dirmich/iOS-Universal-Framework

An XCode 4 project template to build universal frameworks (arm6, arm7, and simulator) for iOS / iPhone.

iOS Universal Framework Mk 5

An XCode 4 project template to build universal (arm6, arm7, and simulator) frameworks for iOS.

By Karl Stenerud

Why a Framework?

Distributing libraries in a developer-friendly manner is tricky. You need to include not only the library itself, but also any public include files, resources, scripts etc.

Apple's solution to this problem is frameworks, which are basically folders that follow a standard structure to include everything required to use a library. Unfortunately, in disallowing dynamically linked libraries in iOS, Apple also removed static iOS framework creation functionality in XCode.

Xcode is still technically capable of building frameworks for iOS, and with a little tweaking it can be re-enabled.

Static frameworks are perfectly acceptable for packaging code intended for the app store. Despite appearances, it's just a static library at the core.

Kinds of Frameworks

The most common kind of framework is the dynamically linked framework. Only Apple can install these on an iOS device, so there's no point in building them.

A statically linked framework is almost the same, except it gets linked to your binary at compile time, so there's no problem using them.

A fake framework is the result of a hack upon a bundle target in Xcode and some scripting magic. It looks and behaves like a static framework, and a fake framework project is functionally equivalent in most aspects to a real framework project (but not all).

An embedded framework is a wrapper around a static framework, designed to trick Xcode into seeing the framework's resources (images, plists, nibs, etc).

This distribution includes templates to build static frameworks and fake frameworks, as well as embedded framework variants of each.

Choosing Which Template System to Use

In this distribution are two template systems, each with their strengths and weaknesses. You should choose whichever one best suits your needs and constraints (or just install both).

Short decision chart for the impatient

• I can't (or won't) modify my Xcode installation: Fake framework

• I'm just distributing the final framework binary (not the project): Either kind will work

• I'm distributing my framework project to other developers who may not want to modify their Xcode install: Fake framework

• I need to set up the framework project as a dependency of another project (in a workspace or as a child project): Real framework (or Fake framework, using the -framework trick - see below)

• I'm adding static libraries/frameworks to my framework project AND I want them linked into the produced framework so they don't need to be added separately to end-user projects: Fake framework

Fake Framework

The fake framework is based on the well known "relocatable object file" bundle hack, which tricks Xcode into building something that mostly resembles a framework, but is really a bundle.

The fake framework template takes this a step further, using some scripting to generate a real static framework (based on a static library rather than a relocatable object file). However, the framework's project still defines it to be of type 'wrapper.cfbundle', which makes it a second class citizen according to Xcode.

So while it produces a proper static framework that works just as well as a "real" static framework, things get tricky when you have dependencies.

The problem with dependencies

If you're just setting up a standalone project, then you're not using dependencies, so there's no problem.

If, however, you use project dependencies (such as in workspaces), Xcode won't be happy. The fake framework won't show up in the list when you click the '+' button under "Link Binary With Libraries" in your main application project. You can manually drag it from "Products" under your fake framework project, but then when you build your main project, you'll get a warning like this:

warning: skipping file '/somewhere/MyFramework.framework'
(unexpected file type 'wrapper.cfbundle' in Frameworks & Libraries build phase)

This will be followed by linker errors for anything in your fake framework.

Fortunately, there is a workaround. You can manually tell the linker to link in the framework by adding a "-framework" switch with your framework's name in "Other Linker Flags" in the project that uses the framework:

-framework MyFramework

It won't get rid of the warning, which is annoying, but it does link properly.

Adding other static libraries/frameworks

If you add other static (not dynamic) libraries or other static frameworks to your fake framework project, they will be LINKED INTO your final framework binary. In a real framework project they are merely referenced, not linked in.

You can avoid this behavior by only including the header files into your project (so that it will compile), not the static libraries/frameworks themselves.

Real Framework

The real framework is real in every sense of the word. It is a true static framework made by re-introducing specifications that Apple left out of Xcode.

In order to be able to build a real framework project, you must modify Xcode's specification files, which may not be desirable, or even possible due to restrictions your organization may place upon development environments. Also, if you are releasing a project that builds a real framework, anyone who wishes to build that framework must modify their Xcode as well (via the install script in this distribution).

If all you're doing is distributing the fully built framework, and not the framework's project, then the end user doesn't need to modify Xcode.

I've submitted a report to Apple in the hopes that they'll update the specification files in Xcode, but that could take awhile. OpenRadar link here

Adding other static libraries/frameworks

If you add other static (not dynamic) libraries or other static frameworks to your real framework project, they will only be referenced, NOT linked into the final framework binary like they would in a fake framework.

