06_SettingUpKotlinFramework.md

Shared Kotlin Code for iOS

Let's run the packForXcode Gradle task of the SharedCode project. We can do it either from the Gradle tab in AndroidStudio or by running the ./gradlew :SharedCode:packForXcode command from console. This task is designed to help to simplify the setup of our iOS Framework in the Xcode project model.

We need several binaries from the framework to use it with Xcode:

• iOS arm64 debug to run on the iOS device in debug mode
• iOS arm64 release to include into a release version of an app
• iOS x64 debug for the iOS Simulator, which uses the desktop Mac CPU

The easiest way to configure Xcode to use a custom-built framework is to place the framework under the same folder for all configurations and targets. Then add a custom step to the Xcode project build to update or build the framework before the actual Xcode build is started. Xcode sets several environment variables for custom steps; we can use these variables in the Gradle script to select the requested target platform and the configuration. For more details, please refer to the packForXcode task sources in the SharedCode/build.gradle.kts file.

Let's now switch back to Android Studio and execute the build target of the SharedCode project from the Gradle tool window. The task looks for environment variables set by the Xcode build and copies the right variant of the framework to the SharedCode/build/xcode-frameworks folder. We can then include the framework from that folder into the build

Setting up Xcode

We need to add the SharedCode framework to the Xcode project. To do this we can double-click on the KotlinIOS node (or root node) of the project navigator (⌘1) tree to open the target settings. Next we then click on the + in the Embedded Binaries section, click Add Other... button in the dialog to choose the framework from the disk. We can then point to the following folder:

SharedCode/build/xcode-frameworks/SharedCode.framework

In the next dialog, we need to select the Create folder references option and make sure that the Copy items if needed checkbox isn't checked. We should then see something like this:

Now we need to explain to Xcode, where to look for the framework. For this, we open the Build Settings tab again, pick the All sub-tab below, and type the Framework Search Paths into the search field to find the option easily. We need to add the relative path $(SRCROOT)/../../SharedCode/build/xcode-frameworks to the Search Paths | Framework Search Paths section. Xcode will then show the substituted path in the UI for it.

The final step is to make Xcode call our Gradle build to prepare the SharedCode framework before each run. We can open the Build Phases tab and click + to add the New Run Script Phase, drag that step to the very first position, and add the following code to the shell script text:

cd "$SRCROOT/../../SharedCode/build/xcode-frameworks"
./gradlew :SharedCode:packForXCode -PXCODE_CONFIGURATION=${CONFIGURATION}

Note, here we use the $SRCROOT/../.. as the path to the root of our Gradle project. It can depend on how the Xcode project was created. Also, we use the generated SharedCode/build/xcode-frameworks/gradlew script, the packForXCode task generates it. We assumed that the Gradle build is executed at least once, before opening the Xcode project on a new machine.

The step-007 branch of the github.com/kotlin-hands-on/mpp-ios-android repository contains a possible solution for the tasks that we have done above. We can also download the archive from GitHub directly or check out the repository and select the branch.

We should drag the created build phase to the top of the list

We are now ready to start coding the iOS application with Kotlin

Calling Kotlin Code from Swift

Remember, our goal is to show the text message on the screen. As we see, our iOS application does not draw anything on the screen. Let's make it show the UILabel with the text message. Let's open the ViewController.swift file from the project navigator (⌘1) tree. We need to replace the contents of the ViewController.swift file with the following code:

import UIKit
import SharedCode

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let label = UILabel(frame: CGRect(x: 0, y: 0, width: 300, height: 21))
        label.center = CGPoint(x: 160, y: 285)
        label.textAlignment = .center
        label.font = label.font.withSize(25)
        label.text = CommonKt.createApplicationScreenMessage()
        view.addSubview(label)
    }
}

We use the import SharedCode to import our Framework, which we compiled with Kotlin/Native from Kotlin code. Next, we call the Kotlin function from it as CommonKt.createApplicationScreenMessage(). Follow the Kotlin/Native as an Apple Framework tutorial for more details on the Kotlin/Native to Swift (or Objective-C) interop.

The step-008 branch of the github.com/kotlin-hands-on/mpp-ios-android repository contains a possible solution for the tasks that we have done above. We can also download the archive from GitHub directly or check out the repository and select the branch.

We are now ready to start the application in the simulator or iOS device.

Running the iOS Application

Let's click the Run button in Xcode, and we'll see our application running