Swift Mid And Match

Swift’s compatibility with Objective-C lets you create a project that contains files written in either language. You can use this feature, called mix and match, to write apps that have a mixed-language codebase.

To import a set of Objective-C files in the same app target as your Swift code, you rely on an Objective-C bridging header to expose those files to Swift. Xcode offers to create this header file when you add a Swift file to an existing Objective-C app, or an Objective-C file to an existing Swift app.

If you accept, Xcode creates the header file along with the file you were creating, and names it by your product module name followed by adding "-Bridging-Header.h". (You’ll learn more about the product module name later, in Naming Your Product Module.)

Alternatively, you can create a bridging header yourself by choosing File > New > File > (iOS, watchOS, tvOS, or OS X) > Source > Header File.

In your Objective-C bridging header file, import every Objective-C header you want to expose to Swift. For example:

#import "XYZCustomCell.h"

#import "XYZCustomView.h"

#import "XYZCustomViewController.h"

references:
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/BuildingCocoaApps/MixandMatch.html