TweetFollow Us on Twitter

The Road to Code: Custom House

Volume Number: 26
Issue Number: 01
Column Tag: The Road to Code

The Road to Code: Custom House

Creating and using custom frameworks

by Dave Dribin

Introduction

We've talked at length about the system provided frameworks, namely Foundation and AppKit. This month we're going to learn a little bit more about frameworks and how to create and use your own custom frameworks.

Libraries

In order to understand frameworks, we need to take a few steps back and talk about how source files are actually turned into an executable program. For C-based languages, including Objective-C, turning source code into a program consists of a two-step process involving tools called a compiler and linker. In the first stage, the compiler turns source files into object files. Source files have file extensions of .c for C source code or .m for Objective-C source code. Object files have .o extension, no matter what the source language is. The linker takes all the object files and combines them into the final executable, sometimes called a binary.


Figure 1: Compile and link process

Figure 1 shows how two C source files, file1.c and file2.c, are turned into an executable named program. The compiler turns file1.c into file1.o and file2.c into file2.o by a process known as compiling. The linker then combines file1.o and file2.o into the final executable named program by a process known as linking. Objective-C programs are compiled in exactly the same manner, except the source files have a .m extension.

This two-step compile and link process helps scale programs to many source files. It allows developers to split up code into multiple source files in a way that make sense for the project. This not only helps from an organizational standpoint, but helps speed up compile times. If you change one function, only the source file that contains it needs to be recompiled. All other object files can be re-used when linking the final executable.

Static Libraries

A library, in a generic sense, is a bit of code that is designed to be used and shared among many applications. Back in the early days of C programming, it became clear that there were common needs that most programs had, such as manipulating strings and handling file I/O. Instead of having each program write these from scratch every time, wouldn't it be better if you could use the same functions from application to application? This would save time and help reduce bugs.

Prior to the invention of libraries, each program wanting to share code between them had only one option: share the source files. Say we had string manipulation functions in a file named string.c, each program would need their own copy of this file. While this is fine if the shared code can fit into one file, if the shared code gets big enough to be split into multiple files, this can become unwieldy. Plus, why bother having each application compile the same source files over and over again, when they could share the object files?

Enter static libraries. Static libraries combine multiple object files into a single file called a static library. The linker can then use the static library to pull in shared code. Say we've got XML parsing code we want to share among applications, and we want to create an XML static library. First, we compile all our XML related files into a single static library. Figure 2 shows this process. The source files are compiled as usual, but instead of linking them together into an executable, a tool called the archiver combines all the object files into a static library. Static libraries have the .a extension, but they are also always prefixed with lib. Thus libxml.a is file name of the static library named xml.


Figure 2: Create static library

Using this static library is fairly easy. Figure 3 shows a program that feeds libxml.a to the linker. The linker will pull the shared XML parsing code into the executable, along with its object files.


Figure 3: Link with static library

Dynamic Libraries

While static libraries are a big improvement over manually including shared code in every project, they're not without limitations. Since the shared code is included in each of the final executables, each executable takes up more disk space. For example, if a static library is 20 megabytes in size, every executable will contain this same 20 megabytes of code, wasting disk space. Also, if the library is updated to fix a bug, each of the executables must be re-linked to pull in the new code.

In order to help combat these issues, a new kind of library was created called a dynamic library. In Windows, a dynamic library is called a dynamically linked library, or DLL, and in Linux a dynamic library is called shared library. A dynamic library has a .dyld extension on Mac OS X but the same lib prefix as static libraries. To continue our example from earlier, the XML dynamic library would be named libxml.dyld.

Dynamic libraries are linked into an application in a similar fashion to static libraries, by telling the linker about them. The big difference is that the code is not copied into the resultant executable, but a reference to the dynamic library is recorded in the final executable. When the executable is run, the operating system finds the dynamic library file and pulls the code into the program at runtime. Because of this, the executable needs the dynamic library at runtime. This is not the case for static libraries.

Because the code is not copied to the executable, the file size of the executable is smaller. However, the big benefit of dynamic libraries is that the version of the dynamic library used at runtime does not need to be the same as the version linked against. Thus, if the system includes an XML library, and it gets updated to fix a bug, you don't have to re-link to get the fixed bug in your program. It will automatically use the new library when it runs.

Frameworks

One issue with both static and dynamic libraries is that the library file only contains compiled code. The API for the library is defined in header files. The typical convention on Unix systems is to place static and dynamic libraries in /usr/lib for system installed libraries and the corresponding header files go into /usr/include. By splitting the API from the library into two separate directories, it's hard to know which header files are for which library. Also, installing new libraries must be done carefully to not clash with existing libraries.

