Objective C Builder Pattern play

So I read two posts on the Builder Pattern from Java today that got linked to off of Twitter.

This by Klaas Pieter which referenced this one by Uli Kusterer.  Both good articles.

I haven’t done Java much at all for the last 10 years and so am not used to this pattern, but I thought about how I might do something similar and while I’m not sure my first thought is any better, it seems to meet the requirements and/or benefits noted by the two blog posts in question and the tweet discussion referencing them.

Instead of:

 Pizza pizza = new Pizza.Builder()

(from Uli’s post), or

  Image* theImage =
    (new Image.Builder)->SetWidth(100)

(from Klaas’ post)

I tried something like:

Foo * aFoo = [Foo fooWithData: @{
     @"width" : @21, @"height" : @22 }];

Here’s one way to implement that – there are multiple, clearly
(pardon the formatting, trying to fit into our narrow blog them is annoying):

// .h file
#import <Foundation/Foundation.h>

@interface Foo : NSObject

+ (instancetype) fooWithData: (NSDictionary*) initParams;


// .m file
@interface Foo ()
@property (nonatomic, assign) long width;
@property (nonatomic, assign) long height;
@property (nonatomic, assign) long depth;

@implementation Foo

+ (instancetype) fooWithData: (NSDictionary*) initParams
  Foo *result = [[Foo alloc] init];

  // If one uses setValue:forKey: in a loop as
  // as Uli notes then we can't support integral
  // properties like ints.
  // Also doing it explicitly as below
  // means we don't have to have the same name
  // for our private internal properties as we
  // document for our public parameters because
  // we can map them here.
  // e.g.,
  //  result.imageWidth = [initParams[@"width"] longValue];

  if ( initParams[@"width"] != nil )
    result.width = [initParams[@"width"] longValue];

  if ( initParams[@"height"] != nil )
    result.height = [initParams[@"height"] longValue];

  if ( initParams[@"depth"] != nil )
    result.depth = [initParams[@"depth"] longValue];

  return result;

- (instancetype) init
  self = [super init];
  if ( self )
    // init with defaults
    _width = 10;
    _height = 10;
    _depth = 1;
  return self;

- (NSString*) description
  return [NSString stringWithFormat:
           @"Foo: (%p), width: %ld, height: %ld, depth: %ld",
           self, self.width, self.height, self.depth];

// main.m
#import <Foundation/Foundation.h>

int main(int argc, char *argv[]) {
  @autoreleasepool {
      // note no depth specified, taking default of 1
    Foo * aFoo =
      [Foo fooWithData: @{ @"width" : @21, @"height" : @22 }];
    NSLog(@"aFoo: %@", aFoo );

Paste the above into CodeRunner and run it and you get:

2014-04-12 16:22:38.918 Untitled 7[71144:707]
aFoo: Foo: (0x7f8842c0af00), width: 21, height: 22, depth: 1

In the above I only typed in the class method as taking the full parameter list but normally I would have made the init method take the same parameter and do the initialization & mapping there. Something I’d likely add if I was going to actually use this, which I’m not likely to. Why not? Because to use the construct above you’d have to document the parameter keys available to use in the dictionary and what type of value each takes. This is where ObjectiveC’s named parameters comes in handy: they are self documenting.

Anyway, an interesting procrastination from what I was supposed to be doing this Saturday afternoon… 🙂

7DRL 2014 – Day 7: In which everything is complete

Trinkets – the roguelike game I’ve spent the past week creating for the 7DRL competition – is finished, about 20 hours before the deadline! It’s a game about wandering an extra dimensional vault, acquiring trinkets and trying to get back home.

A build for mac is available here. Unfortunately, there’s no windows/linux build, but if you’re on one of those operating systems and want to play, the source is available here.

Screen Shot 2014-03-15 at 2.38.31 PM

… which turns out to be entirely justified.

My high score is 59 – can you beat it? If so, let me know in the comments below!

