How to periodically poll data from server on a background thread? - iphone

Question

I have a chat like app, and to receive periodic chats, I want to poll server at regular intervals , say 5 mins..and check if there are any new messages.
As a beginner, I have tried simple NSURLConnection and send and receive data, but stuck while polling.
What is a correct way of polling? Should I use NSTimer to poll regularly?
Is there any sample code that can help me?
I have a timer running on main thread which invokes a background thread every 5 seconds and sends request to server. Now what happening is, the delegates for NSURLConnection are not getting called. What can be done?
Please help.
Thanks

Answer 1

You can launch an NSTimer on a background thread and make calls to the main thread periodically, this is how I do it:
[self performSelectorOnMainThread:#selector(LaunchTimer) withObject:nil waitUntilDone:NO];
Just make a "LaunchTimer" function that calls an update function at a certain interval, which makes a call to NSURLConnection, and when you receive the new messages, update the chat window by making a call to the main thread like so:
[self performSelectorOnMainThread:#selector(update:) withObject:newMessages waitUntilDone:NO];

Answer 2

Continuing from answer of Patrick :- If you can try NSURLConnection without delegate,
-(void)update:(id)objmessage
{
NSString *post =[NSString stringWithFormat:#"timestamp=%#&user_id=%#",DatetimeString,UID];
NSData *postData = [post dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES];
NSString *postLength = [NSString stringWithFormat:#"%d", [postData length]];
NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];
[request setURL:[NSURL URLWithString:#"Your server URL"]];
[request setHTTPMethod:#"POST"];
[request setValue:postLength forHTTPHeaderField:#"Content-Length"];
[request setValue:#"application/x-www-form-urlencoded charset=utf-8" forHTTPHeaderField:#"Content-Type"];
[request setHTTPBody:postData];
NSError *error;
NSURLResponse *response;
NSData *returnData=[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
returnString=[[NSString alloc]initWithData:returnData encoding:NSUTF8StringEncoding];
if(!returnString)
{
UIAlertView *erroralert = [[UIAlertView alloc] initWithTitle:#"Error" message:#"There is an error getting response" delegate:self cancelButtonTitle:nil otherButtonTitles:#"OK", nil];
[erroralert show];
[erroralert release];
}
else
{
NSLog(#"%#",returnString);
}
SBJSON *json = [[SBJSON new] autorelease];
NSMutableDictionary *dic = [[NSMutableDictionary alloc] initWithDictionary:[json objectWithString:returnString error:nil]];
//NSLog(#"%#",dic);
}

Answer 3

Solved this with following method:
[self performSelectorOnMainThread:#selector(performPollinginBackground) withObject:nil waitUntilDone:NO];
-(void)performPollinginBackground{
//call server task here
}