Slow Multiple URL retreival in iOS code - objective-c

Question

I want to access a URL and retrieve data from this URL, based on the data retrieved I want to retrieve data from another URL
I tried accessing multiple URL in the following way:
- (void) showClassRoom:(NSString *)theMessage{
NSString *queryURL =[NSString stringWithFormat:#"http://nobert.cloudfoundry.com/CalOfEvents/tos"];
NSURL *url = [NSURL URLWithString: queryURL];
NSURLRequest *req = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
NSError *error;
NSURLResponse *response;
NSData *returnData = [NSURLConnection sendSynchronousRequest:req returningResponse:&response error:&error];
if(returnData){
NSString *strResult = [[NSString alloc] initWithBytes:[returnData bytes] length:[returnData length] encoding:NSUTF8StringEncoding];
NSDictionary *result = [strResult JSONValue];
for(id theKey in result){
for(id hello in theKey){
NSLog(#"The key:%#, The value:%#",hello,[theKey objectForKey:hello]);
}
}
if(TRUE){//based on some condition secondShowClassRoom is called
[self secondShowClassRoom];
}
}
}
- (void) secondShowClassRoom{
NSString *queryURL =[NSString stringWithFormat:#"http://nobert.cloudfoundry.com/CalOfEvents/to"];
NSURL *url = [NSURL URLWithString: queryURL];
NSURLRequest *req = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
NSError *error;
NSURLResponse *response;
NSData *returnData = [NSURLConnection sendSynchronousRequest:req returningResponse:&response error:&error];
if(returnData){
NSString *strResult = [[NSString alloc] initWithBytes:[returnData bytes] length:[returnData length] encoding:NSUTF8StringEncoding];
NSDictionary *result = [strResult JSONValue];
for(id theKey in result){
for(id hello in theKey){
NSLog(#"The key:%#, The value:%#",hello,[theKey objectForKey:hello]);
}
}
}
}
This retrieves the data VERY SLOWLY and my app requires very fast access as I am developing an application on Augmented Reality
There is another method that is faster however I am not able to access multiple URLs:
- (void) showClassRoom:(NSString *)theMessage{
NSString *queryURL =[NSString stringWithFormat:#"http://nobert.cloudfoundry.com/CalOfEvents/to"];
NSURL *url = [NSURL URLWithString: queryURL];
NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];
conn = [[NSURLConnection alloc] initWithRequest:req delegate:self];
if (conn) {
webData = [[NSMutableData data] retain];
}
classRoomControl.hidden = NO;
labControl.hidden = YES;
placementControl.hidden = YES;
}
-(void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *) response{
[webData setLength: 0]; }
-(void) connection:(NSURLConnection *)connection didReceiveData:(NSData *) data {
[webData appendData:data];
}
-(void) connection:(NSURLConnection *)connection didFailWithError:(NSError *) error {
[conn release];
[webData release];
}
-(void) connectionDidFinishLoading:(NSURLConnection *) connection {
[conn release];
NSLog(#"DONE. Received Bytes: %d", [webData length]);
NSString *strResult = [[NSString alloc] initWithBytes:[webData mutableBytes] length:[webData length] encoding:NSUTF8StringEncoding];
NSDictionary *result = [strResult JSONValue];
for(id theKey in result){
for(id hello in theKey){
NSLog(#"The key:%#, The value:%#",h,hello);
}
}
[strResult release];
[webData release];
}
Please Help me with this.Any help would be appreciated..

Answer 1

You are right on track preferring the asynchronous model for network communication (since synchronous communication will block your UI unless you handle it in a separate thread).
The correct way to chain multiple asynchronous network request is doing one request after another in the callbacks (i.e., in connectionDidFinishLoading; when one request is done, you send the next one).
One more suggestion is not using NSURlRequest/NSURLConnection for that, since they make thinks unnecessarily complex, and try with a framework like AFNetworking.