7DRL 2014 – Day 6: In which victory approaches at high velocity

One day remains, and I’m actually almost done. It would be nice to redo the map generator, and game balance can always be tweaked some more, but the plot and endgame are implemented, the boss-fights are done with basic AI, and there’s even a score feature. Shown below is the second of four boss fights:

You have a bad feeling about this level...
You have a bad feeling about this level…
… which turns out to be entirely justified.
… which turns out to be entirely justified.

7DRL 2014 – Day 5: In which parkour is performed in fancy shoes

Today was very productive; I finished the procedural generation of trinkets (for now, at least), improved the magic system, procedurally generated strangely worded descriptions of said trinkets, added new effects including knock-back and circular slide, and added all of the non-boss enemies, including the Abberant visible below:

Parkour shoes acquired!

Shown above is the non-procedurally-generated description of one of the coolest shoe types in the game (thus far, at least). These shoes allow you to run along walls, moving faster than enemies or even jumping over them.

I still have two more days left to go, and quite a bit still to do, including:

  • Plot
  • Victory conditions
  • Boss fights + Boss AI
  • Game balance
  • Prettier maps

7DRL 2014 – Days 3 and 4: In which trinkets are created

So, I’m about halfway through the week, but days 2-4 were all mostly occupied by other things, so the real productivity is just beginning. I’ve reworked the combat system to use the same generalized targeting/effect model as the spells. I’ve also changed trinket abilities to work on that model, divided trinkets into six types (hats, orbs, wands, cloaks, weapons, and shoes), which can be equipped and used for various nefarious purposes. I’ve started work on the procedural generation of trinkets, but there’s still a lot to do on that front, which will occupy the next day and a half, leaving me with a day and a half for enemies, plot, game balance, and a dungeon generator that isn’t stolen from the libtcod tutorial. That’s plenty of time, right?

Screen Shot 2014-03-12 at 11.36.07 PM
Weapons can now replace your bump attack with one or two spell casts. This one replaces your attack with two fire bolts, but they can also sunder defenses or daze and freeze enemies, among other things.
Screen Shot 2014-03-11 at 9.38.44 PM
Death Star? Death Star! DEATH STAR!
This is what happens when you procedurally generate names by picking two words from a list and concatenating them…


7DRL Competition 2014 – Day 2: In which the art of sorcery is practiced

Screenshot of Trinkets
Magic system: Activate!

There are now six spells, and status effects, and some of the ‘everything goes horribly wrong’.

The spells have all been divided into ‘targeting’ and ‘effect’ components – except for teleportation, which still consists of duct tape and hacks and probably will remain that way.

There’s also a bit more user interface than before, and the trinkets are actually worth using sometimes (even if they are all still exactly identical).

Melee combat has also been re-written to allow for spells like the Ethereal Axe, which replaces your melee attack with a high-damage Arcane attack.

Tomorrow, I’ll be working on equipment. I won’t have much time though – classes and whatnot – so there probably won’t be a blog post.

The day after, procedural trinkets, more enemies, and everything going even more horribly wrong!

7DRL Competition 2014 – Day 1: In which a roguelike is begun

This year I’m participating in the Seven Day Roguelike Competition, a contest to make a game in the roguelike genre in a week. (For those not familiar with it, roguelikes tend to be dungeon-crawlers with procedurally generated words, permanent character death, and often old-school graphics. There are frequently some variations from this rough description.)

I’m making a game known as ‘Trinkets’ until I think of a better name. It is a game in which a wizard strapped for cash loots a pocket dimension, and everything goes horribly wrong. It will experiment with a nontraditional power progression; you become weaker, then strong again, rather than a constant power level or steady increase. There will be a plot and randomly generated Trinkets.

My time will be somewhat limited, as I am currently a college student, but after spending most of today programming I produced the following:

Screenshot of Trinkets
Taste the power, troll scum!

I’ve used some code from some past projects, specifically most of the data structures and UI code. I’m using python, with the libtcod library.