The fine folks at Apple (well NeXT, actually) decided to utilize bundles to help solve this problem. In case you don't remember, bundles are just directories with a special file extension. For example, Cocoa applications are bundles that use the .app file extension. Figure 4 shows what the directory structure of a simple application bundle looks like. Normally, the Finder hides all this from the user, but you can see it by choosing Show Package Contents from the Finder's contextual menu. The bundle contains the actual executable in the Contents/MacOS directory, but the application can contain other resources such as nib files, images, and localized strings. Putting all assets of an application into one bundle makes it easy for users to install and remove applications.


Figure 4: Application bundle contents

Frameworks are another kind of bundle that contains a dynamic library, along with its header files. It can even contain other resources such as images and Interface Builder plug-ins. Packing all of these related files together into a single directory makes distributing and updating shared code even easier.

Almost all shared Objective-C code is distributed as frameworks. Foundation and AppKit are the frameworks we are most familiar with. But we, too, can create our own frameworks. What if we want to share code between multiple applications? Or we have some nifty code that we think others will want to use in their applications, too? We're going to cover how to create our own frameworks.

Creating a Custom Framework

We are going to walk through creating an application that uses an embedded custom framework. The application will be called Hello World and the framework will be called HelloKit. We'll also put each of these in their own Xcode project and show how to link two Xcode projects together. Let's start off by creating the framework.

Start off by creating a new project using the Cocoa Framework template and name it HelloKit. Add a new class to the project named HelloObject and update the header file to match Listing 1 and the implementation to match Listing 2.

Listing 1: HelloObject.h

#import <Foundation/Foundation.h>
@interface HelloObject : NSObject
{
}
- (NSString *)greeting;
@end

Listing 2: HelloObject.m

#import "HelloObject.h”
@implementation HelloObject
- (NSString *)greeting;
{
    return @”Hello World!”;
}
@end

As you can see, this is a very simple class for demonstration purposes only. It's customary for frameworks to have a master header file with the same name as the framework that pulls in all header files for the entire framework. An example of this is the #import statement on the first line of the HelloObject.h file that includes the Foundation framework. Even though we've only got one class file right now, it's good to plan for the long term and create our own master header file. Create a new header file and name it HelloKit.h. It's going to be very simple right now, just one line of code:

#import <HelloKit/HelloObject.h>

And that's all the code we have to do for our framework. We have to mark our header files as public so that they are copied into the framework bundle. To do this, select the HelloKit target, and then change the Role of our two headers from project to public as shown in Figure 5.


Figure 5: Public headers

Before we can use this framework in another application, we need to learn a bit more about how Mac OS X locates frameworks used by an application.

Install Names

Every framework knows where it is supposed to be installed on the file system. This is called the install name and is recorded inside the framework. For example, all system provided frameworks are located in /System/Library/Frameworks, and their install name matches this. You can view the install name of a framework using the otool command line utility with the –D option:

% otool -D /System/Library/Frameworks/Foundation.framework/Foundation 
/System/Library/Frameworks/Foundation.framework/Foundation:
/System/Library/Frameworks/Foundation.framework/Versions/C/Foundation

When you link against a framework, the application also remembers the install name. When the application is run, it looks for the framework where the install name says it should be. This is fine for system-installed frameworks. They'll always be in /System/Library/Frameworks. But where does our custom framework live? It can actually be in a number of places:

/Library/Frameworks,

~/Library/Frameworks,

or embedded directly into an application or other framework bundle.

Because there is no way for us to foresee all uses, and there's only one install name, we have to pick one of theses locations. What does the Xcode template use for frameworks? Open up the build settings for the HelloKit target and search for "install” as in Figure 6.


Figure 6: Default install name

As you can see, it's using our home directory. This isn't useful for us, because we want to embed this framework into our application. If we use the default install name, it won't be able to find the framework. Before I explain how to fix this, I ought to tell you that embedded frameworks go in a directory named Contents/Frameworks inside the application bundle. Thus, our Hello World application should have the directory structure shown in Figure 7.


Figure 7: Application bundle with a framework

@loader_path

Since a user can install the application anywhere, we don't want to use /Applications as our install name. Mac OS X has special keywords that provide us with the flexibility we are looking for. In Mac OS X 10.4 and later, you can use the @loader_path keyword, by changing the Installation Directory of the framework to:

@loader_path/../Frameworks

Let's parse this out. @loader_path is a special keyword that gets substituted with the path of the actual executable. For our Hello World application, this path will be:

Hello World.app/Contents/MacOS/Hello World

The .. tells Mac OS X to go up to the parent directory, Contents, and the look for a directory named Frameworks there. The final, expanded out path would be:

Hello World.app/Contents/Frameworks

@loader_path works not only for applications but for frameworks that embed other frameworks and plug-ins that embed frameworks, too.

