问题
I wanted to ask how compatibility on different iOS operation systems works in iOS. For example If I develop an app on Xcode 9.2 and Swift 4 for iOS 11, should it work on iOS 9?
I am coming from Android background which you specify the minimum Android OS that is needed for the app to run in the Gradle file. Does anything similar exist on iOS?
回答1:
Very simple solution:
Set deployment target as 9.0 in your build target general settings. iOS will automatically handle support from 9.0 onwards for a build (your app).
Your app/build will be allowed to use/import frameworks and other libraries, compatible to minimum deployment target, only.
More detail about App Deployment Target from Apple.
回答2:
Please set your deployment target to 9.0
回答3:
Yes, it will work on iOS9 With Xcode 9.2 and swift4 you can develop an application for ios8.0 and above.
In your project setting, you have to select your development target
回答4:
Yes, there is backward compatibility, but for older iOSes you have to check version when using newer API. Luckily we've got availability attributes (@available)
If you want to know HOW it works, basically for Swift your application has its own swift standard library embedded into binary of your application. In case of Objective C – newer iOSes keep sdk's of older versions to maintain backward compatibility.
来源：https://stackoverflow.com/questions/48337125/ios-compatibility-on-different-ios-operation-systems