Current features:

  • Move around…
  • …on a procedurally generated map…
  • …and hit things…
  • …which hit you back, and can kill you if you’re not careful.
  • Look for trinkets…
  • …which have magic powers…
  • …which are simply not as powerful (at least for now) as your spells.
  • Speaking of spells, you have five (and will have six), which in combination make you nearly unstoppable…
  • …at least until I implement the ‘everything goes horribly wrong’ part.

Simple BBEdit Text Filter that’s been useful: PrettyJSON.py

Dad’s been working with some JSON output from a web service lately and it comes back lacking line-feeds and indentation which is great for transmission but hard to read for humans.  Dad’s not a python programmer and Geek’s busy writing a Humanities 110 paper, but the simple python script PrettyJSON.py (below) seems to work if you put it into

~/Library/Application Support/BBEdit/Text Filters/

It can be used to beautify the front window in BBEdit if that contains JSON:

#!/usr/bin/env python
import fileinput
import json
if __name__ == "__main__":
  jsonStr = ''
  for a_line in fileinput.input():
    jsonStr = jsonStr + ' ' + a_line.strip()
  jsonObj = json.loads(jsonStr)
  print json.dumps(jsonObj, sort_keys=True, indent=2)

Because Bare Bones Software is so cool this works with their free Text Wrangler editor as well except you just put the files in

~/Library/Application Support/TextWrangler/Text Filters/

instead, as one would expect.

This gives you a new item in the “Text” -> “Apply Text Filter” sub-menu named whatever you named the file (PrettyJSON.py in my case).  Open a messy JSON file, select “Text” -> “Apply Text Filter” -> “PrettyJSON.py” and watch your file contents magically become beautiful! Thanks BBEdit!

Core Data – efficient fetching of portions of Entities

NOTE:  This is reported not to work on iOS 8+ (see comments).  This post is also fairly old at this point and I haven’t re-verified that it works on newer versions of OS X, though the relevant comment in NSFetchRequest.h seems to still be present in the 10.12 OS X SDK.

Quick write up of an active conversation on twitter and the results of some research.

Brent Simmons posted about something I’d started looking into today: Efficient Core Data fetching when you only need a few fields of a database Entity.  The name of setPropertiesToFetch: in NSFetchRequest looks promising however the documentation says:

This value is only used if resultType is set to NSDictionaryResultType.

Well that’s a bummer because we’d really like our nice subclass of NSManagedObject to be used by our view controller (say) or we only need to access one property of the complex object.  Here’s something odd I noticed though: the comment in the NSFetchRequest.h file (OS X 10.8 SDK & 10.9 SDK) for setPropertiesToFetch: says this:

If NSManagedObjectResultType is set, then NSExpressionDescription cannot be used, and the results are managed object faults partially pre-populated with the named properties

Well hey! That’s exactly what we want it to do for efficiency when we only need a couple of properties out of many for a given entity.

Thanks to some twitter dialog with @pgor and others, and especially a reminder from @JimRoepcke about setting -com.apple.CoreData.SQLDebug 1 to show the sql logging for Core Data when talking to an sqlite backend, I was able to verify that this does work the way we want it to, at least on OS X running under 10.8.4:

If you use code like the following:

NSFetchRequest * request = [NSFetchRequest fetchRequestWithEntityName: @"AppEntry"];
[request setPredicate: [NSPredicate predicateWithFormat: @"app_id in %@", inAppIDs]];
[request setIncludesSubentities: NO];
[request setPropertiesToFetch: @[ @"app_id", @"fooprop"]];
// [request setIncludesPropertyValues: NO]; // you need YES, which is the default
[request setResultType: NSManagedObjectResultType];
[request setReturnsObjectsAsFaults: NO]; // maybe not needed.  It will still be a fault,
                                         // but the properties are preloaded
NSError * error = nil;
NSArray * fetchedArray = [self.managedObjectContext executeFetchRequest: request error: &error ];
if ( fetchedArray != nil )
  if ( [fetchedArray count] > 0 )
    AppEntry * entry = [fetchedArray firstObject];
    NSLog(@" isFault? %@", entry.isFault ? @"YES" : @"NO" );
    NSNumber * appID = entry.app_id;
    NSLog(@" appID: %@", appID );
    NSLog(@" isFault? %@", entry.isFault ? @"YES" : @"NO" );
      // accessing property not in setPropertiesToFetch:
      // causes fault to fire & load whole object
    NSString * otherProperty = entry.otherProperty;
    NSLog(@" isFault? %@", entry.isFault ? @"YES" : @"NO" );
    NSLog(@"otherProperty: %@", otherProperty );
    NSLog(@"no resuts");

