NSOperationQueue 实现串行请求

demo.m

//用了表示是否有异步请求正在执行
@property (assign, atomic) BOOL excuting;
@property (strong, nonatomic) NSArray *datasArray;
@property (strong, nonatomic) NSOperationQueue *operationQueue;

- (void)ViewDidLoad {
  [super viewDidLoad];
  self.excuting = NO;
  self.operationQueue = [[NSOperationQueue alloc] init];
  [self.operationQueue setMaxConcurrentOperationCount:1];
  NSInvocationOperation *previousOperation = nil;
  for(id data in datasArray) {
      NSInvocationOperation *operation = [[NSInvocationOperation alloc] 
                                                          initWithTarget:self
                                                                selector:@selector(uploadDataToServer:)
                                                                  object:data];
      if(previousOperation) {
         [operation addDependency:previousOperation]
      }
      [self.operationQueue addOperation:operation];
      previousOperation = operation;
  }
}

- (void)uploadDataToServer:(id)data {
   NSURL *url = [NSURL URLWithString:@"https://api/"];
   NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
   [request setHTTPMethod:@"POST"];
   [request setTimeoutInterval:60];
   [request setHTTPBody:data];
   NSURLSessionDataTask *dataTask = [[NSURLSession sharedSession]
                                       dataTaskWithRequest:request
                                       completionHandler:^(NSData * _Nullable data, 
                                                           NSURLResponse * _Nullable response,
                                                           NSError * _Nullable error) {
                                        if (error) {
                                           //该任务执行有错误，取消后续任务
                                           [self.operationQueue cancelAllOperations];
                                        }
                                        else {
                                           self.excuting = false;
                                        }
                                    }];
    //如果有其他任务正在执行，则阻塞当前任务
    while(self.excuting) {
      
    }
    
    //开始当前任务
    [dataTask resume];
    self.excuting = YES;
}