On Mac OS X 10.3 and earlier, @loader_path wasn't available, but a keyword called @executable_path was available that pointed to the running application's executable. This worked fine for frameworks embedded in applications, but didn't allow for frameworks to be embedded into other frameworks or plug-ins. You really shouldn't use @executable_path anymore, but I wanted to explain it in case you saw it in other projects.

@rpath

The @loader_path keyword still has some limitations, however. It means you must install the framework embedded inside another application or bundle. You can't install it in the home directory, either. This typically led developers to create embeddable and non-embeddable versions of the framework. The problem is that a framework distributor doesn't know exactly where the framework will eventually be used, yet it has to chose a single installation directory. Since this is not ideal, Mac OS X 10.5 comes with a new keyword called @rpath. This keyword allows the user of the framework to decide where the framework will be installed rather than the framework distributor.

To use @rpath, set the Installation Directory to be only @rpath, as shown in Figure 8.


Figure 8: rpath install name

With this in place, we can now move on to embedding this framework into our application.

Embedding a Framework

Create a new Cocoa application project called Hello World and add a new class called HelloWorldAppDelegate. This is standard so far, but it's about to get a bit tricky, so hang in there. We'll be fiddling around with some parts of Xcode we haven't used before.

Locate the HelloKit.xcodeproj file in the Finder and drag it directly into the Groups & Files section of the Hello World project. It should be added to the list, and you should be able to see the HelloKit framework underneath the sub-project as shown in Figure 9.


Figure 9: Embedded project

With the Hello World application target selected, choose Project > New Build Phase > New Copy Files Build Phase. Change the Destination to Frameworks as shown in Figure 10.


Figure 10: Copy files phase

Next, open the disclosure triangle to the Hello World target, and rename the new Copy Files phase to be Copy Frameworks. Finally, move it between the Copy Bundle Resources and the Compile Sources build phases, as shown in Figure 11.


Figure 11: Build phase order

Now that we've got our build target set up to copy over embedded frameworks into the correct directory, we've got to use this for the HelloKit framework. We want to make sure that the framework is built before the application, so double click on the Hello World target and add the framework as a direct dependency of the application, as shown in Figure 12.


Figure 12: Adding a target dependency

Setting up the dependency builds the framework before the application gets built, but we still need to copy the framework into our bundle and link against the framework. Drag the HelloKit.framework product into both the Copy Frameworks and Link Binary with Libraries phases, as shown in Figure 13.


Figure 13: Copy and link framework

We've got to change a couple more build settings of the application, and then we're done messing around with the target. As it stands, Xcode does not know where to find the framework at compile time. We need to setup the Framework Search Paths for the application target. Again, double click on the target and add the following to Framework Search Paths:

$(BUILT_PRODUCTS_DIR)/$(FRAMEWORKS_FOLDER_PATH)

The resulting build setting window is shown in Figure 14.


Figure 14: Framework search paths

The final build setting we need to set is the Runtime Search Paths. Remember that we used @rpath as the install name of our framework. Setting the Runtime Search Paths allows us to control what @rpath expands out to be. Since we copied the framework to our embedded Contents/Framework directory, we want to set the Runtime Search Paths to:

@loader_path/../Frameworks

The resulting build setting window is shown in Figure 15.


Figure 15: Runtime search paths

Notice that we're again using the @loader_path keyword, since that expands to the executable of our application. With all that grunt work out of the way, we're finally able to use our framework. We've set up our application target to build the framework target, copy it into our application bundle, and properly link against it. Now it's time to use this framework. Fortunately, this part is easy.

Make the HelloWorldAppDelegate implementation file look like Listing 3.

Listing 3: HelloWorldAppDelegate.m

#import "HelloWorldAppDelegate.h”
#import <HelloKit/HelloKit.h>
@implementation HelloWorldAppDelegate
- (void)awakeFromNib
{
    HelloObject * hello = [[HelloObject alloc] init];
    NSString * greeting = [hello greeting];
    [hello release];
    NSLog(@”Greeting: %@”, greeting);
}
@end

We import the master include file of the HelloKit framework at the top of the file. Then, we use the HelloObject class in awakeFromNib. Make sure an instance of HelloWorldAppDelegate is instantiated in the nib, and run the application. You should get the following output in the console:

Greeting: Hello World!

