Saving data in custom class via AppDelegate

I can't seem to save data to a custom instance object in my AppDelegate. My custom class is very simple and is as follows:

Person.h

...
@interface Person : NSObject {
    int _age;
}

- (void) setAge: (int) age;
- (int) age;
@end

Person.m

#import "Person.h"

@implementation Person

- (void) setAge:(int) age {
    _age = age;
}
- (int) age {
    return _age;
}
@end

I then create an instance of Person in the AppDelegate class:

AppDelegate.h

@class Person;

@interface AccuTaxAppDelegate : NSObject <UIApplicationDelegate> {
    ...
Person *person;
}
...
@property (nonatomic, retain) Person *person;
@end

AppDelegate.m

...
#import "Person.h"

@implementation AccuTaxAppDelegate

...
@synthesize person;

- (void)applicationDidFinishLaunching:(UIApplication *)application {

    // Override point for customization after app launch    
    [window addSubvi开发者_如何学Pythonew:[navigationController view]];
    [window makeKeyAndVisible];
}

- (void)applicationWillTerminate:(UIApplication *)application {
// Save data if appropriate
}

#pragma mark -
#pragma mark Memory management

- (void)dealloc {
    [navigationController release];
    [window release];
    [person release];
    [super dealloc];
}
@end

Finally, in my ViewController code I grab a handle on AppDelegate and then grab the person instance, but when I try to save the age it doesn't seem to work:

MyViewController

...
- (void)textFieldDidEndEditing:(UITextField *)textField
{
    NSString *textAge = [textField text];
    int age = [textAge intValue];
    NSLog(@"Age from text field::%i", age);

    AppDelegate *appDelegate = 
        (AppDelegate *)[UIApplication sharedApplication].delegate;

    Person *myPerson = (Person *)[appDelegate person];
    NSLog(@"Age before setting: %i", [myPerson age]);
    [myPerson setAge:age];
    NSLog(@"Age after setting: %i", [myPerson age]);

    [textAge release];
}
...

The output of the above NSLogs are:

[Session started at 2010-05-04 18:29:22 +0100.]
2010-05-04 18:29:28.260 AccuTax[16235:207] Age in text field:25
2010-05-04 18:29:28.262 AccuTax[16235:207] Age before setting: 0
2010-05-04 18:29:28.263 AccuTax[16235:207] Age after setting: 0

Any ideas why 'age' isn't being stored? I'm relatively new to Obj-C so please forgive me if I'm missing something very simple!

Looks like you never actually created an instance of Person -- in AccuTaxAppDelegate add an init method which contains the line

person = [[Person alloc] init];

otherwise person is nil;