Upgrading from previous iOS-Universal-Framework versions

If you are upgrading from iOS-Universal-Framework Mk 5 or earlier and were using the Real Static Framework, please run "uninstall_legacy.sh" to remove any patches that were previously applied to Xcode.

The new real framework template system uses a cleaner approach to avoid possible conflicts with future versions of Xcode.

Installing the Template System

To install, run the install.sh script in either the "Real Framework" or "Fake Framework" dir (or both).

Now restart Xcode and you'll see Static iOS Framework (or Fake Static iOS Framework) under Framework & Library when creating a new project.

To uninstall, run the uninstall.sh script and restart Xcode.

Creating an iOS Framework Project

1. Start a new project.

2. For the project type, choose Static iOS Framework (or Fake Static iOS Framework), which is under Framework & Library.

3. Optionally choose to include unit tests.

4. Add your classes, resources, etc with your framework as the target.

5. Any header files that need to be available to other projects must be declared public. To do so, go to Build Phases in your framework target, expand Copy Headers, then drag any header files you want to make public from the Project or Private section to the Public section.

Building your iOS Framework

1. Select your framework's scheme (any of its targets will do).

2. (optional) Set the "Run" configuration in the scheme editor (It's set to Debug by default).

3. Build the framework (both "iOS device" and "Simulator" destinations will build the same universal binary, so it doesn't matter which you select).

4. Select your framework under "Products", then show in Finder.

There will be two folders in the build location: (your framework).framework and (your framework).embeddedframework

If your framework has only code, and no resources (like images, scripts, xibs, core data momd files, etc), you can distribute (your framework).framework to your users and it will just work.

If you have included resources in your framework, you MUST distribute (your framework).embeddedframework.

Why is an embedded framework necessary? Because XCode won't look inside static frameworks to find resources, so if you distribute (your framework).framework, none of its resources will be visible or usable.

An embedded framework is simply an extra wrapper around a framework, containing symbolic links to the framework's resources. Doing this makes Xcode happy-warm-and-fuzzy because it can finally see the resources.

Using an iOS Framework

iOS frameworks are basically the same as regular dynamic Mac OS X frameworks, except they are statically linked.

To add a framework to your project, simply drag it into your project. When including headers from your framework, remember to use angle bracket syntax rather than quotes.

For example, with framework "MyFramework":

#import <MyFramework/MyClass.h>

Troubleshooting

Headers Not Found

If Xcode can't find the header files from your framework, you've likely forgotten to make them public. See step 5 in Creating an iOS Framework Project

No Such Product Type

If someone who has not installed iOS Universal Framework in their development environment attempts to build a universal framework project (for a real framework, not a fake framework), they'll get the following error:

target specifies product type 'com.apple.product-type.framework.static',
but there's no such product type for the 'iphonesimulator' platform

Xcode requires some modification in order to be able to build true iOS static frameworks (see the two diff files in the "Real Framework" folder of this repository for the gory details), so please install it on all development machines that will build your real static framework projects (this isn't needed for users of your framework, only for builders of the framework).

The selected run destination is not valid for this action

Sometimes Xcode gets confused and loads the wrong active settings. The first thing to try is restarting Xcode. If it still fails, Xcode generated a bad project (this can happen with any kind of project due to a bug in Xcode 4). If this happens, you'll need to start over and create a new project.

Linker Warnings

The first time you build your framework target, XCode may complain about missing folders during the linking phase:

ld: warning: directory not found for option
'-L/Users/myself/Library/Developer/Xcode/DerivedData/MyFramework-ccahfoccjqiognaqraesrxdyqcne/Build/Products/Debug-iphoneos'

If this happens, simply clean and rebuild the target and the warnings should go away.

Core Data momd not found

Xcode builds managed object model files differently in a framework project than it does in an application project. Instead of creating a .momd directory containing VersionInfo.plist and the .mom file, it simply creates the .mom file in the root directory.

This means that when initializing your NSManagedObjectModel from a model in an embedded framework, you must specify your model URL with an extension of "mom" rather than "momd":

NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"MyModel" withExtension:@"mom"];

Unknown class MyClass in Interface Builder file.

Since static frameworks are statically linked, the linker strips out any code it thinks is not being used. Unfortunately, the linker does not check xib files, and so if a class is referenced only in a xib, and not in objective-c code, the linker will drop that class from the final executable. This is a linker issue, not a framework issue (it also happens when you build a static library).

Apple's built-in framworks don't suffer this problem because they are dynamically loaded at runtime and the complete, unstripped dynamic library exists in the iOS device's firmware.