Conclusion

Whew! This is a lot of work to go through for such a simple framework, but the same steps can be applied to custom frameworks of any size. Xcode can be a fickle beast sometimes, so double-check all the steps carefully if things aren't working out. As usual, the project may be downloaded from the MacTech website, as well. If you're having issues, compare your project against the working version.


Dave Dribin has been writing professional software for over eleven years. After five years programming embedded C in the telecom industry and a brief stint riding the Internet bubble, he decided to venture out on his own. Since 2001, he has been providing independent consulting services, and in 2006, he founded Bit Maki, Inc. Find out more at http://www.bitmaki.com/ and http://www.dribin.org/dave/.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

FileMaker Pro 19.4.2 - Quickly build cus...
FileMaker Pro is the tool you use to create a custom app. You also use FileMaker Pro to access your app on a computer. Start by importing data from a spreadsheet or using a built-in Starter app to... Read more
Adobe Illustrator 26.0.3 - Professional...
You can download Adobe Illustrator for Mac as a part of Creative Cloud for only $20.99/month. Adobe Illustrator for Mac is the vector graphics classics in the design industry. It is a digital... Read more
WhatRoute 2.4.9 - Geographically trace o...
WhatRoute is designed to find the names of all the routers an IP packet passes through on its way from your Mac to a destination host. It also measures the round-trip time from your Mac to the router... Read more
Notion 2.0.20 - A unified workspace for...
Notion is the unified workspace for modern teams. Notion Features: Integration with Slack Documents Wikis Tasks Release notes were unavailable when this listing was updated. Download Now]]> Read more
Monterey Cache Cleaner 17.0.2 - Clear ca...
Monterey Cache Cleaner is an award-winning general-purpose tool for macOS X. MCC makes system maintenance simple with an easy point-and-click interface to many macOS X functions. Novice and expert... Read more
Firetask Pro 4.6.8 - Innovative task man...
Firetask Pro represents the next generation of easy-to-use, project-oriented task management apps. By combining David Allen's powerful Getting Things Done (GTD®) approach with classical task... Read more
Smultron 13.0.4 - Easy-to-use, powerful...
Smultron 13 is the text editor for all of us. Smultron is powerful and confident without being complicated. Its elegance and simplicity helps everyone being creative and to write and edit all sorts... Read more
Box Sync 4.0.8057 - Online synchronizati...
Box Sync gives you a hard-drive in the Cloud for online storage. Note: You must first sign up to use Box. What if the files you need are on your laptop -- but you're on the road with your iPhone? No... Read more
Audio Hijack 3.8.10 - Record and enhance...
Audio Hijack (was 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... Read more
Direct Mail 6.0.1 - Create and send grea...
Direct Mail is an easy-to-use, fully-featured email marketing app purpose-built for macOS. Create, send, and track great looking email campaigns that get results. Start your newsletter by selecting... Read more

Latest Forum Discussions

See All

Hopefully Not Jared’s Last Show – The To...
My suspicions from last week were correct, and after my two kids tested positive for Covid last week both my wife and I have now tested positive as well. It seems you just can’t escape this stuff lately. Thankfully the two little ones are pretty... | Read more »
TouchArcade Game of the Week: ‘Micro RPG...
I feel like idle games are one of those perfect fits for the mobile platform. Not that they replace more involved gaming experiences when you’re in the mood for that, but they do fit in alongside other types of games just fine as a “go to" when you... | Read more »
‘Phantom Blade: Executioners’ Closed Bet...
Phantom Blade: Executioners is holding a small-scale technical test that lets players get first dibs on the KungFuPunk action RPG. Offered to selected players only, S-Game’s first Closed Beta Test will provide players with limited edition in-game... | Read more »
New ‘Warhammer 40,000: Tacticus’ Video S...
Back in September Snowprint Studios, who you may know from their previous Legend of Solgard or Rivengard, announced that they’d partnered up with Games Workshop to put out a new tactical game in the Warhammer 40,000 universe titled Warhammer 40,000... | Read more »
SwitchArcade Round-Up: ‘Pokemon Legends:...
Hello gentle readers, and welcome to the SwitchArcade Round-Up for January 28th, 2022. We’ve got a bunch of new releases to look at today, with a few big hitters, a few mid-level diversions, and a healthy supply of compost. Since it’s Friday, we... | Read more »
Phantom Blade: Executioners, S-Game...
S-Game has kicked off its first Closed Beta Test for Phantom Blade: Executioners, inviting a selected few to get first dibs on the upcoming KungFuPunk action RPG on mobile. The CBT officially begins this January 28th, and beta testers will receive... | Read more »
‘Infinite Galaxy’ First Anniversary: Cel...
Cultivating a new generation of valiant commanders across 240 countries worldwide, Infinite Galaxy has quenched players’ thirst to explore the vastness of space – and there are only more intergalactic adventures to embark on from here on out. Camel... | Read more »
War and Order: How to brave the cold in...
War and Order's 6th-anniversary celebrations are underway, and all in good time too - this season not only brings about fabulous festivities, but it also lets players experience the harsh winter in an entirely new way. [Read more] | Read more »
‘Hidden Folks+’ Is This Week’s New Apple...
The original Hidden Folks from Adriaan de Jongh is an excellent hidden objects game featuring hand drawn visuals. It is an absolute joy to play, and it has now released on Apple Arcade in the form of Hidden Folks+ () as an App Store great. If you’... | Read more »
Mini Metro’s First Big Update of 2022 Ad...
Last year saw great updates for Dinosaur Polo Club’s Mini Metro ($3.99) which is also available on Apple Arcade as an App Store Great. | Read more »

