TweetFollow Us on Twitter

Dynamic Bundles Volume Number: 17 (2001)
Issue Number: 1
Column Tag: Mac OS X

Dynamic Bundles and Runtime Loading in OS X

By Andrew C. Stone

The Subtitle in Italics

As an application gets larger and more complex, the end user may perceive that the application loads slowly. Of course one can throw faster and multiple CPUs at the problem, but if you take advantage of dynamic bundle loading, your application can grow in functionality, but the time to launch remains lightning quick. How is this done? Simply by only loading the resources the user really needs at the moment. This article will show you how to architect your application to take advantage of bundles and late-loading.

Consider the fact that a typical application may have dozens of special panels and facilities that are occasionally accessed by the end user. There is no reason to load either the code or the resources for these panels until the end user actually requests that functionality.

There are many advantages to an application that dynamically loads bundles besides just fast launches. For example, in Stone Create, not only are all the inspectors, panels, and editors loaded on demand, but there is also a facility to load new tools at runtime. Any bundles found in the Tools directory are loaded and added to the tool palette when a new document is created. For example, the "Star" and "Embed" objects are loaded this way. New tools can be created and added without Create knowing anything about these in advance. By creating and adhering to protocols, which are sets of methods that must be implemented by an object, your application can deal with brand new objects at runtime.

The CFBundle, and its Cocoa cover class, NSBundle, handle all the details of locating and loading resources on demand. Most developers just use these for user interfaces, images, sounds and resource files, but it's simple to also load code on demand. The question then becomes, "how can I refer to code that is not yet loaded?" and "how can I compile code that has unresolved symbols"?

PreferencesController Bundle Example

One feature which makes OS X applications so powerful is the ease of user customization through the NSUserDefaults mechanism. Therefore, most applications require a user interface for preferences, but why load this panel and the code which controls it before it's absolutely needed if at all? We'll use the example of a preferences panel as a likely target for "bundling". The object "PreferenceController" is an NSWindowController subclass, which knows how to return a single instance of itself with a factory method, +sharedInstance:, because there is only one preferences panel in any application:

+ (id)sharedInstance {
    static PreferencesController *sharedPreferences = nil;

    // the first time through, we get the singleton preferences controller:
    if (!sharedPreferences) {
         sharedPreferences = [[PreferencesController                            allocWithZone:NULL] init];
    }

    return sharedPreferences;
}

Our dynamic loading code will assume that every bundle responds to "+ sharedInstance" if there are only one of these objects (for example, there is only one Color panel per application).

If PreferenceController is linked into the application, you would have a method to bring up the panel in your application delegate object:

- (IBAction)showPreferencesPanelAction:(id)sender {
   [[PreferenceController sharedInstance] showWindow:self];
}

but then, that code would be loaded at the launch of the application, because it has to be compiled into the application's binary since it is referenced by name. The way we move to a dynamicly loaded model is to never refer to this class, except in a string as an argument to our dyamic loading method sharedInstanceOfClassName:, which appears later in the article:

    [[self sharedInstanceOfClassName:@"PreferencesController"] showWindow:self];

Now, the code will compile without including the PreferencesController class. Our job is to be sure it gets loaded when first needed. Typically, I add the bundle loading code to the NSApplication's delegate, which can be globally accessed with:

[NSApp delegate]

Another strategy, and a topic of a later article, is to use categories, and add that functionality right to the NSBundle class. I prefer using the NSApp's delegate because you can add cover methods for loading panels in a single class, and then connect menu items to the instantiated application delegate in the application's main NIB file. So, in this example, we would:

  1. add a method to the NSApp delegate class:
    - (IBAction)showPreferencesPanelAction:(id)sender;
    
  2. In InterfaceBuilder, connect the menu item "Preferences..." to the app delegate target, with the action "showPreferencesPanelAction:". You can quickly add actions to IB by dragging in the .h or .m file from ProjectBuilder into the document window of your nib. This is equivalent to "Classes->Read File...".
  3. When that menu item gets triggered, the application delegate will load the needed code. Subsequent invocations of the panel will be even swifter, but loading a single panel and controller code is pretty fast anyway.

Bundle Integration in Project Builder

From a Project Builder standpoint, your application's project becomes an aggregate of targets: the application target, and a target for each of the dynamically loaded bundles. Your application should add the product of each bundle to the Copy Files phase in the "Files and Build Phases" tab of the application target inspector.


Figure 1. Copy files phase adds bundles to the application target.

For backwards compatibility with OpenStep, I use the "Resources" directory to store bundles. The following code assumes that you are putting your bundles into the Resources subdirectory in <YOUR_APP_NAME>.app/Contents/. You change where they are copied to with the "Where:" pop-up in the Files & Build Phases pane of the Target Inspector. It is probably more intuitive to place bundles in "Bundles" subdirectory, and if you do, change the pathForResource:ofType: call to pathForBundle:ofType: in the method -(id)instanceOfClassName:(NSString *)name shared:(BOOL)shared.

