Objective-c – Managing multiple asynchronous NSURLConnection connections

cocoacocoa-touchiphonensurlconnectionobjective c

I have a ton of repeating code in my class that looks like the following:

NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request
                                                              delegate:self];

The problem with asynchronous requests is when you have various requests going off, and you have a delegate assigned to treat them all as one entity, a lot of branching and ugly code begins to formulate going:

What kind of data are we getting back? If it contains this, do that, else do other. It would be useful I think to be able to tag these asynchronous requests, kind of like you're able to tag views with IDs.

I was curious what strategy is most efficient for managing a class that handles multiple asynchronous requests.

Best Answer

I track responses in an CFMutableDictionaryRef keyed by the NSURLConnection associated with it. i.e.:

connectionToInfoMapping =
    CFDictionaryCreateMutable(
        kCFAllocatorDefault,
        0,
        &kCFTypeDictionaryKeyCallBacks,
        &kCFTypeDictionaryValueCallBacks);

It may seem odd to use this instead of NSMutableDictionary but I do it because this CFDictionary only retains its keys (the NSURLConnection) whereas NSDictionary copies its keys (and NSURLConnection doesn't support copying).

Once that's done:

CFDictionaryAddValue(
    connectionToInfoMapping,
    connection,
    [NSMutableDictionary
        dictionaryWithObject:[NSMutableData data]
        forKey:@"receivedData"]);

and now I have an "info" dictionary of data for each connection that I can use to track information about the connection and the "info" dictionary already contains a mutable data object that I can use to store the reply data as it comes in.

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    NSMutableDictionary *connectionInfo =
        CFDictionaryGetValue(connectionToInfoMapping, connection);
    [[connectionInfo objectForKey:@"receivedData"] appendData:data];
}

Related Solutions

R – Dealing with variable assignments and async requests

I solved this problem a couple ways in different apps.

One solution is to pass an object and selector along to notify such as:

- (id)getUsersAndNotifyObject:(id)object selector:(SEL)selector

This breaks the nice property behavior however. If you want to keep the methods as properties, have them return immediately, with either cached data or nil. If you need to go out to the network, do so asynchronous and then let the rest of the app know the data changed via KVO or the NSNotificationCenter. (Cocoa Bindings would be an option on the Mac, but they don't exist on iPhone).

The two methods are fairly similar. Register for updates with your shared instance, and then ask for the data. KVO is a little lighter weight if you just dealing with raw observable properties, but an NSNotification might be more convenient if you're interested in several different pieces of data.

With an NSNotification, the client object could register for one type of notification which includes the changed data in its userInfo dictionary instead of having to register obvservers for every single key path you're interested in.

An NSNotification would also allow you to pass back failures or other status information a lot more easily than straight KVO.

KVO method:

// register observer first so you don't miss an update
[[MySingleton sharedInstance] addObserver:self
                               forKeyPath:@"users"
                                  options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld)
                                  context:&kvo_users_context];
 users = [MySingleton sharedInstance].users;

 // implement appropriate observeValueForKeyPath:ofObject:change:context: method

NSNotification Method:

 [[NSNotificationCenter defaultCenter] addObserver:self
                                          selector:@selector(sharedDataChanged:)
                                              name:MySingletonDataUpdatedNotification
                                            object:[MySingletonDataUpdatedNotification sharedInstance]];
 users = [MySingleton sharedInstance].users;

 // implement appropriate sharedDataChanged: method

Iphone – Changing the userAgent of NSURLConnection

Obj-C:

NSString* userAgent = @"My Cool User Agent";
NSURL* url = [NSURL URLWithString:@"http://whatsmyuseragent.com/"];
NSMutableURLRequest* request = [[[NSMutableURLRequest alloc] initWithURL:url]
                                autorelease];
[request setValue:userAgent forHTTPHeaderField:@"User-Agent"];

NSURLResponse* response = nil;
NSError* error = nil;
NSData* data = [NSURLConnection sendSynchronousRequest:request
                                     returningResponse:&response
                                                 error:&error];

Swift:

let userAgent = "My Cool User Agent"
if let url = NSURL(string: "http://whatsmyuseragent.com/") {
   let request = NSMutableURLRequest(URL: url)
   request.setValue(userAgent, forHTTPHeaderField: "User-Agent")
   var response:NSURLResponse? = nil;
   var error:NSError? = nil;
   if let data = NSURLConnection.sendSynchronousRequest(request, returningResponse: &response, error: &error) {
      // do something with your data
   }
 }

Best Answer

Related Solutions

R – Dealing with variable assignments and async requests

Iphone – Changing the userAgent of NSURLConnection

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