Can I load multiple UIViewControllers that each kick off their own NSURLConnections?

My Rootviewcontroller uses NSURLConnection to get data from a server, and then, based on this data, loads a bunch (开发者_如何转开发like 7) of smaller UIViewControllers that each also use their own NSURLConnection to get some more specific data from the server. But, the problem is, only the RooTViewController is recieving callbacks from:

- (void)connectionDidFinishLoading:(NSURLConnection *)theConnection

the other UIViewControllers never get callbacks...

You should really work with the assumption that only one view controller is active at the time. So if you want the other view controllers to do work, even when they are not visible on the screen, then you should move that logic into some singleton object that does all the network communication. The viewcontroller, when they appear, will simply ask this object for the data.

For the iPhone it is a really bad design to let inactive view controllers do stuff in the background. The only thing they do is manage the view that you currently see on the screen.

@St3fan is correct about good patterns for UIViewController. Many a developer has been burned thinking his UIViewController always has a non-nil view (it doesn't).... Even so, I'll discuss here what may be going wrong.

There are two likely causes: you're not setting the UIViewControllers as the delegates of their NSURLConnections, or you're not actually starting the NSURLConnections. The most likely cause of the latter is that you're using NIBs and expecting them to load at the beginning of the program, when they actually only load when needed.

As @deanWombourne notes, you can have all the NSURLConnections you want (**). Walk through your code in the debugger. Make sure you're not sending messages to nil. When "nothing happens" it almost always means you're sending messages to nil.

(**) Don't get crazy with connections on iPhone. Network connections are expensive to create (in both time and battery). If you can get all the data you need over a single connection, there are some advantages to doing so. This doesn't mean you should bend over backwards to avoid connections; just be careful of letting them get out of control.