Can Blocks built for the iPhone 4 SDK work when deployed to iPhone OS 3.0?

The latest Xcode IDE requires you to target iPhone SDK 4 while dynamically handling deprecated and new functionality if you set the application to deploy to earlier releases.

So can I use new features like Blocks and still have it work on a device running iPhone OS 3.0 or 3.1 or 3.1.3?

I have not found documentation on how to do backward compatibility for previous iPhone OS versions. If you could point me to official docs which cover how this should be d开发者_开发百科one I'd appreciate it.

As far as I know, blocks won't work pre-3.2 because the Blocks runtime is not included (classes like __NSStackBlock__ or whatever). Other than that, my understanding is that you can compile code with blocks if you use a new enough compiler. A solution would be to include a custom blocks runtime conditionally with your project.

While the easiest thing to do is try it, I think that they wont cause harm if present but not used (eg. you use a runtime if statement to circumvent the blocks using code on pre-4.0 devices), but they will certainly not run on pre-4.0 devices, and all of the APIs Apple provides that use blocks will be unavailable anyway. All in all, if you have a way to do something without blocks, there is no reason to have a different way to do it with blocks -- this just increases redundancies and duplicated code -- therefore if you wish to target pre-4.0 devices, you should not use blocks, but if you want/need to use blocks, don't target OSes below 4.0

Use preprocessor directives (http://developer.apple.com/iphone/library/documentation/xcode/conceptual/iphone_development/115-Configuring_Applications/configuring_applications.html) such as TARGET_OS_IPHONE to use code for different iOS versions.

No, blocks won't work on iPhone pre-3.2 without PLBlocks — and even then, whatever method is taking the block might not exist.