NSString --> NSArray

NSArray *arr = [str componentsSeparatedByString:@","];

NSArray --> NSString

NSString *str = [arr componentsJoinedByString:@","];

NSString --> NSData

NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding]; 

NSData --> NSString

NSString *str = [[NSString alloc] initWithData:data  encoding:NSUTF8StringEncoding]; 

NSDate --> NSString

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSString *str = [dateFormatter stringFromDate:date];

NSString --> NSDate

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSDate *date = [dateFormatter dateFromString:str];

NSString --> NSDictionary

NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];

NSDictionary --> NSString

NSData *data = [NSJSONSerialization dataWithJSONObject:dic options:NSJSONWritingPrettyPrinted error:nil];
NSString*str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

NSArray --> NSData

NSData *data = [NSKeyedArchiver archivedDataWithRootObject:arr];

NSData --> NSArray

NSArray *arr = [NSKeyedUnarchiver unarchiveObjectWithData:data];

NSDictionary --> NSData

NSMutableData *data = [[NSMutableData alloc] init];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data]; 
[archiver encodeObject:dic forKey:@"Some Key Value"]; 
[archiver finishEncoding];

NSData --> NSDictionary

NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data]; 
NSDictionary *dic = [unarchiver decodeObjectForKey:@"Some Key Value"]; 
[unarchiver finishDecoding];

UIImage --> NSData

+ (NSData *)imageToData:(UIImage *)image CompressionNum:(int)num
{
    return UIImageJPEGRepresentation(image, num)?:UIImagePNGRepresentation(image);
}