Monday, November 17, 2008

Building static libraries with the iPhone SDK

I have a client that wants to use my iPhone Radio Player code for their own radio station, however they want to be able to submit the app to iTunes under their own developer account. The gotcha is they are not purchasing my source code - they want to pay a smaller fee and just have me supply them with a binary image which they can then submit to Apple.

I do not have access to my client's Apple developer account, so I needed a way to supply the client with an Xcode project that includes a skeleton of source code along with a binary library that includes all the custom radio player functionality I have developed. This will allow the client to build the iPhone app and submit it via their account without giving the client access to my source code. Normally, one would probably create a custom framework to wrap up the custom radio player code, but in the case of the iPhone, this is not an option. Apple forbids the use of external frameworks or dynamic library linking in an iPhone app. Instead, I needed to create a static library containing my radio player code.

Fortunately, creating a static library for the iPhone turned out to be a fairly simple, but not at all well documented, process. If you already have an Xcode project, you can easily turn any portion of the source code into a static library. Here's how.

1) In your Xcode project, locate the "Targets" section under the "Groups & Files" sidebar. Right click on "Targets" and choose to add a new target:

Then, in the following dialog box that appears, choose a Cocoa Touch "Static Library" target:

Name the library whatever you'd like. In this example, I named the library "TestStaticLib."

2) Now, assign source code files to your static library. You can simply drag existing files from your project list. Note: don't add the .h files.

3) Then, remove those same source code files from your app target:

4) Add the new static library to your target app via the "General" settings for the target:

5) Edit your target app's linking settings to add "-ObjC" to the "Other Linker Flags". This is only required if your static library defines Objective-C classes that your app is going to reference:

6) Build your new static library for all the SDK targets (such as simulator, iPhone Device, etc.).

7) Build your app. It should now be referencing the static library rather than compiling from the original source code.

If you need to then distribute the app to a client, you can simply remove the source code for the static library and the client will still be able to build the app without having access to the original source code.

This technique might also be useful if you have some shared code you'll use in multiple applications, but don't want to recompile the shared code each time you make a new app that references it. Simply copy the shared library binary images to a specific location in your development environment and then have all your apps link with that code.

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