I have a UITableView, when a cell is selected, I make a service call to asynchronously download a PDF file from a web service. It works great, until you select multiple cells directly after one-another (individually), then things start going south..
Here's some (stripped down) code to clarify:
Inside MasterViewController.m:
- (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.
}
}
Inside ReportDownloader.m:
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]);
}
The above code works fine for a single report. And on a fast line, it works fine for 3-4 reports, but try to do more than that and the Expected length starts mismatching the Actual length. And I can't understand whyyyyy....
See the output generated by the code above: (Notice that only the report for indexPath 1.1 was downloaded correctly)
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
The data corruption is confirmed when trying to open the PDF documents, which fail for all file's who's data size didn't match the expectedContentLength.
I am completely baffled by this behaviour, I'm hoping that I'm making an obvious n00b mistake and that someone here spots it.
The main reason WHY I made the ReportDownloader class was to avoid problems like this one.
Thanks in advance to whoever takes the time to scan my code!
