Design pattern for handling a server response - objective-c

Question

I've an observer pattern on the UI that checks what's the status of an object that handles a server connection that's trying to update a certain field on a database.
The UI's update method receives an object containing data pairs containing the information of what's happening with the connection. The problem is that I'm getting tangled with a lot of ifs checking for different possibilities.
- (void) update:(Bundle *)arg
{
if ([[arg getData:#"updatee"] isEqualToString:#"email"]){
UITableViewCell *emailCell = [[self tableView] cellForRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]];
if ([[arg getData:#"connecting"] isEqualToString:#"true"]) {
//Email is being posted
[_emailLabel_email setText:#"Connecting..."];
[_emailLabel_set setHidden:YES];
emailCell.accessoryType = UITableViewCellAccessoryNone;
[_emailActivityIndicator startAnimating];
}else{
if ([[arg getData:#"succesfull"] isEqualToString: #"false"])
//Email was posted unsuccesfully
[[[UIAlertView alloc] initWithTitle:#"Taken Email Address"
message:#"The email address that you entered is already in use, please double check it"
delegate:nil
cancelButtonTitle:#"OK"
otherButtonTitles:nil] show];
else{
//Email was posted succesfully.
[_emailLabel_set setText:#"Change"];
}
[_emailActivityIndicator stopAnimating];
[_emailLabel_email setText:[mng getEmail]];
[_emailLabel_set setHidden:NO];
emailCell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
}
}
//Password cases
}
}
As the server responds with a string I'm finding difficult to avoid this spaggetti of code.
Which would be the smarter object to send on the update method?

Answer 1

You could keep the data how it is and put all of the values you expect for [arg getData:#"updatee"] as the keys in a dictionary. The values would be the string representation of method selectors, where each of the methods handles one of the cases in your current if statement. Now your update: method just gets the selector string from the dictionary, converts it to a real selector (NSSelectorFromString) and calls the method (passing the arg as a parameter, all methods used here must have matching parameter listing). If you receive an unexpected update type nothing would happen so you should log / assert that. If you get an exception while translating the selector you probably have a typo (good candidate for a test which executes all of the methods in the configuration).
Of course you could basically do the same thing with all the methods and a dirty big if / else statement.