iPhone - How to download big amount of files - iphone

Question

I need to download a number of files from the server. What is the best way to do it?
All documents are stored in NSMutableArray and for each documents there are two files - the document itself and its change log. So what I do is:
- (void)downloadDocuments:(int)docNumber
{
NSString *urlString;
NSURL *url;
for (int i=0; i<[items count]; i++) {
[progressBar setProgress:((float)i/[items count]) animated:YES];
urlString = [[items objectAtIndex:i] docUrl];
url = [[NSURL alloc] initWithString:[urlString stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding]];
[self downloadSingleDocument:url];
urlString = [[items objectAtIndex:i] changeLogUrl];
url = [[NSURL alloc] initWithString:[urlString stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding]];
[self downloadSingleDocument:url];
}
urlString = nil;
url = nil;
[self dismissModalViewControllerAnimated:YES];
}
- (void)downloadSingleDocument:(NSURL *)url
{
NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];
[req addValue:#"Basic XXXXXXX=" forHTTPHeaderField:#"Authorization"];
downloadConnection = [[NSURLConnection alloc] initWithRequest:req delegate:self startImmediately:YES];
}
- (void)connection:(NSURLConnection *)conn didReceiveResponse:(NSURLResponse *)response
{
if (conn == downloadConnection) {
NSString *filename = [[conn.originalRequest.URL absoluteString] lastPathComponent];
filename = [filename stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
filePath = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:filename];
[[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
file = [[NSFileHandle fileHandleForUpdatingAtPath:filePath] retain];
if (file)
{
[file seekToEndOfFile];
}
}
}
- (void)connection:(NSURLConnection *)conn didReceiveData:(NSData *)data
{
if (conn == downloadConnection) {
if (file) {
[file seekToEndOfFile];
}
[file writeData:data];
}
}
- (void)connectionDidFinishLoading:(NSURLConnection *)conn
{
if (conn==downloadConnection) {
[file closeFile];
}
}
And my problem is that only the last file is downloaded. Any suggestions on what I am doing wrong?
Thanks in advance for help!

Answer 1

The problem is that you "overwrite" the member var "downloadConnection" within your loop with a new instance of NSURLConnection (through method call downloadSingleDocument). Doing this leads to the case that the if-statements within your didReceiveResponse, didReceiveData and connectionDidFinish methods will only evaluate to true with the latest created connection. Try using a list of connections to avoid this.