I was given a task to convert an existing android app so it works on iOS using kotlin multiplatform. I will mention that I am very green in this area and not experienced at all, so I would highly appreciate guidance. After creating the shared module and fidgeting with the build.gradle files I finally got the project to build, however once I moved a java file from androidApp module to the shared module and converted it to a kotlin file, every import and further code throws an unresolved reference error. For example I have this file that was originaly in java:

import android.content.Intent;
import android.util.Log;

import com.google.firebase.iid.FirebaseInstanceId;
import com.google.firebase.iid.FirebaseInstanceIdService;

public class FbInstanceIdService extends FirebaseInstanceIdService{

    public static final String TAG = "FirebaseID";
    public static final String TOKEN_BROADCAST = "tokenbroadcast";


    @Override
    public void onTokenRefresh() {
        // Get updated InstanceID token.
        String refreshedToken = FirebaseInstanceId.getInstance().getToken();
        Log.d(TAG, "Refreshed token: " + refreshedToken);

        // If you want to send messages to this application instance or
        // manage this apps subscriptions on the server side, send the
        // Instance ID token to your app server.

        getApplicationContext().sendBroadcast(new Intent(TOKEN_BROADCAST));
        storeToken(refreshedToken);
    }

    private void storeToken(String token){
        SharedPreferencesManager.getInstance((getApplicationContext())).storeFirebaseToken(token);
    }
}

This is the same code converted to kotlin:

package eu.tinysolutions.tinyprocas

import android.content.Intent
import android.util.Log
import com.google.firebase.iid.FirebaseInstanceId
import com.google.firebase.iid.FirebaseInstanceIdService


class FbInstanceIdService : FirebaseInstanceIdService() {
    fun onTokenRefresh() {
        // Get updated InstanceID token.
        val refreshedToken: String = FirebaseInstanceId.getInstance().getToken()
        android.util.Log.d(
            TAG,
            "Refreshed token: $refreshedToken"
        )

        // If you want to send messages to this application instance or
        // manage this apps subscriptions on the server side, send the
        // Instance ID token to your app server.
        getApplicationContext().sendBroadcast(Intent(TOKEN_BROADCAST))
        storeToken(refreshedToken)
    }

    private fun storeToken(token: String) {
        SharedPreferencesManager.getInstance(getApplicationContext()).storeFirebaseToken(token)
    }

    companion object {
        const val TAG = "FirebaseID"
        const val TOKEN_BROADCAST = "tokenbroadcast"
    }
}

I got errors like these:
Unresolved reference: content
Unresolved reference: util
Unresolved reference: FirebaseInstanceId
Unresolved reference: FirebaseInstanceIdService
Unresolved reference: getApplicationContext
and so on…

There are a ton more files but everywhere the errors remain similar.

I mostly tried changing the build.gradle files, however no errors were solved. I will post them in case they do help solve the problem.

Project level build.gradle file:

// Top-level build file where you can add configuration options common to all sub-projects/modules.


buildscript {
    
    repositories {
        google()
        jcenter()
        mavenCentral()
    }
    dependencies {
        classpath('com.android.tools.build:gradle:8.1.4')
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.9.0"

        classpath 'com.google.gms:google-services:4.4.1'
    }
}

plugins {
    // Declare the Kotlin Multiplatform plugin with a specific version and set apply false
    id 'org.jetbrains.kotlin.multiplatform' version '1.9.0' apply false
    id 'com.android.application' version '8.1.4' apply false
    id 'com.android.library' version '8.1.4' apply false
    id("com.google.gms.google-services") version "4.4.1" apply false

}

allprojects {
    repositories {
        google()
        jcenter()
        mavenCentral()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

androidApp build.gradle file:

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'

android {
    compileSdk 27
    defaultConfig {
        applicationId "changedID"
        minSdkVersion 26
        targetSdkVersion 27
        versionCode 11
        versionName "1.11"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    applicationVariants.all { variant ->
        variant.resValue "string", "versionName", variant.versionName
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    namespace 'changedNamespace'
}

repositories {
    maven { url 'https://jitpack.io' }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:27.1.1'
    implementation 'com.android.support.constraint:constraint-layout:1.1.1'
    implementation 'com.android.support:support-v4:27.1.1'
    implementation 'com.google.firebase:firebase-messaging:11.8.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation 'com.android.support:support-v4:27.1.1'
    implementation 'com.android.support:design:27.1.1'
    implementation 'com.android.volley:volley:1.1.0'
    implementation 'com.ms-square:expandableTextView:0.1.4'
    implementation project(':shared')
    implementation 'com.github.PhilJay:MPAndroidChart:v3.0.3'
}

apply plugin: 'com.google.gms.google-services'

shared module build.gradle.kts file:

plugins {
    //alias(libs.plugins.kotlinMultiplatform)
    //alias(libs.plugins.androidLibrary)
    //alias(libs.plugins.androidApplication)
    id("org.jetbrains.kotlin.multiplatform")
    id("com.android.application")
    id("com.google.gms.google-services")
}

repositories {
    maven(url = "https://jitpack.io")
}


kotlin {
    androidTarget {
        compilations.all {
            kotlinOptions {
                jvmTarget = "1.8"
            }
        }
    }
    
    listOf(
        iosX64(),
        iosArm64(),
        iosSimulatorArm64()
    ).forEach {
        it.binaries.framework {
            baseName = "shared"
            isStatic = true
        }
    }

    sourceSets {
        val commonMain by getting {
            dependencies {
                implementation(fileTree(mapOf("dir" to "libs", "include" to listOf("*.jar"))))
                implementation(project(":shared"))
                implementation ("com.android.support:appcompat-v7:27.1.1")
                implementation ("com.android.support.constraint:constraint-layout:1.1.1")
                implementation ("com.android.support:support-v4:27.1.1")
                implementation ("com.google.firebase:firebase-messaging:11.8.0")
                implementation ("com.android.support:support-v4:27.1.1")
                implementation ("com.android.support:design:27.1.1")
                implementation ("com.android.volley:volley:1.1.0")
                implementation ("com.ms-square:expandableTextView:0.1.4")
                implementation ("com.github.PhilJay:MPAndroidChart:v3.0.3")
            }
        }
        val androidMain by getting{
            dependencies{
                implementation(fileTree(mapOf("dir" to "libs", "include" to listOf("*.jar"))))
                implementation(project(":shared"))
                implementation ("com.android.support:appcompat-v7:27.1.1")
                implementation ("com.android.support.constraint:constraint-layout:1.1.1")
                implementation ("com.android.support:support-v4:27.1.1")
                implementation ("com.google.firebase:firebase-messaging:11.8.0")
                implementation ("com.android.support:support-v4:27.1.1")
                implementation ("com.android.support:design:27.1.1")
                implementation ("com.android.volley:volley:1.1.0")
                implementation ("com.ms-square:expandableTextView:0.1.4")
                implementation ("com.github.PhilJay:MPAndroidChart:v3.0.3")
            }
        }
        val commonTest by getting {
            dependencies {
                implementation(kotlin("test-common"))
                implementation(kotlin("test-annotations-common"))
            }
        }

        // Specific platform configurations
        val iosX64Main by getting {
            dependsOn(commonMain)
        }
        val iosArm64Main by getting {
            dependsOn(commonMain)
        }
        val iosSimulatorArm64Main by getting {
            dependsOn(commonMain)
        }
    }
}

android {
    namespace = "changedNamespace"
    compileSdk = 27
    defaultConfig {
        minSdk = 26
        applicationId = "changedID"
        versionCode = 11
        versionName = "1.11"
        targetSdk = 27
    }
}