Importing a Swift protocol in Objective-C class

Question

I try to import a Swift Protocol named AnalyticProtocol into an Objective-C class named AnalyticFactory.

protocol AnalyticProtocol
         


        

Answer 1

It is not possible to import the Xcode generated Swift header in objC header files.

So, since you want to use Swift code in an objC header file, you will need to "forward declare" the classes and protocols you want to use in the objC header file, like this:

@protocol AnalyticProtocol;

You can now use the protocol in your objC class declaration:

@interface AnalyticFactory : NSObject
{
    Class _analyticProtocolClass; // The type of the analytic class currently used.
}

In your implementation file (the objC .m file), you can import the Xcode generated Swift header ("ProductModuleName-Swift.h") file and the correct implementation AnalyticProtocol will now be known to the compiler.

This is also described in the section "Using Swift from Objective-C" in the Apple Docs

Note that XCode will give a warning in the objC header file when you use the forward declared protocol ("Cannot find protocol definition for 'AnalyticProtocol'), but this is can be ignored - the implementation will be found at compile time.