Save large NSDictionary to disk iOS - ios

Question

My application is designed to view the catalog with products. All data received from the server (xml) are parsed in NSDictionary. So NSDictionary contains about 5000 items. Reading a dictionary using NSKeyedUnarchiver takes 24 seconds. It is unacceptable.
I don't need forward and backward compatible, because after app updating catalog will be downloaded again and old data will be deleted.
My dictionary isn't property list, so writeToFile isn't working.
NSArchiever(NSUnarchiever) would be a great solution to the problem, but it replaced by NSKeyedArchiver.
Any ideas? Maybe I should use CoreData but I don't know anything about it.
Thanks

Answer 1

Have you tried saving it as a JSON formatted file? NSJSONSerialization would help you go back and forth between file data and a NSDictionary. It was added in iOS5.
https://developer.apple.com/library/ios/documentation/Foundation/Reference/NSJSONSerialization_Class/Reference/Reference.html
Let me know if it performs well enough for you.

Answer 2

My solution is to use custom serialization. In the end, all data is presented as property list. All my custom classes that should be serialized support protocol PropertyListCoder (like NSCoder):
#protocol PropertyListCoder
- (id)encodeToPropertyListObject;
- (id)initWithPropertyListObject:(id)object;
#end
For example, serialization for class Product:
#interface Product : NamedObject <NSCoding, PropertyListCoder> {
}
#property (nonatomic, readwrite) uint mId;
#property (nonatomic, retain) NSString *mDesc;
#property (nonatomic, retain) NSString *mIcon;
#property (nonatomic, retain) NSString *mCode;
#property (nonatomic, readwrite) uint mSort;
#property (nonatomic, retain) NSMutableArray *mArrOfText;
#property (nonatomic, readonly) NSMutableArray *mProperties;
#property (nonatomic, retain) NSString *mImage;
#property (nonatomic, readwrite) float mPrice;
#property (nonatomic, readwrite) float mDiscPrice;
#end
And here are methods of the protocol:
- (id)encodeToPropertyListObject {
id superPropList = [super encodeToPropertyListObject];
NSNumber* idNumber = [[NSNumber alloc] initWithInt:mId];
NSNumber* sortNumber = [[NSNumber alloc] initWithInt:mSort];
NSMutableArray* arrOfTextPropList = [[NSMutableArray alloc] init];
for (NSAttString* str in self.mArrOfText) {
[arrOfTextPropList addObject:[str encodeToPropertyListObject]];
}
NSMutableArray* propPropList = [[NSMutableArray alloc] init];
for (Property* prop in self.mProperties) {
[propPropList addObject:[prop encodeToPropertyListObject]];
}
NSNumber* priceNumber = [[NSNumber alloc] initWithInt:mPrice];
NSNumber* discPriceNumber = [[NSNumber alloc] initWithInt:mDiscPrice];
NSArray* res = [NSArray arrayWithObjects:superPropList, idNumber, [Utility notNilStringWithString:mDesc], [Utility notNilStringWithString:mIcon], [Utility notNilStringWithString:mCode], sortNumber, arrOfTextPropList, propPropList, [Utility notNilStringWithString:mImage], priceNumber, discPriceNumber, nil];
[idNumber release];
[sortNumber release];
[arrOfTextPropList release];
[propPropList release];
[priceNumber release];
[discPriceNumber release];
return res;
}
- (id)initWithPropertyListObject:(id)object {
NSArray* arr = (NSArray*)object;
self = [super initWithPropertyListObject:[arr objectAtIndex:0]];
if (self) {
mId = [[arr objectAtIndex:1] intValue];
mDesc = [[arr objectAtIndex:2] retain];
mIcon = [[arr objectAtIndex:3] retain];
mCode = [[arr objectAtIndex:4] retain];
mSort = [[arr objectAtIndex:5] intValue];
mArrOfText = [[NSMutableArray alloc] init];
mProperties = [[NSMutableArray alloc] init];
for (id subObj in (NSArray*)[arr objectAtIndex:6]) {
NSAttString* str = [[NSAttString alloc] initWithPropertyListObject:subObj];
[mArrOfText addObject:str];
[str release];
}
for (id subObj in (NSArray*)[arr objectAtIndex:7]) {
Property* prop = [[Property alloc] initWithPropertyListObject:subObj];
[mProperties addObject:prop];
[prop release];
}
mImage = [[arr objectAtIndex:8] retain];
mPrice = [[arr objectAtIndex:9] floatValue];
mDiscPrice = [[arr objectAtIndex:10] floatValue];
}
return self;
}
Root object could be NSDictionary or NSArray. Then for read / write I use NSPropertyListSerialization with binary format.
And now reading the dictionary takes 3.5 seconds!