The skip-bluetooth framework is available at https://github.com/skiptools/skip-bluetooth.git, which can be checked out and tested with skip test once Skip is installed.

SkipBluetooth

• Implementation Instructions
  • Asking for Permissions
• Building
• Testing

This is a free Skip Swift/Kotlin library project containing the following modules:

Implementation Instructions

SkipBluetooth aims to provide API parity to CoreBluetooth, but in a few cases, this requires using // SKIP DECLARE: in your implementation.

There are delegate methods which have the same argument type signature (despite having differently-named parameters) in CoreBluetooth, and are therefore recognized as the same function to gradle since Kotlin doesn’t differentiate between function calls based on parameter names. One such collision example is:

func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral)
func centralManager(central: CBCentralManager, DidUpdateANCSAuthorizationFor peripheral: CBPeripheral)

In order to implement these functions in your CBCentralManagerDelegate implementation, you should write the function call as you would do in Swift, but put the corresponding // SKIP DECLARE: ... line above that function which corresponds to the Kotlin-compliant API call.

Here is an example:

/* Assuming this function is inside of a class conforming to `CBCentralManagerDelegate` */

// SKIP DECLARE: override fun centralManagerDidConnect(central: CBCentralManager, didConnect: CBPeripheral)
func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
    /* Your implementation here */
}

Here is a list of all such currently-available functions and their corresponding calls:

CBCentralManagerDelegate

CBPeripheralManagerDelegate

CBPeripheralDelegate

Asking for Permissions

Bluetooth requires permissions for both IOS and Kotlin, so you must add the following to your Info.plist file:

• NSBluetoothAlwaysUsageDescription

and these to your AndroidManifest.xml

<manifest>
    <!-- What you need generally -->
    <uses-permission android:name="android.permission.BLUETOOTH" />

    <!-- Allows elevated privileges (like turning on and off on android) -->
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

    <!-- If you want central privileges

    Because you can use bluetooth to discern the user's fine-grained location, you can use this attribute
    to assure that you don't need bluetooth for their location (or remove it and signal your use in the converse)
    -->
    <uses-permission android:name="android.permission.BLUETOOTH_SCAN" android:usesPermissionFlags="neverForLocation" />

    <!-- If you want peripheral privileges -->
    <uses-permission android:name="android.permission.BLUETOOTH_ADVERTISE" />

    <!-- If you want to connect in either case -->
    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
    <!-- other properties -->
</manifest>

[!IMPORTANT] You must request runtime permissions in an #IF SKIP block to prevent your app from crashing

Before using any Bluetooth API’s, you must request user permissions in the body of the view or function which will use Bluetooth.

An example:

import SwiftUI

#if SKIP
import SkipBluetooth
import androidx.compose.runtime.Composable
import androidx.compose.runtime.SideEffect
import androidx.activity.compose.rememberLauncherForActivityResult
import androidx.activity.result.contract.ActivityResultContracts
#endif

struct ContentView: View {
    var body: some View {
#if SKIP
    askForBluetoothPermissions()
#endif
    }
}

/// Prompts the user to allow bluetooth permissions
@Composable
public func askForBluetoothPermissions() {
    let requestPermissionLauncher = rememberLauncherForActivityResult(contract = ActivityResultContracts.RequestMultiplePermissions()) { perms in
        // Handle permissions here if you'd like
    }

    let permissions: kotlin.Array<String> = kotlin.arrayOf(
        Manifest.permission.BLUETOOTH_SCAN,
        Manifest.permission.BLUETOOTH_CONNECT
    )

    // Skip can't implicitly convert between kotlin.Array<string> and
    // skip.lib.Array<String> hence the cast
    SideEffect {
        requestPermissionLauncher.launch(permissions)
    }
}
#endif

This will request Bluetooth permissions as soon as the view appears. Subsequent loads of this view will not show the prompt again—you will have to request the user to enable Bluetooth in settings if they denied permission previously.

There may be a better implementation which automatically shows this prompt when CBCentralManager or CBPeripheralManager are instantiated as is done in CoreBluetooth

Building

This project is a free Swift Package Manager module that uses the Skip plugin to transpile Swift into Kotlin.

Building the module requires that Skip be installed using Homebrew with brew install skiptools/skip/skip. This will also install the necessary build prerequisites: Kotlin, Gradle, and the Android build tools.

Testing

The module can be tested using the standard swift test command or by running the test target for the macOS destination in Xcode, which will run the Swift tests as well as the transpiled Kotlin JUnit tests in the Robolectric Android simulation environment.

Parity testing can be performed with skip test, which will output a table of the test results for both platforms.