(code changed to mask client project details so typos are because of that)

and the output is:

// the fetch does this - only the two properties we indicated are fetched:
 CoreData: sql: SELECT t0.Z_ENT, t0.Z_PK, t0.ZAPP_ID, t0.ZFOO FROM 
                  ZAPPENTRY t0 WHERE t0.ZAPP_ID IN (?,?,?)
 isFault? YES
 appID: 281940292
 isFault? YES
 CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAPP_ID, t0.ZOTHERPROPERTY, 
                   t0.ZDATESTAMP, t0.ZNAME, t0.ZFOO, t0.ZTITLE FROM ZAPPENTRY t0 
                   WHERE t0.Z_PK = ?
 CoreData: annotation: sql connection fetch time: 0.0025s
 CoreData: annotation: total fetch execution time: 0.0030s for 1 rows.
 CoreData: annotation: fault fulfilled from database for : 0x100150590 ...
 isFault? NO
 otherProperty: it works!

So you can see that the main fetch request only grabbed the two properties that were in setPropertiesToFetch:. The result object is a faulted NSManagedObject (see where we checked isFault) but the property values for the properties listed in setPropertiesToFetch: are available without faulting the object and doing another database fetch. You’ll see we accessed appID to check this.

However, if you then access a property that was not in the setPropertiesToFetch: list (otherProperty in the above code) you can see that another sql call is made and the object is faulted and fully loaded.  The next check for isFault returns NO because it is no longer a fault.

So to me this indicates that setPropertiesToFetch: IS useful exactly as we’d like even when you’re not getting the NSDictionaryResultType and so is ideal for exactly the situation Brent was asking about for his timeline view.    I’ve filed a radar on the documentation error rdar://16073227 so hopefully that’ll get updated sooner than later.


I was curious if one could modify one of these limited properties without faulting the entire object and all of it’s properties (which seemed unlikely) and so I did an additional test and the answer is: nope.  Modifying a prefetched property on the object causes a fault and the whole object and all it’s properties are loaded into memory and isFault returns NO.

Update #2: 

So this technique above turns out to work and be handy when you only need to fetch an item in a one-to-many property/relation off of an object with lots of properties to avoid loading all those properties into memory.  In our sample data an AppEntry has a bunch of properties including a relation to a list of prices and we’d like the most recent price (just any price for this sample code) but we don’t need to load in the rest of the data in the App Entry entity.  Works like this:

NSFetchRequest * request = [NSFetchRequest fetchRequestWithEntityName: @"AppEntry"];
[request setPredicate: [NSPredicate predicateWithFormat: @"app_id == %@", inAppID]];
[request setIncludesSubentities: NO];
[request setReturnsObjectsAsFaults: NO];
[request setPropertiesToFetch: @[ @"app_id" ]];
[request setRelationshipKeyPathsForPrefetching: @[ @"prices" ]];
NSError * error = nil;
NSArray * fetchedArray = [self.managedObjectContext executeFetchRequest: request error: &error ];
if ( fetchedArray != nil )
  if ( [fetchedArray count] > 0 )
    AppEntry * appData = [fetchedArray firstObject];
    if ( appData != nil )
      PriceEntry * price = [appData.prices anyObject];
      NSLog(@"a price is: %@", price.price );

and the logging looks like this:

