incompatible Objective-c types warning

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开发者_如何学编程;
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

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.

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];