about iOS target version and SDK version

问题

iOS SDK is upgrading, and some new tech will appear, i.e, block is new tech.

So question is if "block" based implementation also can be distributed to lower target version or older iPhone ( 3G or first generation ) ?

how to cope with those issues ?

回答1:

The usual way to deal with this sort of issue is to selectively enable features at runtime based on the current OS version. However, this can be very complicated to manage.

Query the current OS version at runtime
Use weak linking
Dynamically create the class
Call the new features only if the new class is present

For example:

Class optionalClass = NSClassFromString(@"NSArtificialIntelligence");
if (optionalClass) {
  id optionalObj = [[optionalClass alloc] init];
  // ... 
}

The following documentation describes the process in detail:

Configuring a Project for SDK-Based Development
Using Weakly Linked Classes in iOS

You specifically mention blocks. This feature requires support from the compiler and Objective-C runtime, so it will not be available at all on older systems.

回答2:

You must weak link to libSystem.B.dylib if you are using blocks for iOS4 or later. Because blocks are able to compile with the latest iOS SDK but iOS2,3.0 and 3.1 don't have blocks runtime.

iOS 4 app crashes at startup on iOS 3.1.3: Symbol not found: __NSConcreteStackBlock

(Besides, you can use blocks for iPhone 2.2+. Please take a look at plblocks.)

来源：https://stackoverflow.com/questions/5776313/about-ios-target-version-and-sdk-version

标签

objective-c

ios

objective-c-blocks