     });130 }131 132 - (void)loadImageByDispatchGroupAsync {133     dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); //全局并發隊列134     135     //使用 dispatch_async，全局并發隊列異步：開啟新線程、并發執行任務；此時會并發無序地逐個圖片加載并顯示出來136     //PS：如果使用 dispatch_sync，全局并發隊列同步：不會開啟新線程、串行執行任務；此時會等到全部圖片加載完才全部顯示出來137     dispatch_async(globalQueue, ^{138         NSInteger len = kRowCount * kColumnCount - 1;139         140         NSLog(@"全局并發隊列異步，線程：%@", [NSThread currentThread]); //開啟的新線程141         [self loadImageFromNetwork:len]; //優先加載最后一張圖片142         143         dispatch_group_t group = dispatch_group_create(); //自定義組144         for (NSUInteger i=0; i<len; i++) {145              //把一系列任務提交到隊列中，并統一關聯到自定義組中；這樣并發全部執行完畢后，能通過 dispatch_group_notify 進行后續處理146             dispatch_group_async(group, globalQueue, ^{147                 [self loadImageFromNetwork:i];148             });149         }150         151         //自定義組通知；會根據隊列類型決定是否開啟新線程；如果是并發隊列就會開啟新線程（實際上是：復用自定義組執行最后一個任務的對應線程），否則是串行隊列就不會152         dispatch_group_notify(group, dispatch_get_main_queue(), ^{153             NSLog(@"自定義組通知，線程：%@", [NSThread currentThread]);154             NSLog(@"全部的 dispatch_group_async 任務執行完畢后，做一些事情，只執行一次");155         });156     });157 }158 159 - (void)additionalInfo {160     //dispatch_suspend(queue); //掛起隊列方法；當前正在執行的任務不會停下來，只是不再繼續執行未啟動的任務161     //dispatch_resume(queue); //恢復隊列方法；確保他跟 dispatch_suspend 成對調用162     163     //單次執行任務方法；方法是線程安全的164     static dispatch_once_t onceToken;165     dispatch_once(&onceToken, ^{166         NSLog(@"dispatch_once：單次執行任務；只會執行一次，重復調用方法也不會重復執行（可用于應用程序中初始化全局數據的情況，例如：單例模式）");167     });168     169     //類似 - (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay 的延時執行方法170     dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{171         NSLog(@"dispatch_after：延時執行任務，這里2.0秒后做一些事情");172     });173 }174 175 - (IBAction)loadImage:(id)sender {176     //三種方法實現多線程并發執行多個任務，并且優先加載最后一張圖片177     //方法一：dispatch_async178     //[self loadImageByDispatchAsync];179     180     //方法二：dispatch_apply181     //[self loadImageByDispatchApply];182     183     //方法三：dispatch_group_async184     [self loadImageByDispatchGroupAsync];185     186     187     //附加信息188     [self additionalInfo];189 }190 191 @end 

 1 <?xml version="1.0" encoding="UTF-8" standalone="no"?> 2 <document type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="3.0" toolsVersion="7706" systemVersion="14E46" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES"> 3     <dependencies> 4         <deployment identifier="iOS"/> 5         <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="7703"/> 6     </dependencies> 7     <objects> 8         <placeholder placeholderIdentifier="IBFilesOwner" id="-1" userLabel="File's Owner" customClass="SecondSampleViewController"> 9             <connections>10                 <outlet property="btnLoadImage" destination="F5h-ZI-gGL" id="I40-e2-bAa"/>11                 <outlet property="view" destination="i5M-Pr-FkT" id="sfx-zR-JGt"/>12             </connections>13         </placeholder>14         <placeholder placeholderIdentifier="IBFirstResponder" id="-2" customClass="UIResponder"/>15         <view clearsContextBeforeDrawing="NO" contentMode="scaleToFill" id="i5M-Pr-FkT">16             <rect key="frame" x="0.0" y="0.0" width="600" height="600"/>17             <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>18             <subviews>19                 <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="F5h-ZI-gGL">20                     <rect key="frame" x="230" y="530" width="140" height="50"/>21                     <constraints>22                         <constraint firstAttribute="height" constant="50" id="HWd-Xc-Wk7"/>23                         <constraint