I am trying to save a NSDictionary with array values to NSUserDefaults but am having some strange trouble.
My NSDictionary has NSStrings for keys and each value is a NSArray of NSNumbers. When I print the dictionary out, everything is fine. I write this dictionary to NSUserDefaults and if I read it back out right away, everything seams fine. Using this everything seams just fine:
[[NSUserDefaults standardUserDefaults] setObject:self.selectedOptionPositions
forKey:PREF_OPTIONS_KEY];
[[NSUserDefaults standardUserDefaults] synchronize];
//THIS PRINT EVERYTHING OUT EXACTLY AS IT SHOULD!
NSLog(#"read after write: %#", [[NSUserDefaults standardUserDefaults]
objectForKey:PREF_OPTIONS_KEY]);
The problem comes when I create a new instance of the class that handles this. When I make a new instance of the class and in the init method check the NSDictionary like so:
NSLog(#"read initial: %#", [[NSUserDefaults standardUserDefaults]
objectForKey:PREF_OPTIONS_KEY]);
When I print that logging, the NSDictionary contains all of the keys but all of the values are now empty! All newly added keys exist after recreating the class, but no values persist.
What could be wrong here? There are no warnings or errors in the console.
Try this:
You can use NSKeyedArchiver to write out your dictionary to an NSData, which you can store among the preferences.
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:self.selectedOptionPositions];
[[NSUserDefaults standardUserDefaults] setObject:data forKey:PREF_OPTIONS_KEY];
For retrieving data:
NSData *dictionaryData = [defaults objectForKey:PREF_OPTIONS_KEY];
NSDictionary *dictionary = [NSKeyedUnarchiver unarchiveObjectWithData:dictionaryData];
As in the iOS Developer Documentation for NSKeyedArchiver it says that:
NSKeyedArchiver, a concrete subclass of NSCoder, provides a way to
encode objects (and scalar values) into an architecture-independent
format that can be stored in a file. When you archive a set of
objects, the class information and instance variables for each object
are written to the archive. NSKeyedArchiver’s companion class,
NSKeyedUnarchiver, decodes the data in an archive and creates a set of
objects equivalent to the original set.
Related
I am trying to save an array of objects into an NSUserDefault without success. When I log out the array before the attempt it is full of object. However, when I try to log out the NSUserDefault it is NULL. Can anyone see what I might be doing wrong? Thanks for any suggestions:
Items *myItems = [mutableFetchedObjects mutableCopy];
NSLog(#"my Items%#",myItems);//LOGS OUT LONG LIST OF ITEMS
NSUserDefaults *currentDefaults = [NSUserDefaults standardUserDefaults];
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:myItems];
[currentDefaults setObject:data forKey:#"myItems"];
[currentDefaults synchronize];
Items *myRetrievedItems = [[[NSUserDefaults standardUserDefaults] arrayForKey:#"myItems"] mutableCopy];
NSLog(#"my Retrieved Items%#",myRetrievedItems); //LOGS OUT AS NULL
As the other answers mentioned, it is because your array is not complying to the NSDictionary types (string, binary, bool, etc). Your members of array is of custom types therefore it cannot be saved. What you need to do is convert your array to binary first and then save it.
You have to unarchive your data first at the time of retrieving back. You are directly accessing the data. This won't work. You can do it the similar way you are archiving the data
NSData *dataObj = [currentDefaults objectForKey:#"myItems"];
Items *myRetrievedItems = [NSKeyedUnarchiver unarchiveObjectWithData:dataObj];
For more reference, you can consider this answer.
Hope this helps.
Thanks!
Your access value method is wrong.
You can get the array in following code:
Items *myRetrievedItems = [[[NSUserDefaults standardUserDefaults] objectForKey:#"myItems"] mutableCopy];
I've got an app where I use a JSON based API. As part of JSON, often values are set to "null". This may be common:
{"data":["one","two","three"],"name":null,otherstuff:10}
Recently I've tried to store a misc NSDictionary hierarchy, converted from a JSON object, in NSUserDefaults. Unfortunately it causes an exception if there is null data, converted in IOS to [NSNull null]. Apparently that can't be saved in prefs.
I was wondering if anyone has worked around this before? I tried to add some logic to remove all null values from the JSON first, with limited success, but it seems inappropriate to have to modify the data before storing it. Is there a better way to handle this?
You can first convert your NSDictionary to NSData, then safely store in NSUserDefaults (since NSNull conforms to NSCoding).