CoreData: sql: SELECT t0.Z_ENT, t0.Z_PK, t0.ZAPP_ID FROM ZAPPENTRY t0 WHERE t0.ZAPP_ID = ?
CoreData: annotation: sql connection fetch time: 0.0005s
CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZDATESTAMP, t0.ZPRICE, t0.ZAPP_ID
CoreData: annotation: sql connection fetch time: 0.0004s
CoreData: annotation: total fetch execution time: 0.0007s for 1 rows.
CoreData: annotation: Prefetching with key 'prices'. Got 1 rows.
CoreData: annotation: total fetch execution time: 0.0022s for 1 rows.
a price is: 0

So you can see that it only loads the app_id property from the AppEntry object but still you can get to the prices relation.  Unfortunately I’m not seeing a way to cascade the setPropertiesToFetch: down into the related entities and so all the fields in the PriceEntity in this example get fetched.  I’d love to find a way to do that so if you figure that out please let me know – thanks!

Update #3: 

(I know, I know! What’s with all these updates?! – I wanted to get the basics out there and then I kept thinking of other angles/aspects of this topic).

So one thing that might be helpful is to show how to use the -com.apple.CoreData.SQLDebug 1 setting to examine what Core Data is doing when you’re using it. Setting this was critical to understanding what was happening in the above research.  You want to pass this as an argument to your app. So if you’re launching your app from the terminal you’d pass -com.apple.CoreData.SQLDebug 1 as a command line argument as usual. If you’re running from within Xcode then you set the arguments to pass to your app in the Scheme settings which you access via Edit Scheme… or Manage Schemes… + Edit Scheme….  Here’s a screenshot of the Edit Scheme sheet where you can see how to enter this flag:

Set Command Line Agrument

NSURLConnection & GDC

Using NSURLConnection combined with GCD for the first time and noticed that if you invoke NSURLConnection on anything other than the main queue it seems to lock up and nothing happens.  Actually something happens but your delegate never gets called.  Easy fix though; you just need to set the delegate queue (or run loop) before starting the download.


Here’s some sample code setting the delegate queue for you to play with if you like. Just make a sample cocoa app from the standard template and then setup the application delegate like this

@interface AppDelegate ()
  @property (strong) NSURLConnection* connection;
  @property (strong) NSMutableData * downloadedData;

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
  // Insert code here to initialize your application

  dispatch_async( dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), 
      self.downloadedData = [NSMutableData new];
      NSURLRequest * request = [NSURLRequest requestWithURL: 
      [NSURL URLWithString: @"http://wp.me/av6Bm-pZ"]];
      self.connection = [[NSURLConnection alloc] initWithRequest: request 
                          delegate: self 
                        startImmediately: NO];  // This *must* be "NO". 
                                                // Can't switch delegate queue 
                                                // after download starts
      [self.connection setDelegateQueue: [NSOperationQueue mainQueue]];  // *** set queue
      [self.connection start];   // *now* you can start the fetch
      NSLog(@"request queued!");

// delegate calls just so let us know when it's working or when it isn't

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
    NSLog( @"download failed with an error: %@, %@", 
        error, [error description] );

    // release this stuff, test is done.
    self.connection = nil;
    self.downloadedData = nil;

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
    NSLog( @"connection did receive response: %@", response );

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
    NSLog(@"download data received %lu", [data length] );
    [self.downloadedData appendData: data];

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
    NSLog(@"didFinishLoading.  total data is: %lu", [self.downloadedData length] );

    // release this stuff, test is done.
    self.connection = nil;
    self.downloadedData = nil;


Line 22 is the key (the setDelegateQueue: call). If you leave that line out then you’ll wonder why it’s not downloading your data. If you change the queue passed to line 12 with dispatch_get_main_queue() then it’ll work without the setDelegateQueue: call).

Obvious once you see it but maybe this’ll save someone a bit of time.

P.S. This was done with Xcode 5 under 10.8.5 fwiw.