前言

我们目前有写网络请求是需要依赖前面一个或多个网络请求的回掉之后才能执行后面的操作。

比如我们的一个APP首页由多个网络请求的回掉结果之后才有刷新整个页面，这里就需要将所有模块的网络请求回掉成功之后在执行relodData操作。为了提高网络请求效率和满足业务需求，多线程并发网络请求，等待所有网络请求回掉成功之后在执行Controller 的刷新操作，就成为了一种需求。

代码的下载地址demo;

代码

这里提供了两种实现方式，一种是队列组group，一种是信号量semaphore。
详细见代码即可。
代码部分github上也上传了一份

#import "NetWorkingViewController.h"

@interface NetWorkingViewController ()

@property (nonatomic,strong) NSArray *picsArr;
@property (nonatomic,strong) UIImageView *imgV1;
@property (nonatomic,strong) UIImageView *imgV2;
@property (nonatomic,strong) UIImageView *imgV3;

@end

@implementation NetWorkingViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.picsArr = @[@"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1557058607482&di=e1658859cebd03ae2a017d1cf42965f7&imgtype=0&src=http%3A%2F%2Fimg.zhiribao.com%2Fupload%2Fimages%2F201607%2F6%2F6b0152a5b29f309f3f92f52adc6cd017eae73133.jpg",
                     @"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1557058607482&di=a1ea9132e7354e67b3c62eaacce4cacb&imgtype=0&src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F20182%2F21%2F2018221142159_MZ33z.jpeg",
                     @"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1557058607481&di=e5d2886ce2501a2ec7d66d01455e14c3&imgtype=0&src=http%3A%2F%2Fimg5.duitang.com%2Fuploads%2Fitem%2F201305%2F25%2F20130525153450_nHVaH.thumb.700_0.jpeg"];
    [self configUI];
}

- (void)configUI{
    
    CGFloat imgWidth = self.view.bounds.size.width * 0.3333333;
    
    self.imgV1 = [[UIImageView alloc] initWithFrame:CGRectMake(0, 80, imgWidth, 100)];
    self.imgV2 = [[UIImageView alloc] initWithFrame:CGRectMake(imgWidth, 80, imgWidth, 100)];
    self.imgV3 = [[UIImageView alloc] initWithFrame:CGRectMake(imgWidth * 2, 80, imgWidth, 100)];

    [self.view addSubview:self.imgV1];
    [self.view addSubview:self.imgV2];
    [self.view addSubview:self.imgV3];
    
    CGFloat btnWidth = self.view.bounds.size.width;
    UIButton *netWorkingBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    netWorkingBtn.frame  = CGRectMake(0, 200, btnWidth, 60);
    [netWorkingBtn addTarget:self action:@selector(netWorkingBegin:) forControlEvents:UIControlEventTouchUpInside];
    [netWorkingBtn setTitle:@"开始下载" forState:UIControlStateNormal];
    [netWorkingBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [self.view addSubview:netWorkingBtn];

}


- (void)netWorkingBegin:(UIButton *)sender{
    
//    [self groupNetWorkingWithSender:sender];
    
    [self semaphoreNetWorkingWithSender:sender];
}


- (void)semaphoreNetWorkingWithSender:(UIButton *)sender{
    
    [sender setTitle:@"正在下载" forState:UIControlStateNormal];
    [sender setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
    
    self.imgV1.image = nil;
    self.imgV2.image = nil;
    self.imgV3.image = nil;
    
    NSArray <UIImageView *> *imgVs = @[self.imgV1,self.imgV2,self.imgV3];
    
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    for ( int i = 0; i < self.picsArr.count; i++) {
        NSLog(@"第%d张开始下载",i);
        [self netWorkingDownloadPicWithUrlStr:self.picsArr[i] completionHandler:^(UIImage *img) {
            NSLog(@"第%d张下载完成",i);
            dispatch_async(dispatch_get_main_queue(), ^{
                imgVs[i].image = img;
            });
            dispatch_semaphore_signal(semaphore);
        }];
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    };
    
    NSLog(@"所有的图片下载完成");
    [sender setTitle:@"下载完成" forState:UIControlStateNormal];
    [sender setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    
}


/**
 采用GCD 并发组

 @param sender <#sender description#>
 */
- (void)groupNetWorkingWithSender:(UIButton *)sender{
    [sender setTitle:@"正在下载" forState:UIControlStateNormal];
    [sender setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
    
    self.imgV1.image = nil;
    self.imgV2.image = nil;
    self.imgV3.image = nil;
    
    NSArray <UIImageView *> *imgVs = @[self.imgV1,self.imgV2,self.imgV3];
    
    dispatch_group_t group =  dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    
    for ( int i = 0; i < self.picsArr.count; i++) {
        NSLog(@"第%d张开始下载",i);
        dispatch_group_enter(group);
        dispatch_async(queue, ^{
            [self netWorkingDownloadPicWithUrlStr:self.picsArr[i] completionHandler:^(UIImage *img) {
                NSLog(@"第%d张下载完成",i);
                dispatch_group_leave(group);
                dispatch_async(dispatch_get_main_queue(), ^{
                    imgVs[i].image = img;
                });
                
            }];
        });
    }
    
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"所有的图片下载完成");
        [sender setTitle:@"下载完成" forState:UIControlStateNormal];
        [sender setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    });
    
}



/**
 网络请求下载网络上的图片

 @param urlStr 图片地址
 @param completionHandler 下载完成后的回掉
 */
- (void)netWorkingDownloadPicWithUrlStr:(NSString *)urlStr completionHandler:(void(^)(UIImage *img))completionHandler {
    
    NSURL *url = [NSURL URLWithString:urlStr];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        
        if (!error && data) {
            
            UIImage *image = [UIImage imageWithData:data];
            !completionHandler ? :completionHandler(image);
            
        }else{
            
            !completionHandler ? :completionHandler(nil);
            
        }
        
    }];
    [dataTask resume];
    
}