KMP Android/iOS UI Alert (Toast/Alert dialog). Does not require Compose. Uses androidx.startup on Android, but this can be avoided by manually accessing Context or by marking the function as @composable and using LocalContext.current

androidApp...AndroidManifest.xml

<application  
        ...
        <provider
            android:name="androidx.startup.InitializationProvider"
            android:authorities="${applicationId}.androidx-startup"
            android:exported="false"
            tools:node="merge">
            <meta-data
                android:name="<package-name>.AndroidApplicationContextInitializer"
                android:value="androidx.startup"/>
        </provider>
    </application>

androidMain...ShowAlert.android.kt

import kotlin.properties.Delegates
import android.app.Application
import android.content.Context
import android.widget.Toast
import androidx.startup.Initializer

actual fun showUIAlert(message: String) {
    Toast.makeText(
        AndroidApplicationContext.application,
        message,
        Toast.LENGTH_SHORT,
    ).show()
}

internal class AndroidApplicationContextInitializer : Initializer<Context> {
    override fun create(context: Context): Application {
        AndroidApplicationContext.setUp(context.applicationContext as Application)
        return AndroidApplicationContext.application
    }
    
    override fun dependencies(): List<Class<out Initializer<*>>> = emptyList()
}

internal object AndroidApplicationContext {
    var application by Delegates.notNull<Application>()
        private set
    
    fun setUp(application: Application) {
        this.application = application
    }
}

commonMain...ShowAlert.kt

expect fun showUIAlert(message: String)

iosMain...ShowAlert.ios.kt

import platform.Foundation.NSLog
import platform.Foundation.NSTimer
import platform.UIKit.UIAlertAction
import platform.UIKit.UIAlertActionStyleDefault
import platform.UIKit.UIAlertController
import platform.UIKit.UIAlertControllerStyleAlert
import platform.UIKit.UIApplication
import platform.UIKit.UIDevice
import platform.darwin.dispatch_async
import platform.darwin.dispatch_get_main_queue

actual fun showUIAlert(message: String) {
    val viewController = UIApplication.sharedApplication.keyWindow?.rootViewController
    if (viewController != null) {
        val alertController = UIAlertController.alertControllerWithTitle(
            title = UIDevice.currentDevice.systemName,
            message = message,
            preferredStyle = UIAlertControllerStyleAlert,
        )
        alertController.addAction(
            UIAlertAction.actionWithTitle(
                "OK",
                style = UIAlertActionStyleDefault,
                handler = null,
            ),
        )
        
        dispatch_async(dispatch_get_main_queue()) {
            viewController.presentViewController(
                viewControllerToPresent = alertController,
                animated = true,
                completion = {
                    val delay = 1.5
                    NSTimer.scheduledTimerWithTimeInterval(delay, repeats = false) {
                        alertController.dismissViewControllerAnimated(true, completion = null)
                    }
                },
            )
        }
    } else {
        NSLog("Error: rootViewController is null")
    }
}

KMP Android and iOS UI Alert

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