Question

I currently have a UIViewController and a NSObject class.

What i want to do is to tell the NSObject class to perform an action and then tell the UIViewController when it has finished it’s action.

I’m calling the object to perform it’s action like so:

[fooObject performActionWithDelegate:self];

The performActionWithDelegate function basically only takes the UIViewcontroller’s delegate to perform a callback.

-(void)performActionWithDelegate:(id)d{

    // bar is declared in the fooObject header file
    // id bar;

    [bar setDelegate:d];

    [bar performCallback];

}

Where performCallback is a simple NSLog()-statement in the UIViewController:

-(void)performCallback{

    NSLog(@"Successfully performed a callback");    

{

Now, i’d like this to work. My first guess is that this is not the best approach to this problem.

The full scope of the problem is that the fooObject is supposed to perform a httppost to a webservice to update one of it’s properties and then inform the uiviewcontroller if the operation was successful or not.

How do i achieve this?

Any tips and/or pointers will be highly appreciated!

Thanks in advance.

Edit:
The actual problem is that the fooObject is not performing the callback.

Answer 1

Its not clear exactly what you are trying to accomplish. What you are doing seems related to two different design patterns:

• Delegate
• Asynchronous callback

Delegate: You would use a delegate if there is some reason to separate out some of the functionality of your UIViewController into another object. Instead of the UIViewController doing something it asks another object to do it. This is commonly used for code reuse so you can have the same UIViewController serve in different cases and just change the delegate to change some of its behavior.

Asynchronous callback: This allows an operation to occur in the background while you are doing other things and then be notified by calling a method of your object when the operation completes. You can do this without involving other objects.

In your case, why do you want to perform an HTTP post to a web service outside of our UIViewController? Do you just want to separate the network code from UI code? In this case, you don’t really need a delegate, just call the method on the other object from your UIViewController and when it returns, its done. It can pass back any result you need in other parameters. Returning values by setting properties on the calling object is not generally a very good design. Even if you do this the UIViewController isn’t really a “delegate”.

On the other hand if you are concerned about blocking the main thread while the HTTP post is in process then you will want to use something like asynchronous callback. The easiest way to do this is to use Grand Central Dispatch. Conceptually you could do something like this:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
  [self doLongHTTPPost];
  dispatch_async(dispatch_get_main_queue(), ^{ [self longHTTPPostDone]; });
});

This will call doLongHTTPPost in the background and then at some later time after it is complete it will call longHTTPPostDone on the main thread where it is safe to take UI actions.