iOS4发布了, 对手上的一个项目用不同版本sdk编译后的兼容性做了下测试:
xcode 3.2.2
Base sdk: iPhone Device 3.1/iPhone Simulator 3.1
iPhone OS Deployment Target: iPhone OS 3.1
compile : Success
MutipleTasks: NO
xcode 3.2.3
Base sdk : iPhone simulater 3.1/ iPhone device 3.1
iPhone OS Deployment Target: iPhone OS 3.1
compile: 38 errors
MutipleTasks: NO
xcode 3.2.3
Base sdk : iPhone simulater 4.0/ iPhone device 4.0
iPhone OS Deployment Target: iPhone OS 3.1
compile: Success
MutipleTasks: YES
xcode 3.2.3
Base sdk : iPhone simulater 4.0/ iPhone device 4.0
iPhone OS Deployment Target: iPhone OS 4.0
compile: Success
MutipleTasks: YES
新版本对旧代码的编译都没问题, 向下兼容性做的很好.