Swift 2.0 and Objective C in a Mixed Project

Example code on how to use Objective C and Swift components together in a project. Use cases:

• Invoking Objective C classes from Swift
  • In the same project
  • Unit testing Objective C classes from Swift
• Invoking Swift classes from Objective C
  • In the same project
  • Unit testing Swift classes from Objective C

Why

Since the announcement of Swift it has been possible to use Objective C and Swift code together in the same project. However even with XCode 7, using the two languages together is not very straightforward and the Apple documentation doesn't provide a working example to demonstrate this usage.

This sample makes it easy to get started. It also serves as a guide on using Swift 2.0 and Objective C together in applications for XCode 7.0 upwards.

Invoking Objective C code from Swift

• Add the Objective C header file to the Bridging header
• E.g. in the MixedLanguageExample project e.g. to use the ComponentObjectiveC class from any Swift file in the project
  • In MixedLanguageExample/MixedLanugageExample-Bridging-Header.h add

  #import "ComponentObjectiveC.h"
  

  • After this ComponentObjectiveC can be used in any Swift file within the MixedLanguageExample project (e.g. as used in LabelSwift.swift)

Unit testing Objective C classes from Swift

• Import Objective C classes to test via the test target's bridging header.
• E.g. to test the ComponentObjectiveC Objective C class from ComponentObjectiveCFromSwiftTests.swift:
  • In the unit test file MixedLanugageExampleTests / MixedLanugageExampleTests-Bridging-Header.h
  • import the Objective C header file

  #import "ComponentObjectiveC.h"
  

Invoking Swift code from Objective C

• Import the XCode generated header file to use it in the .m file
• E.g. in the MixedLanguageExample to use the ComponentSwift class from LabelObjectiveC:
  • Make sure for the main target, under Build Settings --> Defines Module is set to Yes
  • In LabelObjectiveC.m add

  #import "MixedLanugageExample-Swift.h"
  

Unit Testing Swift classes from Objective C

• Make sure for the test target (in the example, MixedLanugageExampleTests), under Build Settings --> Defines Module is set to Yes
• Import the XCode generated header file in unit tests:
  • E.g. in ComponentSwiftFromObjectiveCTests.m
  • Import the XCode genrated header file for the test target by adding

  #import "MixedLanugageExampleTests-Swift.h"
  

FAQ

• Q: What about working with Swift 1.0 using XCode 6.xx?

  A: The steps are exactly the same. I created the sample using XCode 7.0 beta as it has better Swift support (even if the beta is unstable)

• Q: When testing Objective C classes using Swift, do I need to re-import the Objective C header files in the bridging header, in my test project? I've already done this in my production project.

  A: Seems like this is the only way to do it. Think of the bridging header as the new prefix header for Swift to work with Objective C.