How will the project under xcode base sdk version changed from 5.1 to 4.3?

Recent contact with a new project, the development process is always encountered inexplicable bug, was discovered later that sdk version of the problem.


That project development time using xcode_4.0.2, base sdk is 4.3, and my xcode is 4.3.2, the default sdk is 5.1, so I want to configure it to default into xcode 4.3. Tried it, the simulator can be turned into 4.3, but the base sdk only 5.1 unchangeable. To change can only download 4.0.2 version of xcode, it seems, and sdk xcode are bound.


So I let my colleagues gave me pass xcode_4.0.2_and_ios_sdk_4.3.dmg, when prompted during installation, I have to be an operating system os x 10.6.6 job and my current system is 10.7.4, xcode can not be installed. . .


And Baidu a moment found that if I want to change the current system to 10.6, then you have to reinstall the system. . . . .


Which experience some pointers to the younger ah, do not reinstall the system in addition to no other recourse than to the What?
Reply:
Personally do not think the SDK version of the problem, the problem is definitely your code, but you want to change the SDK is also possible, as follows:

Dmg first opened, do not install,
Double / Volumes / Xcode and iOS SDK/Packages/iPhoneSDK4_3.pkg


Reply:
Themselves from the old version of the above the "iPhoneOS4.3.sdk" copy the entire directory to
"/ Developer / Platforms / iPhoneOS.platform / Developer / SDKs /" directory

Restart Xcode 4.3 can change baseSdk it.