Using selectors for callbacks?

Question

hi, I think i should be using selectors (or even a different paradigm), but even after R'ing TFM I can't figure out what i'm supposed to do. It's all related to callbacks from a delegate

I have my main Model object:

    @implementation Model
    @synthesize myConnection; // which is an NSURLConnection
    ...
    -(void)someMethod{
    MyConnectionDelegate *mcd = [[MyConnectionDelegate alloc]initWithCallingObject:self];
    myConnection = [[NSURLConnection alloc] initWithRequest:requestForToken delegate:mcd];
...
}
-(void)didGetCalledBack:(NSArray *)resultArray{
  NSLog(@"got the callback");
}

and then in my delegate:

@implementation MyConnectionDelegate
@synthesize callingObject; // which is of type id
@synthesize resultArray; // NSArray
-(id)initWithCallingObject:(id)caller{
  ...//std [self init] block
  self.callingObject  = caller;
  return self;
...
}


-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
...
}
//and all the other NSURLConnection delegate methods


- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
  ...
  // finish building array of results into self.resultArray
  [self.callingObject didGetCalledBack:self.resultArray];
}

So... 1) I think i should be using selectors, or something else rather than hardcoding the fact that the caller (delegator?) needs to implement -didGetCalledBack: Right? IF so, how? (and why, other than cleanliness)

2) Or is my whole implementation wrong in the way i'm attempting to use a callback from the delegate of the NSURLConnection back to the delegator wrong?

I've looked at the Apple samplecode etc but nothing i've seen ever has anything other than delegate:self. Maybe i should have delegate:self too for the NSURLConnection, but I'm making many connections and if i do delegate:self my delegate methods (like -didReceiveData:) become a big mess of if (connection ==connection1){ type code.

thanks, richard

Answer 1

Maybe i should have delegate:self too for the NSURLConnection, but I'm making many connections and if i do delegate:self my delegate methods (like -didReceiveData:) become a big mess of if (connection ==connection1){ type code.

Then don't use explicit comparisons - use containers or similar abstractions to react to different connections.

E.g. to use the results of connections with different controls, use a dictionary that maps from NSURLConnections to those controls so the following:

if      (connection == connection1) [obj1 doStuff];
else if (connection == connection2) [obj2 doStuff];
// ...

becomes:

[[connectionClients objectForKey:connection] doStuff];

Answer 2

I think i should be using selectors, or something else rather than hardcoding the fact that the caller (delegator?) needs to implement -didGetCalledBack: Right? IF so, how? (and why, other than cleanliness)

Nothing wrong with what you are doing. You might want to consider declaring a protocol for a calling object e.g.

@protocol CallingObject <NSObject>
    -(void) didGetCallBack: (NSArray*) resultArray;
@end

And then

@interface Model : NSObject <CallingObject> // ...

and

@interface MyConnectionDelegate : NSObject
{
    // ...
}

-(id) initWithCallingObject: (id<CallingObject>) calller;

// ...

@end

That will give you some compile time checking that the calling object implements the required method(s).