Before looking at the very simple dynamic loading code, there is one point to consider. A Cocoa bundle has the notion of a principal class. That is the class that is both the owner of the NIB file, and the class that needs to be accessed first when the bundle is loaded. Many times, a bundle will only have one class in it, but its a potential gotcha to not specify the principal class if there are more than one class in the bundle. You assign the principal class in Project Builder - click the bundle target to load the target inspector. Select the "Bundle Settings" tab, and under the "Cocoa Specific" settings, type in the name of the class in the Principal class field, in this example, PreferencesController. Other fields let you assign version information, help files, main nib files, but these are optional.

The Dynamic Loading Code

The code offers two types of dynamic code loading - both singleton class instances such as the PreferencesController with sharedInstanceOfClassName, as well as simple new instances for each invocation with instanceOfClassName. Both use the same core code with a "shared" flag:

- (id)sharedInstanceOfClassName:(NSString *)name
{
    return [self instanceOfClassName:name shared:YES];
}

- (id)instanceOfClassName:(NSString *)name {
   return [self instanceOfClassName:name shared:NO];
}

instanceOfClassName would be used, for example, in a document-based architecture application where each document had its own version of that bundle's nib. An example would be a sheet that gets run on a per-document basis - because more than one document can be in a sheet-modal state at the same time. In this case, the document becomes responsible for freeing the bundle resources upon closing. Singleton instances are not freed until the application quits.

- (id)instanceOfClassName:(NSString *)name shared:(BOOL)shared
{
    id obj = nil;
    // NSBundle does the work of finding the bundle
    // pathForResource means "look into Resources folder"
    // use pathForBundle if you store them in the "Bundles" folder
    NSString *path = [[NSBundle mainBundle] 
                              pathForResource:name ofType:@"bundle"];
    if (path) {
        NSBundle *b = [[NSBundle allocWithZone:NULL] 
                                                   initWithPath:path];

        // the object we wish to return is an instance of the principal class:
        if ((b != nil) && ([b principalClass] !=NULL)) {

      // we either grab the sharedInstance or create a new one:
      if (shared) obj = [[b principalClass] sharedInstance];
      else obj = [[[b principalClass] allocWithZone:NULL] init];

    // provide Developer feedback if something has gone wrong:
        }  else NSLog(@"Can't Load %@!\n", path);
    } else NSLog(@"Couldn't find %@ bundle!\n",name);

    return obj;
}

Conclusion

When designing your application, it is good practice to decompose your functionality into small, loadable pieces. By using dynamically loaded bundles, you gain launch speed and can take advantage of runtime binding for loading new tools. Probably most importantly, bundles create a firm foundation for future feature growth without application bloat as well as provide a natural modularity that is easy to comprehend.


Andrew Stone <andrew@stone.com> is CEO of www.stone.com and has been working with Cocoa since 1989 with its introduction as NeXTStep.

 
AAPL
$99.02
Apple Inc.
+1.35
MSFT
$43.97
Microsoft Corpora
-0.53
GOOG
$590.60
Google Inc.
+1.58

MacTech Search:
Community Search:

Software Updates via MacUpdate

OS X Yosemite Wallpaper 1.0 - Desktop im...
OS X Yosemite Wallpaper is the gorgeous new background image for Apple's upcoming OS X 10.10 Yosemite. This wallpaper is available for all screen resolutions with a source file that measures 5,418... Read more
Acorn 4.4 - Bitmap image editor. (Demo)
Acorn is a new image editor built with one goal in mind - simplicity. Fast, easy, and fluid, Acorn provides the options you'll need without any overhead. Acorn feels right, and won't drain your bank... Read more
Bartender 1.2.20 - Organize your menu ba...
Bartender lets you organize your menu bar apps. Features: Lets you tidy your menu bar apps how you want. See your menu bar apps when you want. Hide the apps you need to run, but do not need to... Read more
TotalFinder 1.6.2 - Adds tabs, hotkeys,...
TotalFinder is a universally acclaimed navigational companion for your Mac. Enhance your Mac's Finder with features so smart and convenient, you won't believe you ever lived without them. Tab-based... Read more
Vienna 3.0.0 RC 2 :be5265e: - RSS and At...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more
VLC Media Player 2.1.5 - Popular multime...
VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It... Read more
Default Folder X 4.6.7 - Enhances Open a...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click... Read more
TinkerTool 5.3 - Expanded preference set...
TinkerTool is an application that gives you access to additional preference settings Apple has built into Mac OS X. This allows to activate hidden features in the operating system and in some of the... Read more
Audio Hijack Pro 2.11.0 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more
Intermission 1.1.1 - Pause and rewind li...
Intermission allows you to pause and rewind live audio from any application on your Mac. Intermission will buffer up to 3 hours of audio, allowing users to skip through any assortment of audio... Read more

