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Custom NSURLConnection class with tag

A caveat one quickly encounters when using multiple asynchronous NSURLConnections with the same target delegate is that there is no easy way to distinguish one connection from the other, in for instance the connection:didReceiveData: method.

Since using multiple asynchronous connections implies handling the received data chunks yourself, one is likely to create a dictionary which contains a NSMutableData object for each NSURLConnection key. Unfortunately does a NSDictionary copy its keys and this is not something a NSURLConnection supports. A quick solution to avoid this is to make a subclass with a tag to distinguish each connection. This tag can be used as key in the dictionary.

Interface:

@interface CustomURLConnection : NSURLConnection {
   NSString *tag;
}
 
@property (nonatomic, retain) NSString *tag;
 
- (id)initWithRequest:(NSURLRequest *)request delegate:(id)delegate startImmediately:(BOOL)startImmediately tag:(NSString*)tag;
 
@end

Implementation:

@implementation CustomURLConnection
 
@synthesize tag;
 
- (id)initWithRequest:(NSURLRequest *)request delegate:(id)delegate startImmediately:(BOOL)startImmediately tag:(NSString*)tag {
   self = [super initWithRequest:request delegate:delegate startImmediately:startImmediately];
 
   if (self) {
      self.tag = tag;
   }
   return self;
}
 
- (void)dealloc {
   [tag release];
   [super dealloc];
}
 
@end

As you can see, creating a subclass with a tag property is rather easy and solves the dictionary issue.

Tags:

This entry was posted on Monday, March 2nd, 2009 at 22:41 and is filed under Cocoa Touch. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

7 Responses to “Custom NSURLConnection class with tag”

  1. Cuahutleco says:
    6 October 2009 at 20:31

    Great tip!, thanks!

  2. Hasnat says:
    10 December 2009 at 19:00

    add this to implementation of CustomURLConnection

    - (NSString *)tag {
    return tag;
    }
    as if you try to get it by cURLConnectionvar.tag it gives error in didReceiveResponse and didReceiveData etc functions
    so use [cURLConnectionvar tag]
    gives a warning but should work

    thanks for the code

  3. Andreas Monitzer says:
    2 February 2010 at 16:56

    What about using [NSValue valueWithNonRetainedObjectValue:] for the key? That would solve the issue as well.

  4. Georg says:
    27 February 2010 at 15:21

    hi, this is what I am really looking for, a multiple download method!!
    I just see a light in the tunnel, but, my question is, how to add these codes to an UITableViewController ?

    because in your example :
    @interface CustomURLConnection : NSURLConnection {
    NSString *tag;
    }
    it’s different to my app, how to implement this to my code below:
    @interface LessonSubViewController : UITableViewController{

    }
    @end

    any idea??

  5. Yannick Compernol says:
    16 March 2010 at 23:00

    @Georg: You would create an instance of CustomURLConnection in the ViewDidLoad method of your LessonSubViewController controller. You would use this CustomURLConnection to load the data & once it is received update the table with the new data.

  6. Yannick Compernol says:
    16 March 2010 at 23:03

    @Andreas Monitzer: I didn’t know that existed to be honest and it looks indeed like that could work. Thanks for bringing that up!

  7. EricS says:
    28 March 2010 at 00:41

    I just used an NSValue as the dictionary key, using the NSConnection pointer.:

    + (NSValue *)valueWithPointer:(const void *)pointer;

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