Testing 3.x Apps on Phone Running Beta OS

Like many iPhone devs, I have more than one device that I use for testing. I have an iPod Touch that I usually leave at the current release version, an iPad WiFi that I leave at the current release version for the iPad, and I have an iPhone 3Gs that I keep on the bleeding edge beta release version. This way, I have a device to test and run stuff under the beta SDK and under the release SDK, and I keep both installed on my machine so I have the ability to check out and learn the next release of the SDK while still creating applications using the current release of the SDK.

Normally, this is a perfectly sufficient setup for my purposes, but today, it wasn't. I have a problem I'm trying to debug that happens when running on EDGE or on a really slow 3G connection; it never happens under WiFi. I'm doing a fix for a client that will need to go onto the App Store long before 4.0 goes GM, so I need to be working under 3.1.2.

In order to try and reproduce this problem, I have to be able to run the app on my phone because the iPod touch and iPad both only have WiFi connections so, therefore, I can't reproduce the problem there. I don't want to build against the beta SDK because this is a bug fix on an existing app, and the beta install doesn't include the current release SDK that I needs to build under, so I can't build a 3.1.2 app using the beta tools. This is probably done to discourage people from building apps for the App Store with the beta tools (which you really, really shouldn't do). The only problem is, OS versions have to match between the tools and phone, so I can't launch the GM Xcode and and debug apps on my iPhone on which I've installed the beta OS and if I run on my iPod touch, I can't reproduce the problem I need to debug because it doesn't happen under WiFi.

There's actually a solution, which is to create a symbolic link from SDK in the GM tools folder to the beta tools folder. So, in my case, I have GM tools installed at /Developer and the current beta release installed at /DevBeta. In order to compile a 3.1.3 application so I can test it on a phone that's been upgraded to 4.0, I can drop to the terminal and do this:

sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.3.sdk \
/DevBeta/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.3.sdk

If I need to to run and test an application with a base SDK of 3.0 on a phone that's been upgraded to 4.0, instead I do this:

sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.0.sdk \
/DevBeta/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.0.sdk

Do this with Xcode closed, then when you re-open your project with an older base SDK, it should work. All we're doing is creating a symbolic link from the beta tools directory to the appropriate SDK in the GM tool directory.

Now, be aware, this action is likely to be frowned upon by the Mothership; they excluded those SDKs for a reason. But, I haven't disclosed anything about the beta release other than its existence, which is widely known, and there are valid reasons to use the beta tools and the GM SDKs, so I though it worth sharing. Caveat emptor - do this at your own risk and don't get mad at me if it causes problems.