How is Swift code integrated into an Objective-C project?

Integration of Swift code into an Objective-C project is done using the so-called "Bridging Header" and the automatically generated file ProjectName-Swift.h.

Main steps:

1. In your Objective-C project, add a Swift file. Xcode will suggest creating a Bridging Header — it is needed for reverse integration of Objective-C into Swift, but for calling Swift from Objective-C, it is not mandatory.

2. To call Swift from Objective-C, use the automatically generated header file ProjectName-Swift.h. You do not need to create it manually; Xcode generates it.

3. In your Objective-C files, import this header:

#import "ProjectName-Swift.h"

4. Now you can use public Swift classes and methods in Objective-C.

Important:

• Swift classes should be declared with the @objc modifier or inherit from NSObject to be visible in Objective-C.

Example of a Swift class:

@objc class MySwiftClass: NSObject {
    @objc func greet() -> String {
        return "Hello from Swift!"
    }
}

In Objective-C:

MySwiftClass *obj = [[MySwiftClass alloc] init];
NSLog(@"%@", [obj greet]);