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I have a UITableView, when a cell is selected, I make a service call to asynchronously download a PDF file from a web service. 它工作得很好，直到您一个接一个（单独）选择多个单元格，然后事情开始向南......

这里有一些（精简）代码来澄清：

在 MasterViewController.m 中：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    //To uniquely identify this field, I build a simple string using the indexPath.
    NSString *key = [[NSString alloc]initWithFormat:@"%d.%d",pIndex.section,pIndex.row];

    //Use a pre-populated NSDictionary to specify the file I want from the server.
    NSString *reportID = [reportDictionary valueForKey:key];

    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%@/RequestReportWithID",myConnectionObject.ServiceURL]];

    NSMutableDictionary *body = [[NSMutableDictionary alloc] initWithObjectsAndKeys:reportID, @"reportID", nil];

    NSData *requestData = [NSJSONSerialization dataWithJSONObject:dic options:0 error:nil];

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

    [request setHTTPMethod:@"POST"];
    [request setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
    [request setValue:[NSString stringWithFormat:@"%d", [requestData length]] forHTTPHeaderField:@"Content-Length"];
    [request setHTTPBody: requestData];

    //Create a new object as delegate to receive the data, also add the key to assist with identification.
    ReportDownloader *newReportDownloader = [[ReportDownloader alloc]initWithDelegate:self andKey:key];

    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:newReportDownloader];
    if (connection)
    {
        //Nothing to do here, request was made.
    }
}

在 ReportDownloader.m 中：

long long expectedReportSize;
NSString *key;
NSData *thisReport;

-(NSObject*)initWithDelegate:(NSObject*)pDelegate andKey:(NSString*)pKey
{
    myTypedDelegate = (MasterViewController*)pDelegate;
    Key = pKey;
    return self;
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    expectedReportSize = [response expectedContentLength];
    NSLog(@"Key:%@, Expected Size=%lld bytes",Key, [response expectedContentLength]);
    thisReport = [[NSMutableData alloc] init];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data 
{
    [thisReport appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection 
{
    //Here is where things go wrong...
    NSLog(@"Key:%@, Actual Size=%ld bytes",Key, (unsigned long)[thisReport length]);
}

上面的代码适用于单个报告。在快速线上，它适用于 3-4 份报告，但尝试做的不止于此，预期长度开始与实际长度不匹配。而且我不明白为什么yyyy....

查看上面代码生成的输出：（ 注意只有 indexPath 1.1 的报告被正确下载）

Key:1.0, Expected Size=304006 bytes
Key:1.3, Expected Size=124922 bytes
Key:1.0,   Actual Size=369494 bytes
Key:1.3,   Actual Size=380030 bytes
Key:1.2, Expected Size=179840 bytes
Key:1.4, Expected Size=377046 bytes
Key:1.2,   Actual Size=114376 bytes
Key:1.5, Expected Size=175633 bytes
Key:1.4,   Actual Size=180558 bytes
Key:1.5,   Actual Size=274549 bytes
Key:1.1, Expected Size=443135 bytes
Key:1.1,   Actual Size=443135 bytes

尝试打开 PDF 文档时确认数据损坏，对于所有文件的数据大小与预期内容长度不匹配的文件均失败。

我对这种行为完全感到困惑，我希望我犯了一个明显的 n00b 错误，并且这里有人发现了它。

我制作 ReportDownloader 类的主要原因是为了避免这样的问题。

提前感谢花时间扫描我的代码的人！

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1 回答 1

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好的，可以在此处找到此问题的解决方案： https ://stackoverflow.com/a/1938395/1014983 James Wald 的这个答案，虽然不是问题的公认答案，但完全解决了我使用多个同时异步 NSURLConnections 的所有问题。

如果您在实施方面需要一些帮助，请告诉我，但这很简单。

于 2013-04-11T08:32:23.553 回答