iPhone, I need to reuse an NSArray which has constant values in different views, how?

Question

I have the following array.

    NSArray *arrayDisplay = [[NSArray alloc] initWithObjects:@"Daily", 
        @"Weekly", @"Monthly", nil];

I need to use it in two views, I'm concerned that I may make changes and forget to change the other in the future. So I'd like to declare it once and reuse it.

How should I do this?

Answer 1

You can keep it as a property in a common object such as the application delegate.

Assuming its nonatomic,retain type property then access it like:

myAppDelegate *del = [[UIApplication sharedApplication] delegate];
del.arrayDisplay = [NSArray arrayWithObjects:@"Daily",@"Weekly", @"Monthly", nil];

Although if you plan on changing it you might want an NSMutableArray.

Answer 2

You could save the array as a plist in your project and load it in each place where it's needed with

NSArray *arrayDisplay = [[NSArray alloc] initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"myArrayName" ofType:@"plist"]];

This will work as long as you do not need to change the values in both place while the program is actually running.

Answer 3

If your application is simple, consider the Singleton model where the data you are accessing are accessible through the global instance of the singleton. link text

Answer 4

Consider writing a class method or even a C function that lazily creates the array. For example, here's a class method that does what you want:

+ (NSArray *)frequencyChoices
{
    static NSArray *choices;

    if (choices == nil)
    {
        choices = [[NSArray alloc] initWithObjects:
                   @"Daily", @"Weekly", @"Monthly", nil]; 
    }

    return choices;
}

Writing the same functionality as a C function makes it even more general:

NSArray *frequencyChoices(void)
{
    static NSArray *choices;

    if (choices == nil)
    {
        choices = [[NSArray alloc] initWithObjects:
                   @"Daily", @"Weekly", @"Monthly", nil]; 
    }

    return choices;
}

The advantage of a class method though, is that you could override it in a subclass if that might ever prove handy.

Answer 5

Rather than using a Singleton approach, consider determining which object in your app's object hierarchy should own this array, and then pass that reference down to where it's needed (see: dependency injection).

Answer 6

If you don't mind global variables, you can instantiate them at load time:

@interface FooClass : ... {
  ...
}

static NSArray * FooClass_timescale;

@end


@implementation FooClass

+(void)load {
  FooClass_timescale = [[NSArray alloc] initWithObjects:@"Daily", @"Weekly", @"Monthly", nil]; 
}

@end

I prefer doing this when there are a pile of things I want to instantiate (e.g. colours for a theme/skin/brand/whatever), since it's shorter than writing a function to return them. Of course, it's possible to accidentally modify the global variable, but I've never managed this (usually I just forget to retain).