How to Use iPhone 3.0 Features and Still Run on 2.2

iPhone SDK 3.0 has a lot of nifty new features.  One feature I want to use is to send email without exiting my application.  In the past, I have to use UIApplication openURL: to launch the Mail application.  But once I do that, the user is gone, gone, gone.

In SDK 3.0, there is a MFMailComposeViewController class that allows me to bring up a Mail Composer view.  When the user is done with the email and tap Send, user is back in my application.  Can it be cooler than that?

Yes, of course.  Using the MFMailComposeViewController class, I can also preload the body with an attachment.  So, if my application generates a graphical chart, a CSV file, a sound file, etc., I can attach it to the email that is being sent.

The MailComposer sample application (you may need to be logged into Apple’s Developer Connection to access this link) goes into the nitty gritty details on how to use this new class.  Definitely dig into the sample code.

My first question was does that mean that my application is now limited to iPhone OS 3.0 users?  I don’t want to do that as it excludes a large segment of the population who did not bother to upgrade (even though the upgrade is free on the iPhone).  Here’s the cool part.  You don’t have to exclude the pre-3.0 users.  The MailComposer sample application goes into the details of how to do that.

1. You build the application with SDK 3.0.
2. You target to iPhone OS 2.2.1 (or whatever version you want).
3. You write your code to check for existence of certain 3.0 framework before using them, and provide a graceful degradation path for pre-3.0 users.
4. In setting up the Frameworks for your build target, you set the role of the 3.0 framework used in your application to weak such that application will launch even if some of the frameworks are missing.

Step 4 above is the important part.  If you don’t do that, your application will fail to launch on pre-3.0 devices.  The following is the screen capture for where to set a framework’s role to weak.

Xcode example of where to set a Framework to Weak

As for testing, if you have the luxury of a rackful of devices running different OSes, by all means test on all of them.  The other option is to test on pre-3.0 OSes using the iPhone Simulator.  The way to do that is first build and test by setting Xcode to Simulator 3.0 setting.  This leaves a 3.0 version on your iPhone Simulator. Then from the iPhone Simulator men, choose Hardware > Version and select 2.2.1.  Then launch your 3.0 application in a 2.2.1 environment and test away.