Latest Forum Discussions

See All

Traps n’ Gemstones Review
Traps n’ Gemstones Review By Campbell Bird on July 28th, 2014 Our Rating: :: CASTLEVANIA JONESUniversal App - Designed for iPhone and iPad Fight mummies, dig tunnels, and ride a runaway minecart to discover ancient secrets in this... | Read more »
The Phantom PI Mission Apparition Review
The Phantom PI Mission Apparition Review By Jordan Minor on July 28th, 2014 Our Rating: :: GHOSTS BUSTEDUniversal App - Designed for iPhone and iPad The Phantom PI is an exceedingly clever and well-crafted adventure game.   | Read more »
More Stubies Are Coming Your Way in a Ne...
More Stubies Are Coming Your Way in a New Update Posted by Jessica Fisher on July 28th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
The Great Prank War Review
The Great Prank War Review By Nadia Oxford on July 28th, 2014 Our Rating: :: PRANKING IS SERIOUS BUSINESSUniversal App - Designed for iPhone and iPad Though short, The Great Prank War offers an interesting and fun mix of action and... | Read more »
Marvel Contest of Champions Announced at...
Marvel Contest of Champions Announced at Comic-Con Posted by Jennifer Allen on July 28th, 2014 [ permalink ] Announced over the weekend at San Diego Comic-Con was the fairly exciting looking Marvel Contest of Champions. | Read more »
Teenage Mutant Ninja Turtles Review
Teenage Mutant Ninja Turtles Review By Jennifer Allen on July 28th, 2014 Our Rating: :: DULL SWIPINGUniversal App - Designed for iPhone and iPad The pizza power is weak when it comes to this Teenage Mutant Ninja Turtles game.   | Read more »
Exploration Focused Puzzle Game Beatbudd...
Exploration Focused Puzzle Game Beatbuddy Set to Make Transition from PC to iOS this September Posted by Jennifer Allen on July 28th, 2014 [ permalink ] | Read more »
PlanetHD
PlanetHD By Nadia Oxford on July 28th, 2014 Our Rating: :: SPACE MADNESSUniversal App - Designed for iPhone and iPad PlanetHD will keep players busy for a while, though its unpredictable physics are a handful to deal with.   | Read more »
This Week at 148Apps: July 21-25, 2014
Another Week of Expert App Reviews   At 148Apps, we help you sort through the great ocean of apps to find the ones we think you’ll like and the ones you’ll need. Our top picks become Editor’s Choice, our stamp of approval for apps with that little... | Read more »
Reddme for iPhone - The Reddit Client (...
Reddme for iPhone - The Reddit Client 1.0 Device: iOS iPhone Category: News Price: $.99, Version: 1.0 (iTunes) Description: Reddme for iPhone is an iOS 7-optimized Reddit client that offers a refreshing new way to experience Reddit... | Read more »

Price Scanner via MacPrices.net

13-inch 2.5GHz MacBook Pro on sale for $1099,...
Best Buy has the 13″ 2.5GHz MacBook Pro available for $1099.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $100 off MSRP. Price is... Read more
Roundup of Apple refurbished MacBook Pros, th...
The Apple Store has Apple Certified Refurbished 13″ and 15″ MacBook Pros available for up to $400 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. Their prices... Read more
Record Mac Shipments In Q2/14 Confound Analys...
A Seeking Alpha Trefis commentary notes that Apple’s fiscal Q3 2014 results released July 22, beat market predictions on earnings, although revenues were slightly lower than anticipated. Apple’s Mac’... Read more
Intel To Launch Core M Silicon For Use In Not...
Digitimes’ Monica Chen and Joseph Tsai, report that Intel will launch 14nm-based Core M series processors specifically for use in fanless notebook/tablet 2-in-1 models in Q4 2014, with many models to... Read more
Apple’s 2014 Back to School promotion: $100 g...
 Apple’s 2014 Back to School promotion includes a free $100 App Store Gift Card with the purchase of any new Mac (Mac mini excluded), or a $50 Gift Card with the purchase of an iPad or iPhone,... Read more
iMacs on sale for $150 off MSRP, $250 off for...
Best Buy has iMacs on sale for up to $160 off MSRP for a limited time. Choose free home shipping or free instant local store pickup (if available). Prices are valid for online orders only, in-store... Read more
Mac minis on sale for $100 off MSRP, starting...
Best Buy has Mac minis on sale for $100 off MSRP. Choose free shipping or free instant local store pickup. Prices are for online orders only, in-store prices may vary: 2.5GHz Mac mini: $499.99 2.3GHz... Read more
Global Tablet Market Grows 11% in Q2/14 Notwi...
Worldwide tablet sales grew 11.0 percent year over year in the second quarter of 2014, with shipments reaching 49.3 million units according to preliminary data from the International Data Corporation... Read more
New iPhone 6 Models to Have Staggered Release...
Digitimes’ Cage Chao and Steve Shen report that according to unnamed sources in Apple’s upstream iPhone supply chain, the new 5.5-inch iPhone will be released several months later than the new 4.7-... Read more
New iOS App Helps People Feel Good About thei...
Mobile shoppers looking for big savings at their favorite stores can turn to the Goodshop app, a new iOS app with the latest coupons and deals at more than 5,000 online stores. In addition to being a... Read more

Jobs Board

Sr Software Lead Engineer, *Apple* Online S...
Sr Software Lead Engineer, Apple Online Store Publishing Systems Keywords: Company: Apple Job Code: E3PCAK8MgYYkw Location (City or ZIP): Santa Clara Status: Full Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Sr. Product Leader, *Apple* Store Apps - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.