Question

First off good day and thanks for taking the time to answer my question.

Some background:
I have done the same thing in a regular OS X program in that I run everything in main.m

What I’m doing:

making a VERY crude app that adds a FirstName and LastName text field. The user enters some text and when they press add to address book the program gets the string info and adds it to a NSMutableArray

like i said VERY crude but for learning purposes.

What’s wrong:

AddressBook.h and AddressBook.m files

AddressBook.h

#import <Foundation/Foundation.h>

@interface AddressBook : UIViewController
{
    NSMutableArray *nameArray;

}

@property (nonatomic, copy) NSMutableArray *nameArray;


@end

---

AddressBook.m

#import "AddressBook.h"

@implementation AddressBook
@synthesize nameArray;
@end

---

side notes and comments

So I get that I create a class called AddressBook and it has a NSMutableArray

I know that if I wanted to create a new object that is part of AddressBook class I would call it in main.m like this
AddressBook *newAddressBook = [AddressBook new];
newAddressBook.nameArray = [NSMutableArray array];
then i could do what I want. I have successfully made a program like this but not an iPhone version.

---

BIDViewController.h

#import <UIKit/UIKit.h>
#import "AddressBook.h"
@interface BIDViewController : UIViewController
{
    AddressBook *myBook;
    UITextField *firstNameField;
    UITextField *lastNameField;
    NSString *tester;
    id myTempBook;

}
//@property (retain, nonatomic) AddressBook *myBook;
@property (retain, nonatomic) IBOutlet UITextField *firstNameField;
@property (retain, nonatomic) IBOutlet UITextField *lastNameField;
@property (copy, nonatomic) NSString *tester;
@property (retain, nonatomic) id myTempBook;
- (IBAction)addToAddressButton:(id)sender;
- (IBAction)textFieldDoneEditing:(id)sender;
- (IBAction)displayAddress:(id)sender;

@end

---

BIDViewController.m

#import "BIDViewController.h"
@implementation BIDViewController
@synthesize lastNameField, firstNameField, tester;
//@synthesize myBook;
@synthesize myTempBook;



- (IBAction)textFieldDoneEditing:(id)sender
{
    //keyboard stuff
    //give control back to view
    [sender resignFirstResponder];
}
- (IBAction)displayAddress:(id)sender
{
    //display address book array
}
- (IBAction)addToAddressButton:(id)sender
{

    //add the names to array
    //here is what I want to do
    [myBook.nameArray addObject:lastNameField.text];

    //ever time I NSLog the array with objectAtIndex:0 
    //it returns null.  I've tried EVERY combinations of stuff I even tried
    //allocating a new array
   //such as myBook.nameArray = [NSMutableArray array]; and I still could not return anything but null :( 

}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    //myBook.nameArray = [NSMutableArray array];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end

---

My Question:

what am I doing wrong because I have accomplished this exact same concept but running the program in main.m.

I think I understand what is going on…

1. iPhone program loads the BIDViewController when the user clicks on the app icon.
2. since BIDViewController gets initialized it creates myBook which is an object in class AddressBook. it is automatically getter and setter with @synthesize
3. my BIDViewController sees that it is created and I can write to the array with no problem however somewhere along the way I keep getting null returns.

---

Other side notes

I can share my program where I have successfully accomplished what I wanted in a non iPhone app but a simple command console version.

Answer 1

At no point do you create myBook. It will always be nil, so you won’t ever be able to do anything with its array property.

Just declaring a property and synthesising the accessors doesn’t automatically create you an object. You must create the object and assign it to your property, which you mention doing but do not have in your code.

In addition, there seems no good reason why address book would inherit from UIViewController. It seems like a model object, it should probably inherit from NSObject.