Saving NSMutableArray to NSUserDefaults - ios

Question

I have an NSMutableArray inside of my AppDelegate, and I'm attempting to save it to NSUserDefaults. The NSMutableArray (strainsfinal) contains a list of favorited items. I want this list to save, and be present even if the app is shut down, and then restarted. Does anyone know why my code isn't working (not saving my data)? See below:
AppDelegate.m
-(void)updateStrains:(NSDictionary *)item
{
NSUserDefaults *currentDefaults = [NSUserDefaults standardUserDefaults];
NSData *dataSave = [currentDefaults objectForKey:#"strains"];
if (strainsfinal != nil)
{
NSArray *oldSavedArray = [NSKeyedUnarchiver unarchiveObjectWithData:dataSave];
if (oldSavedArray != nil)
strainsfinal = [[NSMutableArray alloc] initWithArray:oldSavedArray];
else
strainsfinal = [[NSMutableArray alloc] init];
}
}
EDIT: Appdelegate.m So I've changed my above method to the method below (and I thought it should work), but the app crashes, saying: "Terminating app due to uncaught exception 'NSInvalidArguementException', reason: 'NSConcreteAttributedString initwithString: nil 'value'.
What am I missing?!
-(void)updateStrains:(NSDictionary *)item {
NSData *dataSave = [NSKeyedArchiver archivedDataWithRootObject:strainsfinal];
[[NSUserDefaults standardUserDefaults] setObject:dataSave forKey:#"strains"];
NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
[nc postNotificationName:#"arrayupdated" object:self userInfo:nil];
NSLog(#"updated strains %#",strainsfinal);
}

Answer 1

You must add
[currentDefaults synchronize];
each time after you save something to userDefaults;
But for such kind of data is better to use .plist files.
Check documentation for more info.
EDITED Code:
-(void)updateStrains:(NSDictionary *)item {
NSData *dataSave = [NSKeyedArchiver archivedDataWithRootObject:item[#"strainsfinal"]];
[[NSUserDefaults standardUserDefaults] setObject:dataSave forKey:#"strains"];
// NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
// [nc postNotificationName:#"arrayupdated" object:self userInfo:nil];
NSLog(#"updated strains %#",strainsfinal);
[[NSUserDefaults standardUserDefaults] synchronize]; // this will save you UserDefaults
}

Answer 2

use following method :
NSUserDefaults *userDef = [NSUserDefaults standardUserDefaults];
[userDef setObject:array1 forKey:#"DataArra1"];
[userDef setObject:array2 forKey:#"DataArr2"];
[userDef synchronize];
To retrieve the information:
NSUserDefaults *userDef = [NSUserDefaults standardUserDefaults];
NSArray *arrayText2 = [userDef objectForKey:#"DataArra1"];
NSArray *arrayText1 = [userDef objectForKey:#"DataArr2"];

Answer 3

You should archive NSArray before saving.
[[NSUserDefaults standardUserDefaults]
setObject:[NSKeyedArchiver archivedDataWithRootObject:yourArray]
forKey:#"yourArray"];
and unarchive when getting from NSUserDefaults.
NSData *data = [currentDefaults objectForKey:#"yourArray"];
if (data != nil)
{
NSArray *savedArray = [NSKeyedUnarchiver unarchiveObjectWithData:data];
}