Question

I’d like to save an NSMutableDictionary object in NSUserDefaults. The key type in NSMutableDictionary is NSString, the value type is NSArray, which contains a list of object which implements NSCoding. Per document, NSString and NSArray both are conform to NSCoding.

I am getting this error:

[NSUserDefaults setObject: forKey:]: Attempt to insert non-property value…. of class NSCFDictionary.

Answer 1

I found out one alternative, before save, I encode the root object (NSArray object) using NSKeyedArchiver, which ends with NSData. Then use UserDefaults save the NSData.

When I need the data, I read out the NSData, and use NSKeyedUnarchiver to convert NSData back to the object.

It is a little cumbersome, because i need to convert to/from NSData everytime, but it just works.

Here is one example per request:

Save:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; NSMutableArray *arr = ... ; // set value NSData *data = [NSKeyedArchiver archivedDataWithRootObject:arr]; [defaults setObject:data forKey:@'theKey']; [defaults synchronize]; 

Load:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; NSData *data = [defaults objectForKey:@'theKey']; NSArray *arr = [NSKeyedUnarchiver unarchiveObjectWithData:data]; 

The element in the array implements

@interface CommentItem : NSObject<NSCoding> {     NSString *value; } 

Then in the implementation of CommentItem, provides two methods:

-(void)encodeWithCoder:(NSCoder *)encoder {     [encoder encodeObject:value forKey:@'Value']; }  -(id)initWithCoder:(NSCoder *)decoder {     self.value = [decoder decodeObjectForKey:@'Value'];     return self; } 

Anyone has better solution?

Thanks everyone.