iOS get day difference by NSDateComponents

+ (NSInteger) daysdifference:(NSString*)start end:(NSString*)end
{
    //start = @"2013-01-26";
    //end = @"2013-02-09";
    NSDateFormatter *df = [[NSDateFormatter alloc]init];
    [df setDateFormat:@"yyyy/MM/dd"];
    NSDate *startDate = [df dateFromString:start];
    NSDate *endDate = [df dateFromString:end];
    
    NSCalendar *gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *components = [gregorianCalendar components:NSDayCalendarUnit
                                                        fromDate:startDate
                                                          toDate:endDate
                                                         options:0];
    return components.day;
}