How to use NSUserDefaults to save state of switch?

If you have an application that should save for example state of a switch and you don’t want use database for that small request you can simply add instance of NSUserDefaults class in your implementation. It is easy job, see below;

- (IBAction) saveState {
 
NSString *value = @"ON";
NSUserDefaults *userPreferences = [NSUserDefaults standardUserDefaults];
if(!switch.on){
value = @"OFF";
[userPreferences setObject:value forKey:@"stateOfSwitch"];
}
[userPreferences setObject:value forKey:@"stateOfSwitch"];
 
}

This is part of code that loads value in a NSString *value for key stateOfSwitch. When you start your application again and view finisheds with loading button will be in lefted state.

- (void)viewWillAppear:(BOOL)animated {
 
NSString *_value= [[NSUserDefaults standardUserDefaults] stringForKey:@"stateOfSwitch"];
 
if([_value compare:@"ON"] == NSOrderedSame){
switch.on = YES;
}
else {
switch.on = NO;
}
[super viewWillAppear:animated];
}

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

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:).