How to make program wait for asynchronous NSURLConnection to finish before proceeding with next command?

Question

How can I make my program wait for an asynchronous NSURLConnection to finish before going to the next line of code?

SetDelegate *sjd= [SetDelegate alloc];
NSURLC         


        

Answer 1

If you just want to know when it's complete and don't really care about any data, simply use the NSNotificationCenter to post a notification and have your view subscribe to it.

Delegate - Post Notification upon completion

-(void) connectionDidFinishLoading:(NSURLConnection*)connection {
    [[NSNotificationCenter defaultCenter] postNotificationName:@"NSURLConnectionDidFinish" object:nil];
}

View - Add observer and run some code when observed

-(void) viewDidLoad {

[[NSNotificationCenter defaultCenter] addObserver:self
                                          selector:@selector(yourCleanupMethod)
                                               name:@"NSURLConnectionDidFinish"
                                              object:nil];
}

-(void) yourCleanupMethod {
    // finish up

    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

Now, if you need to pass a simple object back as data you can try loading up the object parameter in your notification like this:

[[NSNotificationCenter defaultCenter] postNotificationName:@"NSURLConnectionDidFinish" object:yourDataObject];

Then change your view and cleanup signature like this:

-(void) viewDidLoad {

// Notice the addition to yourCleanupMethod
[[NSNotificationCenter defaultCenter] addObserver:self
                                          selector:@selector(yourCleanupMethod:)
                                               name:@"NSURLConnectionDidFinish"
                                              object:nil];
}

-(void) yourCleanupMethod:(NSNotification *)notif {
    // finish up
    id yourDataObject = [notif object];

    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

Now I found myself needing something a little more than this so I ended up creating a singleton to handle all of my requests. Since all of your delegate methods in NSURLConnectionDelegate give you and instance of the NSURLConnection for the specific connection, you can simply store a mutable data object in a dictionary and look it up each time by the connection. From there I have a method signature that takes and object and selector in that I associate with the connection so after everything has wrapped up, I can pass that mutable data object to the requestor by performing the selector on that object.

I won't include all of that code here but maybe that will help get you thinking about what is possible. I found that I had a lot of code tied up in making web service calls so wrapping everything up in a singleton gave me a nice clean way of getting data. Hope this helps!