firstAttribute="width" constant="140" id="vrH-qE-PNK"/>24                     </constraints>25                     <state key="normal" title="加載網絡圖片">26                         <color key="titleShadowColor" white="0.5" alpha="1" colorSpace="calibratedWhite"/>27                     </state>28                     <connections>29                         <action selector="loadImage:" destination="-1" eventType="touchUpInside" id="Hgw-q8-lHy"/>30                     </connections>31                 </button>32             </subviews>33             <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>34             <constraints>35                 <constraint firstAttribute="bottom" secondItem="F5h-ZI-gGL" secondAttribute="bottom" constant="20" id="jPY-fY-9XJ"/>36                 <constraint firstAttribute="centerX" secondItem="F5h-ZI-gGL" secondAttribute="centerX" id="rH1-sV-pST"/>37             </constraints>38         </view>39     </objects>40 </document> 

1 #import <UIKit/UIKit.h>2 3 @interface AppDelegate : UIResponder <UIApplicationDelegate>4 5 @property (strong, nonatomic) UIWindow *window;6 @property (strong, nonatomic) UINavigationController *navigationController;7 8 @end 

 1 #import "AppDelegate.h" 2 #import "ViewController.h" 3  4 @interface AppDelegate () 5  6 @end 7  8 @implementation AppDelegate 9 10 11 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {12     _window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];13     ViewController *viewController = [[ViewController alloc] initWithSampleNameArray:@[@"請求單張網絡圖片（解決線程阻塞）", @"請求多張網絡圖片（多個線程并發）"]];14     _navigationController = [[UINavigationController alloc] initWithRootViewController:viewController];15     _window.rootViewController = _navigationController;16     //[_window addSubview:_navigationController.view]; //當_window.rootViewController關聯時，這一句可有可無17     [_window makeKeyAndVisible];18     return YES;19 }20 21 - (void)applicationWillResignActive:(UIApplication *)application {22 }23 24 - (void)applicationDidEnterBackground:(UIApplication *)application {25 }26 27 - (void)applicationWillEnterForeground:(UIApplication *)application {28 }29 30 - (void)applicationDidBecomeActive:(UIApplication *)application {31 }32 33 - (void)applicationWillTerminate:(UIApplication *)application {34 }35 36 @end 

 1 2015-08-30 17:19:44.168 GCDDemo[4776:70114] 全局并發隊列異步，線程：<NSThread: 0x7f9511c7a920>{number = 4, name = (null)} 2 2015-08-30 17:19:44.168 GCDDemo[4776:70265] dispatch_once：單次執行任務；只會執行一次，重復調用方法也不會重復執行（可用于應用程序中初始化全局數據的情況，例如：單例模式） 3 2015-08-30 17:19:44.229 GCDDemo[4776:70265] Current thread:<NSThread: 0x7f9511c7a920>{number = 4, name = (null)}, imageIndex:11 4 2015-08-30 17:19:44.230 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main} 5 2015-08-30 17:19:44.283 GCDDemo[4776:70265] Current thread:<NSThread: 0x7f9511c7a920>{number = 4, name = (null)}, imageIndex:0 6 2015-08-30 17:19:44.283 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main} 7 2015-08-30 17:19:44.301 GCDDemo[4776:70248] Current thread:<NSThread: 0x7f9511f2b3f0>{number = 2, name = (null)}, imageIndex:1 8 2015-08-30 17:19:44.301 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main} 9 2015-08-30 17:19:44.516 GCDDemo[4776:70269] Current thread:<NSThread: 0x7f9511ef52f0>{number = 5, name = (null)}, imageIndex:210 2015-08-30 17:19:44.516 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}11 2015-08-30 17:19:44.887 GCDDemo[4776:70241] Current thread:<NSThread: 0x7f9511d94230>{number = 6, name = (null)}, imageIndex:612 2015-08-30 17:19:44.888 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}13 2015-08-30 17:19:44.999 GCDDemo[4776:70299] Current thread:<NSThread: 0x7f9511d93d40>{number = 7, name = (null)}, imageIndex:314 2015-08-30 