//archive
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:dictionary];
[[NSUserDefaults standardUserDefaults] setObject:data forKey:#"key"];
//unarchive
NSData *newData = [[NSUserDefaults standardUserDefaults] objectForKey:#"key"];
NSDictionary *newDict = [NSKeyedUnarchiver unarchiveObjectWithData:newData];
Edit: Original data object was being referenced instead of newData object.
I've tried some recursive solutions but they tend to be complicated and don't handle mixed type content well. At the simplest level here is a flat example that works well if you have a predictable, flat response to clean.
NSMutableDictionary *dictMutable = [dict mutableCopy];
[dictMutable removeObjectsForKeys:[dict allKeysForObject:[NSNull null]]];
I've got an app where I use a JSON based API. As part of JSON, often values are set to "null". This may be common:
{"data":["one","two","three"],"name":null,otherstuff:10}
Recently I've tried to store a misc NSDictionary hierarchy, converted from a JSON object, in NSUserDefaults. Unfortunately it causes an exception if there is null data, converted in IOS to [NSNull null]. Apparently that can't be saved in prefs.
I was wondering if anyone has worked around this before? I tried to add some logic to remove all null values from the JSON first, with limited success, but it seems inappropriate to have to modify the data before storing it. Is there a better way to handle this?
You can first convert your NSDictionary to NSData, then safely store in NSUserDefaults (since NSNull conforms to NSCoding).
//archive
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:dictionary];
[[NSUserDefaults standardUserDefaults] setObject:data forKey:#"key"];
//unarchive
NSData *newData = [[NSUserDefaults standardUserDefaults] objectForKey:#"key"];
NSDictionary *newDict = [NSKeyedUnarchiver unarchiveObjectWithData:newData];
Edit: Original data object was being referenced instead of newData object.
I've tried some recursive solutions but they tend to be complicated and don't handle mixed type content well. At the simplest level here is a flat example that works well if you have a predictable, flat response to clean.
NSMutableDictionary *dictMutable = [dict mutableCopy];
[dictMutable removeObjectsForKeys:[dict allKeysForObject:[NSNull null]]];
I'm thingking of create a base class where every change made is immediately saved to NSUserDefaults (only KVO compilant parts of course), and automatically loads whenever that type of object is instantiated (a really basic, reusable user data store).
I have no intention to provide a "list of keys"-like constant to every subclass of this object, so I'm hoping that there is an automatic way to observe every property of an object.
Any ideas how to do this? With merely public API of course.
If you have a set of properties for an object, you can save them to a dictionary in NSUserDefaults. To save each property every time it is set you can create custom setter methods for each property using this:
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
if ([defaults objectForKey:#"yourKey"] == nil) {
NSDictionary *dict = [NSDictionary dictionaryWithObject:#"yourObject" forKey:#"keyForYourObject"];
// Add stuff to the dictionary
[defaults setObject:dict forKey:#"yourKey"];
}else{
NSDictionary *dict = [defaults objectForKey:#"yourKey"];
// Add stuff to the dictionary
[defaults setObject:dict forKey:#"yourKey"];
}
This will give you a single dictionary stored in UserDefaults with all the properties. Then to get the list of keys use the standart method:
NSDictionary *dict = [[NSUserDefaults standardUserDefaults] objectForKey:#"yourKey"];
NSArray *keys = [dict allKeys];
I try to save my object to NSUserDefaults. But when I call this method again it is not have any info about previous operation.
There is my method below:
- (void)addToCart {
if([[NSUserDefaults standardUserDefaults] objectForKey:kCart]) {
NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
NSMutableArray *products = [[NSMutableArray alloc] initWithArray:[prefs objectForKey:kCart]];
[products addObject:self.product];
[prefs setObject:products forKey:kCart];
[prefs synchronize];
[products release];
}
else {
//Saving...
NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
[prefs setObject:[NSArray arrayWithObjects:self.product, nil] forKey:kCart];
[prefs synchronize];
}
}
I need to save a collection with a products to NSUserDefault. I wrap my object to NSArray and save it but it doesn't work.
Everything put into NSUserDefaults must be a valid property list object (NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary). All collection elements must themselves also be property list objects.
In order to save non-PL objects into NSUserDefaults, you must first convert the object into a PL object. The most generic way to do this is by serializing it to NSData.
Serializing to NSData is handled with NSKeyedArchiver. See Storing NSColor in User Defaults for the canonical example of this. (That document is very old and still references NSArchiver which will work fine for this problem, but NSKeyedArchiver is now the preferred serializer.)
In order to archive using NSKeyedArchiver, your object must conform to NSCoding as noted by #harakiri.
You need to conform to the <NSCoding> protocol and implement -initWithCoder: and -encodeWithCoder: in your custom object.
See: https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Protocols/NSCoding_Protocol/Reference/Reference.html