Monkey-Patching iOS with Objective-C Categories Part I: Simple Extensions and Overrides

AClassACategoryImplementation.h

#import <Foundation/Foundation.h>

@interface AClass (ACategory)

@end

AClassACategoryImplementation.m

#import "AClass+ACategory.h"

@implementation AClass (ACategory)

@end

EntryCell.m

#import "NSDate+Formatting.h"

@implementation EntryCell

...

@end

Extensions.h

#import "NSDate+Formatting.h"
#import "UIFonts+MyFonts.h"
#import "UIViewController+Tourbot.h"

gistfile1.sh

3 minutes ago

NSDateFormatting.h

#import <Foundation/Foundation.h>

@interface NSDate (Formatting)

- (NSString*) timeAgoInWords;

@end

NSDateFormatting.m

#import "NSDate+Formatting.h"

@implementation NSDate (Formatting)

- (NSString *)timeAgoInWords {
  double seconds = [self timeIntervalSinceNow];
  seconds = seconds * -1;

  if(seconds < 1) {
    return @"now";
  } else if (seconds < 60) {
    return @"less than a minute ago";
  } else {
    NSUInteger difference = 0;
    BOOL pluralize = NO;
    NSString* unit = @"";
    
    if (seconds < 3600) {
      difference = round(seconds / 60);
      unit = @"minute";
    } else if (seconds < 86400) {
      difference = round(seconds / 3600);
      unit = @"hour";
    } else if (seconds < 604800) {
      difference = round(seconds / 86400);
      unit = @"day";
    } else if (seconds < 2592000) {
      difference = round(seconds / 604800);
      unit = @"week";
    } else if (seconds < 31557600) {
      difference = round(seconds / 2592000);
      unit = @"month";
    } else {
      difference = round(seconds / 2592000);
      unit = @"year";
    }
    
    if (difference > 1) {
      pluralize = YES;
    }
    
    return [NSString stringWithFormat:@"%d %@%@ ago",
            difference,
            unit,
            (pluralize ? @"s" : @"")];
  }
}

@end

NSDateFormatting2.m

- (NSString*) description {
  return [self timeAgoInWords];
}

pc.h

#import <Availability.h>

#ifndef __IPHONE_3_0
#warning "This project uses features only available in iPhone SDK 3.0 and later."
#endif

#ifdef __OBJC__
#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import <QuartzCore/QuartzCore.h>
#import <CoreText/CoreText.h>
#import "Extensions.h"

#endif

UsingNSDateFormatting.m

NSDate* oldDate = [NSDate dateWithTimeIntervalSinceNow:180];
NSLog(@"Date was %@", oldDate.timeAgoInWords);