17:19:44.999 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}15 2015-08-30 17:19:45.152 GCDDemo[4776:70301] Current thread:<NSThread: 0x7f9511d78f90>{number = 8, name = (null)}, imageIndex:516 2015-08-30 17:19:45.152 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}17 2015-08-30 17:19:45.190 GCDDemo[4776:70300] Current thread:<NSThread: 0x7f9511ef0340>{number = 9, name = (null)}, imageIndex:418 2015-08-30 17:19:45.190 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}19 2015-08-30 17:19:45.240 GCDDemo[4776:70304] Current thread:<NSThread: 0x7f9511d8e9d0>{number = 10, name = (null)}, imageIndex:820 2015-08-30 17:19:45.240 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}21 2015-08-30 17:19:45.314 GCDDemo[4776:70305] Current thread:<NSThread: 0x7f9511ecd030>{number = 11, name = (null)}, imageIndex:1022 2015-08-30 17:19:45.314 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}23 2015-08-30 17:19:45.443 GCDDemo[4776:70302] Current thread:<NSThread: 0x7f9511d8fc50>{number = 12, name = (null)}, imageIndex:724 2015-08-30 17:19:45.443 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}25 2015-08-30 17:19:45.615 GCDDemo[4776:70303] Current thread:<NSThread: 0x7f9511d91740>{number = 13, name = (null)}, imageIndex:926 2015-08-30 17:19:45.615 GCDDemo[4776:70114] 主隊列異步（同步也一樣），線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}27 2015-08-30 17:19:45.620 GCDDemo[4776:70114] 自定義組通知，線程：<NSThread: 0x7f9511d0a9a0>{number = 1, name = main}28 2015-08-30 17:19:45.620 GCDDemo[4776:70114] 全部的 dispatch_group_async 任務執行完畢后，做一些事情，只執行一次29 2015-08-30 17:19:46.360 GCDDemo[4776:70114] dispatch_after：延時執行任務，這里2.0秒后做一些事情 

 1 2015-08-30 17:15:08.490 GCDDemo[4668:66939] 全局并發隊列異步，線程：<NSThread: 0x7fc5be00c810>{number = 2, name = (null)} 2 2015-08-30 17:15:08.490 GCDDemo[4668:66894] dispatch_once：單次執行任務；只會執行一次，重復調用方法也不會重復執行（可用于應用程序中初始化全局數據的情況，例如：單例模式） 3 2015-08-30 17:15:08.862 GCDDemo[4668:66939] Current thread:<NSThread: 0x7fc5be00c810>{number = 2, name = (null)}, imageIndex:11 4 2015-08-30 17:15:08.862 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main} 5 2015-08-30 17:15:09.062 GCDDemo[4668:66981] Current thread:<NSThread: 0x7fc5be05ac90>{number = 4, name = (null)}, imageIndex:3 6 2015-08-30 17:15:09.062 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main} 7 2015-08-30 17:15:09.066 GCDDemo[4668:66939] Current thread:<NSThread: 0x7fc5be00c810>{number = 2, name = (null)}, imageIndex:0 8 2015-08-30 17:15:09.067 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main} 9 2015-08-30 17:15:09.323 GCDDemo[4668:66941] Current thread:<NSThread: 0x7fc5bbf60040>{number = 5, name = (null)}, imageIndex:210 2015-08-30 17:15:09.323 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main}11 2015-08-30 17:15:09.323 GCDDemo[4668:66940] Current thread:<NSThread: 0x7fc5be05bf50>{number = 6, name = (null)}, imageIndex:112 2015-08-30 17:15:09.324 GCDDemo[4668:66942] Current thread:<NSThread: 0x7fc5bbd05bf0>{number = 7, name = (null)}, imageIndex:413 2015-08-30 17:15:09.327 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main}14 2015-08-30 17:15:09.330 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main}15 2015-08-30 17:15:09.486 GCDDemo[4668:66991] Current thread:<NSThread: 0x7fc5bbd1f880>{number = 8, name = (null)}, imageIndex:716 2015-08-30 17:15:09.486 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main}17 2015-08-30 17:15:10.156 GCDDemo[4668:66988] Current thread:<NSThread: 0x7fc5be05ae70>{number = 9, name = (null)}, imageIndex:518 2015-08-30 17:15:10.156 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main}19 2015-08-30 17:15:10.208 GCDDemo[4668:66990] Current thread:<NSThread: 0x7fc5bbd26b00>{number = 10, name = (null)}, imageIndex:620 2015-08-30 