Using multiple NSURLConnections at the same time - best practices

In my iPhone app, I've been able to use NSURLConnection properly to download data from a URL. I simply set the delegate to my UIView, and make sure that I set up the UIView to answer for the proper delegate functions such as -connection:didReceiveResponse:. However, if I have a number of NSURLConnections (either for a similar type of request, or multiple kinds of requests), it gets messy because the delegate functions, such as didReceiveRequest, don't differentiate between the different requests. The advantage of asynchronous requests is that you are supposed to be 开发者_如何学JAVAable to multiple at once, without blocking the main thread. What's the best practice for how to use multiple NSURLConnection requests at the same time?

I prefer to wrap them in a higher-level object (like ImageDownloader or SomeWebServiceCall) that has all the per-connection/call state information. I usually create a delegate these objects so that the caller gets a more specific callback when the operation has succeeded or failed.

Perhaps look into ASIHTTPRequest, instead of NSURLConnection. ASIHTTPRequest makes a lot of this work trivially easy.

In this case, I'd say NSOperation is your best bet. ASIHTTPRequest is based on NSOperation and allows you to handle each request as an operation, which serves as the delegate for its own NSURLConnection.

You'll have to be careful here though, because by default NSOperations are run on separate threads, but some APIs, like this one, are required to be executed on the main thread. If you inspect the source code to ASIHTTPRequest you'll notice they've got some infrastructure to ensure delegate methods are called on the main thread.

Create an instance variable for each NSURLConnection and NSMutableData. All of your delegate methods have the NSURLConnection object as an argument, so you can match them as such:

-(void)connectionDidFinishLoading:(NSURLConnection *)connection {
    if (connection == aConnection) {

       // Do something with the data for aConnection

    } else if (connection == otherConnection) {

       // Do something with the data for otherConnection

    }
}

This still limits you to one connection per instance variable, so it's not suitable for, for instance, a table view with images on each row that need to be loaded.