How to know if data is present in url are not - iphone

Question

I have written code like this but I can't understand how to find if the data is present or not in the URL. Can anyone help me in solving this problem?
Note: This code terminates when the loop is entering the second condition. That is where it's terminating.
-(void)getdetails
{
NSLog(#"in get details");
NSURL *jsonurl=[NSURL URLWithString:#"http://www.myappdemo.com/checkout/services/getonlineusers.php"];
NSMutableURLRequest *request=[[[NSMutableURLRequest alloc]init ]autorelease];
[request setURL:jsonurl];
[request setHTTPMethod:#"POST"];
[request setValue:#"application/x-www-form-urlencoded" forHTTPHeaderField:#"Content-Type"];
NSError *error;
NSURLResponse *response;
NSData *serverReply = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
NSString *replyString = [[NSString alloc] initWithBytes:[serverReply bytes] length:[serverReply length] encoding: NSASCIIStringEncoding];
if([replyString isEqualToString:#"Invalid."]){ // i have not set the php code to output "invalid" so this will not work for now ...
NSLog(#"%#",replyString);
}
else {
NSMutableArray *tempArray =[replyString JSONValue];
int count=0;
self.temparray=tempArray;
for(int i=0;i<[tempArray count];i++)
{
///////Here in this loop when it is entering it is terminating /////////
NSDictionary *dict=[tempArray objectAtIndex:i];
NSLog(#"DICT is %#",dict);
NSString *string=[dict objectForKey:#"profilepic"];
NSURL *finalURL = [NSURL URLWithString:[string stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding]];
NSLog(#"encoding string is %#",finalURL);
NSURL *url=[NSURL URLWithString:string];
NSString *source = [NSString stringWithContentsOfURL:finalURL encoding:NSUTF8StringEncoding error:nil];
NSFileManager *fileManager = [NSFileManager defaultManager];
BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:url];
NSLog(#"url is %#",url);
NSData *data=[NSData dataWithContentsOfURL:url];
if(!(data==nil))
{
NSLog(#"data is there");
UIImage *image=[[UIImage alloc]initWithData:data];
[self.array addObject:image];
[image release];
}
else {
/*
NSLog(#"if data is null condition block");
UIImage *image=[[UIImage alloc]init];
[self.array addObject:image];
[image release];
*/
}
count=count+1;
NSLog(#"count is %d",count);
}
}
[replyString release];
}

Answer 1

Where does the app terminate and what is the exception? Have you stepped through to see what the array object looks like during each iteration? Is it failing at NSData initWithContentsOfURL? Why don't you issue that as a separate synchronous request and test to see if you got a response?
Regarding your first (and any subsequent) synchronous request, it would probably be good to add a check to ensure you received a valid response (sorry for the formatting, the code tag isn't playing nicely at the moment)
if (response!=nil) {if([response isKindOfClass:[NSHTTPURLResponse class]]) {
// you have a valid response }}