An Xcode 4 project template to create universal (armv6, armv7 and simulator) static libraries for iOS.
The existing static library template provided with Xcode only builds one architecture, which is not particularly suitable for distribution. A number of people have created scripts to create universal libraries, which require some mucking around with Xcode target settings to use.
This template draws on this work to provide all that is required to produce universal libraries - just select the 'Universal Static Library' type in the New Project/New Target dialog, and you're all set.
Copy the Universal Static Library.xctemplate folder into ~/Library/Developer/Xcode/Templates/Framework & Library
Sorted.
After the build process finishes, you'll be left with a static library with all three architectures (armv6, armv7, i386) - you can verify this by opening up the terminal and typing file {path to library}.
The build script automatically copies the universal product (from the "Release-universal" or "Debug-universal" folders in the built products dir) back over the original single-architecture build, so you'll find the same universal version in each of the build folders.
Frameworks are Apple's solution to the inconvenience of distributing and handling static libraries and their accompanying headers (which requires setting header search paths, etc.)
Karl Stenerud has created a fantastic set of Xcode templates for universal iOS frameworks.
These will probably work just fine for many people, but we have recently discovered that LLVM appears to have a linking bug that causes unpredictable crashes when calling C functions within the static framework. Frameworks that work fine in one app may crash in another app, without warning.
Consequently, if you are using C functions within your library, I recommend that you avoid frameworks for now and use a static library instead.
Build script by Adam Martin
Tweaked and made into an Xcode template by Michael Tyson
Based on original script from Eonil
More info: see this Stack Overflow question