Pass a variable between lots of UIVIewControllers

Question

In my iPhone app, there is a setup assistant which helps users to input a lot of data. It\'s basically a UINavigationController with lots of UIViewControllers in it. Now, at

Answer 1

A simple yet reusable and extensible way to solve this problem is using a singleton.

Declare a new class named SetupConfig, for example.

Your SetupConfig.h should then look as follows:

@interface SetupConfig : NSObject {
    NSString *_myString;
}

@property (retain) NSString *myString;

+ (id)sharedSetupConfig;

@end

And the corresponding SetupConfig.m:

#import "SetupConfig.h"

SetupConfig *g_sharedSetupConfig = nil;

@implementation SetupConfig

@synthesize myString = _myString;

+ (id)sharedSetupConfig {
    if (!g_sharedSetupConfig) {
        g_sharedSetupConfig = [[SetupConfig alloc] init];
    }
}

@end

Now, in the view controller implementation you want to access myString from:

@import "MyViewController.h"
@import "SetupConfig.h"

@implementation MyViewController

- (void)methodDoingSomethingWithSingletonString
{
    NSString *myString = [[SetupConfig sharedSetupConfig] myString];
} 

@end

The singleton approach comes with a number of advantages over using a global C variable. First of all you do not have to re-declare your global variables over and over. What is more, your "global" variables are encapsulated in a class. Synthesizing property getters/setters is a nice way to abstract the actual variable away from the rest of your code. Finally, this implementation may be integrated into unit tests easily.