How to manage data in a iOS app - objective-c

Question

I'm developing an app where I have some data. It would be some strings I want to use.
The issue is I would like to initialize with the data of a file. something like:
#property (strong, nonatomic) Cow *cow;
_cow = [[Cow alloc] init (NSString *) #"Some string"];
I have the proper constructor for cow that accepts an string .
What I want is the way I can initialize severals cows with different strings and repeat some values if I want.
I was thinking in a text file where I have all the strings, and just pick those I want.
Another possibility is a db like SQlite.

Answer 1

Reading your comments to other answers, it seems that you are interested in an object graph persistence mechanism for your application. The answer given by #Greg - object graph serialization - is excellent. In the default case, you'd be reading your entire object graph into memory, which may or may not be what you want. (There are ways of dealing with that too.) You asked about how to choose data you want. In the case where your Cow's are in memory, you can find your Cow of choice in a lot of ways. For example:
#import <Foundation/Foundation.h>
#interface Cow : NSObject
#property (nonatomic,copy) NSString *color;
#end
#implementation Cow
#end
int main(int argc, char *argv[]) {
#autoreleasepool {
Cow *brownCow = [Cow new];
brownCow.color = #"brown";
Cow *whiteCow = [Cow new];
whiteCow.color = #"white";
NSArray *cows = #[brownCow,whiteCow];
NSUInteger cowIndex = [cows indexOfObjectPassingTest:^BOOL(Cow *obj, NSUInteger idx, BOOL *stop) {
return [[obj color] isEqualToString:#"brown"];
}];
if( cowIndex != NSNotFound )
NSLog(#"Your brown cow is: %#",cows[cowIndex]);
else
NSLog(#"No brown cow");
}
}
But there are other object persistence frameworks that you may consider. For example, Core Data is commonly used. sqlite3 is another possibility, which when used with an object-oriented abstraction layer like FMDB is another good choice.
The answer boils down to your requirements. How many Cow objects might there be? What are the performance requirements? And so on.

Answer 2

You can make your object Cow conform to a NSCoding protocol:
//Cow.h file
#interface Cow : NSObject <NSCoding>
#property(nonatomic, copy) NSString *someString;
#end
//Cow.m
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super init];
if (self) {
_someString = [aDecoder decodeObjectForKey:#"someString"];
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)aCoder
{
[aCoder encodeObject:self.someString forKey:#"someString"];
}
And after that you can save it to a file (you can create array of Cow objects and save it to a file):
NSrray *data = #[cow1, cow2, cow3];
[NSKeyedArchiver archiveRootObject:data toFile:[self pathToFile]];
And you can read it like that:
NSFileManager* fileManager = [NSFileManager defaultManager];
if ([fileManager fileExistsAtPath:[self pathToData]])
{
NSData *data = [NSData dataWithContentsOfFile:[self pathToData]];
NSMutableArray *dataArray = [NSKeyedUnarchiver unarchiveObjectWithData:data];
// dataArray -> array with your data
}
Hopefully I understood your question.
//EDITED
Get file to path:
-(NSString*)pathToData
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *filePath = [documentsDirectory stringByAppendingPathComponent:#"MyData"];
NSFileManager* fileManager = [NSFileManager defaultManager];
if (![fileManager fileExistsAtPath:filePath])
{
[fileManager createDirectoryAtPath:filePath withIntermediateDirectories:NO attributes:nil error:nil];
}
return [filePath stringByAppendingPathComponent:#"mydata.plist"];
}
Save and remove data:
-(BOOL)save
{
NSMutableArray *data = [self cachedDataFromFile];
if (!data)
{
NSLog(#"data = nil");
data = [NSMutableArray arrayWithArray:#[self]];
}
else
[data addObject:self];
return [NSKeyedArchiver archiveRootObject:data toFile:[self pathToData]];
}
-(void)removeFromFile
{
NSMutableArray *data = [self cachedDataFromFile];
if (!data)
return;
else
{
[data removeObject:self];
[NSKeyedArchiver archiveRootObject:data toFile:[self pathToData]];
}
}
-(NSMutableArray*)cachedDataFromFile
{
NSFileManager* fileManager = [NSFileManager defaultManager];
if ([fileManager fileExistsAtPath:[self pathToData]])
{
NSData *data = [NSData dataWithContentsOfFile:[self pathToData]];
NSMutableArray *dataArray = [NSKeyedUnarchiver unarchiveObjectWithData:data];
return dataArray;
}
return nil;
}
Let me know is it work for you.