17:15:10.209 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main}21 2015-08-30 17:15:10.239 GCDDemo[4668:66992] Current thread:<NSThread: 0x7fc5bbe9ff30>{number = 11, name = (null)}, imageIndex:822 2015-08-30 17:15:10.239 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main}23 2015-08-30 17:15:10.491 GCDDemo[4668:66894] dispatch_after：延時執行任務，這里2.0秒后做一些事情24 2015-08-30 17:15:10.838 GCDDemo[4668:66993] Current thread:<NSThread: 0x7fc5bbea3940>{number = 12, name = (null)}, imageIndex:925 2015-08-30 17:15:10.838 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main}26 2015-08-30 17:15:11.489 GCDDemo[4668:66989] Current thread:<NSThread: 0x7fc5bbea4dd0>{number = 13, name = (null)}, imageIndex:1027 2015-08-30 17:15:11.490 GCDDemo[4668:66894] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fc5bbe280d0>{number = 1, name = main} 

 1 2015-08-30 17:15:50.873 GCDDemo[4694:67547] 全局并發隊列異步，線程：<NSThread: 0x7fe57149bb60>{number = 2, name = (null)} 2 2015-08-30 17:15:50.873 GCDDemo[4694:67503] dispatch_once：單次執行任務；只會執行一次，重復調用方法也不會重復執行（可用于應用程序中初始化全局數據的情況，例如：單例模式） 3 2015-08-30 17:15:50.973 GCDDemo[4694:67547] Current thread:<NSThread: 0x7fe57149bb60>{number = 2, name = (null)}, imageIndex:11 4 2015-08-30 17:15:50.974 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main} 5 2015-08-30 17:15:51.018 GCDDemo[4694:67546] Current thread:<NSThread: 0x7fe5714f8490>{number = 4, name = (null)}, imageIndex:1 6 2015-08-30 17:15:51.018 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main} 7 2015-08-30 17:15:51.078 GCDDemo[4694:67546] Current thread:<NSThread: 0x7fe5714f8490>{number = 4, name = (null)}, imageIndex:4 8 2015-08-30 17:15:51.078 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main} 9 2015-08-30 17:15:51.087 GCDDemo[4694:67562] Current thread:<NSThread: 0x7fe5717bd740>{number = 5, name = (null)}, imageIndex:210 2015-08-30 17:15:51.087 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}11 2015-08-30 17:15:51.200 GCDDemo[4694:67547] Current thread:<NSThread: 0x7fe57149bb60>{number = 2, name = (null)}, imageIndex:012 2015-08-30 17:15:51.200 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}13 2015-08-30 17:15:51.271 GCDDemo[4694:67562] Current thread:<NSThread: 0x7fe5717bd740>{number = 5, name = (null)}, imageIndex:614 2015-08-30 17:15:51.271 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}15 2015-08-30 17:15:51.628 GCDDemo[4694:67549] Current thread:<NSThread: 0x7fe57152d910>{number = 6, name = (null)}, imageIndex:316 2015-08-30 17:15:51.628 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}17 2015-08-30 17:15:51.701 GCDDemo[4694:67546] Current thread:<NSThread: 0x7fe5714f8490>{number = 4, name = (null)}, imageIndex:518 2015-08-30 17:15:51.701 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}19 2015-08-30 17:15:51.800 GCDDemo[4694:67547] Current thread:<NSThread: 0x7fe57149bb60>{number = 2, name = (null)}, imageIndex:720 2015-08-30 17:15:51.800 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}21 2015-08-30 17:15:52.063 GCDDemo[4694:67549] Current thread:<NSThread: 0x7fe57152d910>{number = 6, name = (null)}, imageIndex:922 2015-08-30 17:15:52.064 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}23 2015-08-30 17:15:52.109 GCDDemo[4694:67562] Current thread:<NSThread: 0x7fe5717bd740>{number = 5, name = (null)}, imageIndex:824 2015-08-30 17:15:52.110 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}25 2015-08-30 17:15:52.295 GCDDemo[4694:67546] Current thread:<NSThread: 0x7fe5714f8490>{number = 4, name = (null)}, imageIndex:1026 2015-08-30 17:15:52.295 GCDDemo[4694:67503] 主隊列異步（同步也一樣），線程：<NSThread: 0x7fe571428b10>{number = 1, name = main}27 2015-08-30 17:15:52.874 GCDDemo[4694:67503] dispatch_after：延時執行任務，這里2.0秒后做一些事情