Question

my app is using network connections as in here:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{ 
    .
    .
    .
    receivedData = [[NSMutableData alloc] init];
}

.

-(void) dataFromWeb{
request = [[NSURLRequest alloc] initWithURL: url];
theConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

if (theConnection) {
    receivedData = [[NSMutableData data] retain];
    NSLog(@"** NSURL request sent !");
} else {

    NSLog(@"Connection failed");
}

.

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    .
    .
    .
    [theConnection release];
    [request release];

// Here - using receivedData
[receivedData release];
}

.

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
      [receivedData setLength:0];
}

.

- (void)connection:(NSURLConnection *)connection
  didFailWithError:(NSError *)error
{
    [theConnection release];
    [request release];
    [receivedData release];
}

.

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

. Down the road in the app is this snippet (onButtonPressed):

if (theConnection) {
    // Create the NSMutableData to hold the received data.
    // receivedData is an instance variable declared elsewhere.
    receivedData = [[NSMutableData data] retain];
} else {
    NSLog(@"Connection failed");
}

What I want to understand is:

• If I wanted to create another simultaneous URLRequest, would I need to use a different connection so that data arriving from the web won’t mix up upon retrieval?

• In this code, what happens is that sometimes the code would crash on the line of the function didReceiveResponse() setLength:0, when the app crashed I saw receivedData=nil should I change the line to

  if(receivedData!=nil)
     [receivedData setLength:0];
  else
     receivedData = [[NSMutableData data] retain];
  

• I am not so sure what this line is doing receivedData = [[NSMutableData data] retain];

Answer 1

I think that the easiest way to handle 2 connections is duplicating the NSMutableData. I use in that way, and it works perfectly for me.

Fist you do this in the point you want the second connection:

receivedData2 = [[NSMutableData alloc] init];

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response  
{  
    if (receivedData2) {
        [receivedData2 setLength:0];  
    }
    else 
    {
        [receivedData setLength:0];  
    }
}  

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data  
{  
    if (receivedData2) {
        [receivedData2 appendData:data];  
    }
    else {    
        [receivedData appendData:data]; 
    }
} 

And then, in the method you ask for receivedData2 or receivedData

And when you use it don´t forget to do:

receivedData2=nil;
[receivedData2 setLength:0];