Question

So, I have a decent idea of what a delegate does, why use it, how to implement it etc. and I’m working on implementing it in one of my projects. The problem I’m trying to solve is to decouple my Controller objects from my Network Access class. In this context, the ideas get a little messy in my head.

I somehow intuitively feel that the NetworkAccessClass should be the delegate for a Controller object, because the NetworkAccessClass is acting as a helper for the Controller object. But it seems to work in a reverse fashion, because the following is apparently the right way to do it:

NetworkaccessClass.h

@protocol NetworkAccessDelegate
-(void) requestSucceded:(NSData *) data
-(void) requestFailed:(int) responseCode;
@end
@interface NetworkAccessClass : NSObject
{
    id<NetworkAccessDelegate> networkDelegate;
}

@property(nonatomic, assign) id networkDelegate;

-(void) initWithDelegate:(id) delegate; //

@end

NetworkAccessClass.m

@implementation
@synthesize networkDelegate

-(void) initWithParams:(id) delegate
{
    networkDelegate = delegate;
    // Assign GET/POST vals, create request etc
    [request startAsynchronous];    
}

-(void) requestSucceded:(ASIHTTPRequest *) request
{
    if([networkDelegate respondsToSelector:@selector(requestSucceded:)]) {
        // Send the data to the controller object for it to use
        ...
    }
}

-(void) requestFailed:(ASIHTTPRequest *) request
{
    // Same as above. Send to request failed.
}

@end 

And finally in my FirstViewController.h

#import "NetworkAccessClass.h"
@interface FirstViewController<NetworkAccessDelegate>
{

}
-(void) requestSucceded:(NSData *) data;
-(void) requestFailed:(int) responseCode;
@end

And the same in SecondViewController.h and so on.

Although this does decouple my Controllers from my Network class, I can’t help feel it’s wrong because the controllers in this case are acting as delegates or helper methods to the Network Class and not the other way round. Am I missing something basic? Or is this how it is?

Thanks,
Teja.

Answer 1

Delegates aren’t “helper methods”. Think of them as objects that get notified when something happens. (Although don’t confuse them with “Notifications”–that’s a different thing entirely.) In this case, your network class does it’s stuff and then calls its delegate method on the View Controller that instantiated and fired, it to report the contents of that response to the view controller. The controller will then, presumably, update the view with the data that the network connector got. Classic delegate pattern, right there.