There are two ways around this:

1. Have end users of your framework disable linker optimizations by adding "-ObjC" and "-all_load" to "Other Linker Flags" in their project.

2. Put a code reference to the class inside another class in your framework that always gets used. For example, suppose you have "MyTextField", which is getting stripped by the linker. Suppose you also have "MyViewController", which uses MyTextField in its xib file and doesn't get stripped. You could do the following:

In MyTextField:

+ (void) forceLinkerLoad_ {}

In MyViewController:

+ (void) initialize
{
    [super initialize];
    [MyTextField forceLinkerLoad_];
}

Option 2 is more work for you, but if done right it saves the end user from having to disable linker optimizations just to use your framework.

unexpected file type 'wrapper.cfbundle' in Frameworks & Libraries build phase

This happens when you use a fake framework project as a dependency in a workspace, or as a child project (real framework projects don't have this issue). Even though the framework project produces a proper static framework, Xcode only looks at the project file, which says it's a bundle, and so it issues a warning during the dependency check and then skips it during the linker phase.

You can get it to link properly by manually adding a command to link your framework during the linker phase. Add a command to link your framework in "Other Linker Flags" in the project that depends on the framework:

-framework MyFramework

You'll still get the warning, but it won't fail in the linker phase anymore.

Libraries being linked or not being linked into the final framework

Unfortunately, due to the way Xcode works, the "Real Framework" and "Fake Framework" templates handle included static libraries/frameworks differently.

The "Real Framework" template follows correct static library procedure, NOT linking other static libraries/frameworks into the final product.

The "Fake Framework" template tricks Xcode into thinking that it's building a relocatable object file, and so the linking phase treats it as if it were building an executable, linking all static code sources into the final binary (although it doesn't check for missing object code). To get the "Real Framework" behavior, you should include only the header files from the library/framework in your framework project, not the static library or framework itself.

Unrecognized selector in (some class with a category method)

If your static library or static framework contains a module with ONLY category code (no full class implementations), the linker will get confused, and will leave the code out of the final binary. Since it's not present in the final product, you'll get "unrecognized selector" exceptions when any call is made to those category methods.

To get around this, put a dummy class into the module containing the category code. The linker, seeing a full Objective-C class, will link the module in, including the category code.

I've made a header file LoadableCategory.h to make this easier to do:

#import "SomeConcreteClass+MyAdditions.h"
#import "LoadableCategory.h"


MAKE_CATEGORIES_LOADABLE(SomeConcreteClass_MyAdditions);


@implementation SomeConcreteClass (MyAdditions)

...

@end

You will also need to add "-ObjC" to the "Other Linker Flags" build setting in any project that uses the framework.

History

Mk 1

The first incarnation. It used a bunch of script hackery to cobble together a fake framework. It exploited the "bundle" target, setting its type to a relocatable object file.

Mk 2

This version took advantage of the template system to do most of the work that the script used to do. Everything (including the script) was embedded in the template.

Mk 3

This version does away with the "relocatable object" hackery and builds a true static framework, with all the abilities of an OS X static framework. This solves a number of linker, unit testing, and workspace inclusion issues that plagued the previous hacky implementations.

It also includes the concept of the embeddedframework, which allows you to include resources with your framework in a way that Xcode understands.

Josh Weinberg also added some tweaks to make it build in the proper build directory with scheme-controlled configuration, and behave better as a subproject dependency.

It now requires some small modifications to Xcode's specification files in order to support true static frameworks, and thus comes with an install and uninstall script.

Mk 4

This version gives you the choice of installing the "real framework" template or the "fake framework" template. Both come with an install script, but only the "real framework" installer needs to modify Xcode.

This also fixes some issues that the fake framework had in Mk 2 (such as the curious behavior of embedding the full path to the compiled files within the files themselves, resulting in warnings when building with that framework).

Mk 5

This version does away with the extra target and script. Everything is self contained in the framework target, and the framework under the "Products" group is actually the universal framework (no more Debug-univesal or Release-universal folders).

You can build and clean like you would in any other project.

As well, the "Fake" framework template now builds a proper static library instead of a relocatable object file (although Xcode still doesn't believe that it's real).

Mk 6

This version makes the Xcode modifications for real static frameworks safer by simply adding an extra specification file instead of patching existing ones.

Users upgrading from Mk 3, Mk 4, or Mk 5 can run "uninstall_legacy.sh" to unpatch Xcode.

License

Copyright (c) 2011 Karl Stenerud

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in the documentation of any redistributions of the template files themselves (but not in projects built using the templates).

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.