Saving NSdictionary in NSUserDefaults - ios

Question

I tried to save an NSDictionary in NSUSerDefaults, but I get the following error:
Attempt to insert non-property value
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
if(defaults) {
[defaults setBool: YES forKey: #"disableGetStarted"];
[defaults setObject: [json mutableCopy] forKey: #"user"];
[defaults synchronize];
NSLog(#"defaults %#", [defaults objectForKey: #"user"]);
}
Where json is an NSDictionary.
What can I do?

Answer 1

json may be a dictionary but all of the contents of the dictionary must be legal values to be stored in user defaults. All must be instances of: NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary.

Answer 2

If you only store standard objects inside the dictionary like NSData, NSString, NSNumber, NSDate, NSArray, NSDictionary or a combination of them you don't have to do anything special.
However, if you have instances of custom objects in it (i.e. classes that you've created) you first need to convert it into a compatible type (e.g. NSData). You can do this using the code below:
NSData* data=[NSKeyedArchiver archivedDataWithRootObject:json];
[NSUserDefaults standardUserDefaults] setObject:data forKey:#"user"]
For this method to work, you ned to implement these 2 methods in the custom classes you are trying to save:
- (id)initWithCoder:(NSCoder*)coder
- (void)encodeWithCoder:(NSCoder*)coder;
To get the dictionary back from NSUserDefaults (decode) you can use:
NSData* data = [[NSUserDefaults standardUserDefaults] objectForKey:#"user"];
NSDictionary* json = [NSKeyedUnarchiver unarchiveObjectWithData:data];
EDIT
To check if your json object contains any [NSNull null] values, add this piece of code before you are making your insert into NSUserDefaults
for (id val in [json allValues])
{
if ([val isKindOfClass:[NSNull class]])
{
NSLog(#"This bad! NSNull should not be in the dictionary");
break;
}
}
If you get any This is bad... messages in the console, then you have 2 choices.
1. Use the archiving/unarchiving method I described above
2. Replace the NSNull objects from the dictionary with other values (e.g. empty strings) if this does not break your code.

Answer 3

One or more of the objects in your dictionary are not NSString, NSArray, NSDictionary, NSDate or NSData, the only objects that may be present. This code may help, it gives you more details why your dictionary is not valid:
- (BOOL)isValidPropertyList:(id)object {
//
// Check if `object` is a valid property list.
//
// # Return Value
// `YES` if the receiver is a valid property list, `NO` otherwise.
//
// # Discussion
// Intended to be called on NSArray and NSDictionary object to verify if the
// receiver is a valid property list. Will emit a description of any
// detected error.
//
NSData *xmlData;
NSString *error;
xmlData=[NSPropertyListSerialization
dataFromPropertyList:object
format:NSPropertyListXMLFormat_v1_0
errorDescription:&error
];
if(xmlData)
{
return YES;
}
else
{
NSLog(#"Tested object is not a valid property list: %#",error);
}
return NO;
}

Answer 4

NSDictionary *dict = [[NSDictionary alloc] init];
dict = json;
[NSUserDefaults standardDefaults] setObject:dict forKey:#"user"];
NSUserDefaults doesn't distinguish between mutable and immutable objects, so when you get it back it'll be immutable. So if you make a mutable dictionary by chance ->
[[NSUserDefaults standardDefaults] setObject:dict forKey:#"user"] mutableCopy];
All objects of the dictionary json must be instances of: NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary.