Inheritance not working..

Question

Hi!
I would like to clean my code.. There are several connection classes, which all have the same methods. so, inheritance is the choice. for e.g., all my classes start with and use "initWithDelegate".
now, my new parent connection class holds this method, and I am deleting this method from my child classes;
- (id)initWithDelegate:(id)delegate;
Connection.h
@interface Connection : NSObject {
id _delegate;
NSURLConnection *connection;
- (id)initWithDelegate:(id)delegate;
@property (nonatomic, retain) id _delegate;
@property (nonatomic, retain) NSURLConnection *connection;
@end
Connection.m
/* CONSTRUCTOR METHODS */
- (id)initWithDelegate:(id)delegate
self = [super init];
if (self)
_delegate = delegate;
return self;
but: if I am trying to use it (from a child class)
@interface LoginConnection : Connection
it compiles without warnings, but it does not work;
loginConnection = [[LoginConnection alloc] initWithDelegate:self];
error:
* -[LoginConnection initWithDelegate:]: unrecognized selector sent to instance 0x5807ab0
2010-03-27 13:43:39.030 Airwriting[17308:207] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -[LoginConnection initWithDelegate:]: unrecognized selector sent to instance 0x5807ab0'
so.. the compiler cant find the method..?

Answer 1

Hi Alex -
I added your Connection and LoginConnection classes to a test bed, pasting your code directly from the forum into the project files wherever applicable. I then created an instance of LoginConnection as follows:
- (void)applicationDidFinishLaunching:(UIApplication *)application {
// inheritance test for SommerAlex
LoginConnection *loginConnection = [[LoginConnection alloc] initWithDelegate:self];
NSLog(@"%s: loginConnection=%@ loginConnection._delegate=%@",
_func_, loginConnection, loginConnection._delegate);
[loginConnection release];
// [Session started at 2010-03-27 16:24:14 -0700.]
// 2010-03-27 16:24:17.066 Nav4[33562:20b] -[Nav4AppDelegate applicationDidFinishLaunching:]:
// loginConnection=<LoginConnection: 0x3d1c8b0>
// loginConnection._delegate=<Nav4AppDelegate: 0x3d1d5a0>
So it appears the behavior you're observing isn't the fault of the code you posted. If that code was pasted directly from your source files, we can probably rule out typos. Have you tried Build->Clean? Otherwise, I would focus on any related code that wasn't posted, or wasn't pasted into the forum directly from the project. Also make sure you're looking at the same files which are actually included in the project. If you have two versions of the same file in your project folder (e.g. one set of class files in the project root, and another like-named set in Classes), it might be easiest to hose all of them.
Btw, this has nothing to do with your primary problem, but it might be good to take a close look at the _delegate property declaration in your Connection class. It's unusual for a delegate property to want the retain attribute, especially if the object which creates the Connection is going to be the delegate. For example, if the Connection object is only released in dealloc, that method might never run. So after analyzing your requirements, consider changing that property attribute to assign.
- Ray