incompatible Objective-c types warning - objective-c

Question

I have a user class that I use through the iPhone application, this is the init and initWithUser functions from my user class (A SUBCLASS OF NSobject), when I use the initWithUser function I get the warning described after the code. please advise.
// serialize.h
#import <Foundation/Foundation.h>
#protocol Serialize
// serialize the object to an xml string
-(NSString*)ToXML;
#end
// user.h
#import <Foundation/Foundation.h>
#import "Serialize.h"
#import "Contact.h"
#interface User : NSObject <Serialize> {
NSString *email;
NSString *firstName;
NSString *lastName;
NSString *userId;
NSString *userName;
NSString *password;
NSMutableArray *contactList;
}
#property (nonatomic,copy) NSString *email;
#property (nonatomic,copy) NSString *firstName;
#property (nonatomic,copy) NSString *lastName;
#property (nonatomic,copy) NSString *userId;
#property (nonatomic,copy) NSString *userName;
#property (nonatomic,copy) NSString *password;
#property (nonatomic, retain) NSMutableArray *contactList;
//-(id)init;
-(id)initWithUser:(User *)copyUser;
#end
// user.m
#import "user.h"
#implementation User
#synthesize email;
#synthesize firstName;
#synthesize lastName;
#synthesize userId;
#synthesize userName;
#synthesize password;
#synthesize contactList;
-(id)init
{
// call init in parent and assign to self
if( (self = [super init]) )
{
// do something specific
contactList = [[NSMutableArray alloc] init];
}
return self;
}
-(id)initWithUser:(User *)copyUser
{
if( (self = [self init]) ) {
email = copyUser.email;
firstName = copyUser.firstName;
lastName = copyUser.lastName;
userId = copyUser.userId;
userName = copyUser.userName;
password = copyUser.password;
// release contactList initialized in the init
[contactList release];
contactList = [copyUser.contactList mutableCopy];
}
return self;
}
- (void)dealloc
{
// TODO:
[contactList removeAllObjects];
[contactList release];
[super dealloc];
}
// implementation of serialize protocol
-(NSString*)ToXML
{
return #"";
}
and I use it in the main controller this way
- (void) registerNewUser {
RegistrationViewController *regController = [[RegistrationViewController alloc] init] ;
regController.newUser = [[User alloc] initWithUser:self.user];
[self.navigationController pushViewController:regController animated:YES];
[regController release];
}
the line
regController.newUser = [[User alloc] initWithUser:self.user];
gives me the following error, and its been driving me nuts for a couple of days:
incompatible Objective-c types 'struct User*', expected 'struct NSString *' when passing argument 1 of 'initWithUser:' from distinct Objective-c type
any help and guidance is appreciated

Answer 1

The problem is you have an ambiguous selector. Because alloc returns id, the call to initWithUser: has become ambiguous. NSUserDefaults also has an initWithUser: function which takes a string. The compiler thinks you're trying to use that one. Change the line to
regController.newUser = [(User*)[User alloc] initWithUser:self.user];
and everything should work as expected.

Answer 2

As mentioned in the comments, there are other problems with your implementation. In your initializer, reusing the -init is redundant and the assignments to ivars like email should be taking ownership of the data using -copy or -retain:
-(id)initWithUser:(User *)copyUser {
if((self = [super init])) {
// take ownership of the users data by copying or retaining:
email = [copyUser.email copy];
// ...
contactList = [copyUser.contactList mutableCopy];
}
return self;
}
In -dealloc, -removeAllObjects can be removed and the member data has to be released:
- (void)dealloc {
[email release];
// ...
[contactList release];
[super dealloc];
}
Note that you are also leaking the new User instance if newUser is a copy or retain property as there is a release missing:
User *user = [[User alloc] initWithUser:self.user];
regController.newUser = user;
[user release];