Price Scanner via MacPrices.net

Apple has clearance 2020 13″ MacBook Airs ava...
Apple has clearance, Certified Refurbished, 2020 13″ Intel-based MacBook Airs in stock today starting at only $719 and up to $370 off original MSRP. Each MacBook features a new outer case, comes with... Read more
The cheapest iPhones for sale today at Apple...
Apple has restocked Apple Certified Refurbished iPhone 8 models starting at only $359. Each refurbished iPhone comes with a fresh external case, standard Apple 1-year warranty, and free shipping.... Read more
14″ MacBook Pro with Apple M1 Max CPU now in...
Looking for a new 14″ MacBook Pro with an Apple M1 Max CPU? Stock is finally trickling into Apple resellers. B&H has Silver 14″ M1 Max MacBook Pros in stock today for $2899 including free 1-2 day... Read more
14″ MacBook Pros with Apple M1 Pro CPUs are i...
Amazon is reporting stock of 14″ MacBook Pros with M1 Pro CPUs today with a $50 discount. Shipping is free, and delivery is available by February 1st for most configurations. Be sure to make your... Read more
Apple has restocked 13″ M1 MacBook Pros for $...
Apple has restocked a full line of 13″ M1 MacBook Pros available Certified Refurbished, starting at only $1099 and up to $230 off original MSRP. These are the cheapest M1 MacBook Pros for sale today... Read more
Apple’s AirPods Max headphones are on sale fo...
Amazon has Silver, Blue, and Space Gray Apple AirPods Max headphones on sale today for $100 off MSRP. Shipping is free, and all models are in stock today. Their price is the lowest currently... Read more
Open a new line of service at Verizon and get...
Verizon is giving away 64GB Apple iPhone 12 minis or your choice of an iPhone 11 to customers who choose one of these phones and open a new line of service. Offer is available online only, and no... Read more
Open-box 13″ M1 MacBook Airs now available st...
QuickShip Electronics has open-box return 13″ M1 MacBook Airs in stock and on sale for $200-$400 off MSRP on their eBay store right now with free express delivery. According to QuickShip, “The item... Read more
Verizon’s 2022 iPad promo: $100-$310 off any...
Verizon has cellular-capable iPads on sale for $100-$310 off MSRP when purchased with an Unlimited service plan. Sale price is applied to your account monthly over a 24 or 30 month period, depending... Read more
Sunday Sale: Apple AirPods are on sale for up...
Amazon has Apple AirPods on sale for $10-$100 off MSRP today, depending on the model. All are in stock today with free delivery: – AirPods Max headphones (Blue): $449 $100 off MSRP – AirPods Max... Read more

Jobs Board

Registered Nurse (RN) Employee Health PSJH -...
…is calling for a Registered Nurse (RN) Employee Health PSJH to our location in Apple Valley, CA.** We are seeking a Registered Nurse (RN) Employee Health PSJH to be Read more
Systems Administrator - Pearson (United State...
…and troubleshoot Windows operating systems (workstation and server), laptop computers, Apple iPads, Chromebooks and printers** + **Administer and troubleshoot all Read more
IT Assistant Level 1- IT Desktop Support Anal...
…providing tier-1 or better IT help desk support in a large Windows and Apple environment * Experience using IT Service Desk Management Software * Knowledge of IT Read more
Human Resources Business Partner PSJH - Provi...
…**is calling a** **Human Resources Business Partner, PSJH** **to our location in Apple Valley, CA.** **Applicants that meet qualifications will receive a text with Read more
Manager Community Health Investment Programs...
…is calling a Manager Community Health Investment Programs PSJH to our location in Apple Valley, CA.** **Qualified candidates will be invited to do a self-paced video Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.