Use NSUserDefault

If you have an application that should save any values or objects or preferences (like :how to access preference from your iOS Applications)  for example state of a switch, state of background and you don’t want use database for that small request you can simply add instance of NSUserDefaults class in your implementation.

Information About NSUserDefaults:
With the NSUserDefaults class, you can save settings and properties related to application or user data. For example, you could save a profile image set by the user or a default color scheme for the application. The objects will be saved in what is known as the iOS “defaults system”. The iOS defaults system is available throughout all of the code in your app, and any data saved to the defaults system will persist through application sessions. This means that even if the user closes your application or reboots their phone, the saved data will still be available the next time they open the app!

Main Points:

1. This is Singleton Class.
2. NSUserDefaults class gives us an opportunity to save values without database use.
3. use KVC model for saving and loading values.
4. Key-value coding (KVC) defines generic property accessor methods—valueForKey: and setValue:forKey:—which identify properties with string-based keys.
   

KVC Info:
KVC is not meant as a general alternative to using accessor methods—it is for use by code that has no other option, because the code cannot know the names of the relevant properties at compile time. Key-value coding and the dot syntax are orthogonal technologies. You can use KVC whether or not you use the dot syntax, and you can use the dot syntax whether or not you use KVC. Both, though, make use of a “dot syntax”.
In the case of KVC, the syntax is used to delimit elements in a key path. It is important to remember that when you access a property using the dot syntax, you invoke the receiver ’s standard accessor methods (as a corollary, to emphasize, the dot syntax does not result in invocation of KVC methods valueForKey: or setValue:forKey:).

With NSUserDefaults you can save objects from the following class types:

• NSData
• NSString
• NSNumber
• NSDate
• NSArray
• NSDictionary

It is easy job, see below:


Code to save data into NSUserDefaults:

======================Objective C Code========================
NSString *dataString = @"background.png";
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
if(standardUserDefaults)
{
        [standardUserDefaults setObject: dataString forKey:@"BackgroundImage_Key"];
         [standardUserDefaults synchronize];
}
=============================================================

There are different accessor methods depending on the type of variable you want to retrieve.

• arrayForKey
• boolForKey
• dataForKey
• dictionaryForKey
• floatForKey
• integerForKey
• objectForKey
• stringArrayForKey
• stringForKey
• valueForKey

Code to Retrive data into NSUserDefaults:
======================Objective C Code========================

NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
NSString *dataValue = @"";
if(standardUserDefaults)
 {
     dataValue = [standardUserDefaults objectForKey:@"BackgroundImage_Key"] ;
     NSLog(@"Output = Data Value ==>%@ ",dataValue);
}

OUTPUT:
             Output = Data Value ==> background.png.
 =============================================================

 References:

• http://mobile.tutsplus.com/tutorials/iphone/nsuserdefaults_iphone-sdk/
• http://inchoo.net/mobile-development/iphone-development/how-to-use-nsuserdefaults-to-save-state-of-switch/
• http://zcentric.com/2008/08/20/using_nsuserdefaults/