iOS网络串行队列

参考链接：https://blog.csdn.net/dingqk/article/details/77878322
https://juejin.im/post/5a9e57af6fb9a028df222555
https://www.cnblogs.com/yajunLi/p/6274282.html

#import "ViewController.h"
#import "AFNetworking.h"

@interface ViewController () {
    NSMutableArray *_dataSource;
}
@property (nonatomic, strong) NSURLSessionDownloadTask *downloadTask;

@end

@implementation ViewController

- (void)download {
NSArray *downloadArray =
[@"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10
.com%2F28ea2e5cf17173f84ef74064e95627cc3ba75fe627e71-hKNgS4_fw6
@"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_100
.com%2F5f362385b8ffedc49172da5b056b03a5b54e191830b59-FM6lGh_fw6
@"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_100
.com%2F20110524%2F2457331_092725729000_2.jpg",
@"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_100
.com%2Fwallpaper%2F2018-08-16%2F5b750e40cbed0.jpg"];        // 设置最大线程数
    
    
    // 创建一个队列
    NSOperationQueue *queue = [[NSOperationQueue alloc]init];
    
    // 设置最大线程数
    queue.maxConcurrentOperationCount = 1;
    
    for (NSInteger i = 0; i < downloadArray.count; i++) {
        //创建一个队列数组
        NSMutableArray *operaQueueArray = [NSMutableArray array];
        
        NSBlockOperation *blockOpera = [NSBlockOperation blockOperationWithBlock:^{
            dispatch_semaphore_t semaphore = dispatch_semaphore_create(0); //默认创建的信号为0
            //1.创建会话管理者
            AFHTTPSessionManager *manager =[AFHTTPSessionManager manager];
            NSURL *url = [NSURL URLWithString:downloadArray[I]];
            
            NSURLRequest *request = [NSURLRequest requestWithURL:url];
            NSURLSessionDownloadTask *download = [manager downloadTaskWithRequest:request progress:^(NSProgress * _Nonnull downloadProgress) {
                
                //监听下载进度
                //completedUnitCount 已经下载的数据大小
                //totalUnitCount     文件数据的中大小
                NSLog(@"%f",1.0 *downloadProgress.completedUnitCount / downloadProgress.totalUnitCount);
                
            } destination:^NSURL * _Nonnull(NSURL * _Nonnull targetPath, NSURLResponse * _Nonnull response) {
                NSString *fullPath = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:response.suggestedFilename];
                
                NSLog(@"targetPath:%@",targetPath);
                
                NSLog(@"fullPath:%@",fullPath);
                dispatch_semaphore_signal(semaphore); //这里请求成功信号量 +1 为1
                
                
                return [NSURL fileURLWithPath:fullPath];
                
            } completionHandler:^(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error) {
                NSLog(@"%@",filePath);
                dispatch_semaphore_signal(semaphore); //这里请求成功信号量 +1 为1

            }];
            
            //3.执行Task
            [download resume];
            dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); //走到这里如果信号量为0 则不再执行下面的代码 一直等待 信号量不是0 出现 才会执行下面代码,然后信号量为 - 1
        }];
        //将创建的任务添加到数组中
        [operaQueueArray addObject:blockOpera];
        
        
        //添加依赖关系
        for (int i = 0; i < operaQueueArray.count; i++) {
            if (i > 0) {
                [operaQueueArray[i] addDependency:operaQueueArray[i - 1]];
            }
        }
        
        [queue addOperations:operaQueueArray waitUntilFinished:NO];
        [queue addObserver:self forKeyPath:@"operationCount" options:0 context:nil];

    };
}

- (void)viewDidLoad {
    [super viewDidLoad];
    [self download];
    NSLog(@"====");
}

//监听网络请求
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
    
    if ([keyPath isEqualToString:@"operationCount"]) {
        NSOperationQueue *queue = (NSOperationQueue *)object;
        if (queue.operationCount == 0) {
            //主线程刷新界面
            dispatch_async(dispatch_get_main_queue(), ^{
                NSLog(@"%d===",__LINE__);
            });
        }
    }
}

@end

效果图：