NSURLConnection sendAsynchronousRequest:queue:completionHandler:连续发出多个请求？

Question

我一直在使用NSURLConnection's sendAsynchronousRequest:queue:completionHandler:很棒的方法.但是,我现在需要连续发出多个请求.

如何在使用这种伟大的异步方法的同时做到这一点？

Answer 1

根据您想要的行为,您可以通过多种方式执行此操作.

您可以一次发送一堆异步请求,跟踪已完成的请求数,并在完成所有操作后执行一些操作:

NSInteger outstandingRequests = [requestsArray count];
for (NSURLRequest *request in requestsArray) {
    [NSURLConnection sendAsynchronousRequest:request 
                                       queue:[NSOperationQueue mainQueue]
                           completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
        [self doSomethingWithData:data];
        outstandingRequests--;
        if (outstandingRequests == 0) {
            [self doSomethingElse];
        }
    }];
}

你可以把块连在一起:

NSMutableArray *dataArray = [NSMutableArray array];    
__block (^handler)(NSURLResponse *response, NSData *data, NSError *error);

NSInteger currentRequestIndex = 0;
handler = ^{
    [dataArray addObject:data];
    currentRequestIndex++;
    if (currentRequestIndex < [requestsArray count]) {
        [NSURLConnection sendAsynchronousRequest:[requestsArray objectAtIndex:currentRequestIndex] 
                                   queue:[NSOperationQueue mainQueue]
                       completionHandler:handler];
    } else {
        [self doSomethingElse];
    }
};
[NSURLConnection sendAsynchronousRequest:[requestsArray objectAtIndex:0] 
                                   queue:[NSOperationQueue mainQueue]
                       completionHandler:handler];

或者您可以在ansynchronous块中同步执行所有请求:

dispatch_queue_t callerQueue = dispatch_get_current_queue();
dispatch_queue_t downloadQueue = dispatch_queue_create("Lots of requests", NULL);
    dispatch_async(downloadQueue, ^{
        for (NSRURLRequest *request in requestsArray) {
            [dataArray addObject:[NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil]];
        }
        dispatch_async(callerQueue, ^{
            [self doSomethingWithDataArray:dataArray];
        });
    });
});

PS如果你使用其中任何一个,你应该添加一些错误检查.