Managing Global Application Settings Using NSUserDefaults | iOS Programmer Guide

To achieve this kinds of scenario, we can use NSUserDefaults. From anywhere in your code, you can set a value for a key :

int userAge = 21; // Just an example

NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];

if (standardUserDefaults) {
    [standardUserDefaults setObject:[NSNumber numberWithInt:userAge] forKey:@"age"];
    [standardUserDefaults synchronize];
}

And get it back from any other place :

NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
NSNumber *age = nil;

if (standardUserDefaults) 
    age = [standardUserDefaults objectForKey:@"age"];

userAge = [age intValue]

You can also set an initial value :

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSDictionary *appDefaults = [NSDictionary
    dictionaryWithObject:[NSNumber numberWithInt:13] forKey:@"age"];

[defaults registerDefaults:appDefaults];

You can write the value into NSUserDefault like the following:

[[NSUserDefaults standardUserDefaults] setValue:[myTextField stringValue] forKey:@"Person"];

And read it later like the following:

[myTextField setStringValue:[[NSUserDefaults standardUserDefaults] stringForKey:@"Person"];

Also, if you have complex data, you may want to create a wrapper class with setters and getters.