Android Development dengan Kotlin

// ===== VARIABEL =====
val nama: String = "BeebaneLabs"   // Immutable (tidak bisa diubah)
var umur: Int = 25                  // Mutable (bisa diubah)

// Type inference — tipe di-inferensi otomatis
val kota = "Jakarta"               // String
val populasi = 10_000_000          // Int (underscore untuk readability)
val tinggi = 175.5                  // Double
val isActive = true                 // Boolean

// Nullable types
var alamat: String? = null          // Bisa null dengan ?
var namaLengkap: String = "Budi"    // Tidak bisa null

// Safe call operator ?. dan Elvis operator ?:
val panjang = alamat?.length ?: 0   // Jika null, hasilnya 0

// ===== TIPE DATA DASAR =====
val angka: Byte = 127               // 8-bit
val angka2: Short = 32767           // 16-bit
val angka3: Int = 2147483647        // 32-bit
val angka4: Long = 9_223_372_036_854_775_807  // 64-bit
val desimal: Float = 3.14f          // 32-bit
val desimal2: Double = 3.14159265   // 64-bit
val huruf: Char = 'A'               // Single character
val teks: String = "Hello Kotlin"   // String

// Function biasa
fun tambah(a: Int, b: Int): Int {
    return a + b
}

// Single-expression function
fun kali(a: Int, b: Int): Int = a * b

// Default parameters & named arguments
fun sapa(nama: String, pesan: String = "Halo"): String {
    return "$pesan, $nama!"
}
// sapa("Budi")              → "Halo, Budi!"
// sapa("Budi", pesan="Hey") → "Hey, Budi!"

// Extension function
fun String.kebalikan(): String = this.reversed()
// "Hello".kebalikan() → "olleH"

// Lambda
val kuadrat = { x: Int -> x * x }
val list = listOf(1, 2, 3, 4, 5)
val genap = list.filter { it % 2 == 0 }
val hasil = list.map { it * 2 }

// Higher-order function
fun operasi(a: Int, b: Int, op: (Int, Int) -> Int): Int {
    return op(a, b)
}
val hasilTambah = operasi(5, 3) { x, y -> x + y }

// Coroutines — async
suspend fun fetchData(): String {
    delay(1000)  // Non-blocking delay
    return "Data dari server"
}

// Class biasa
class Mahasiswa(val nama: String, var umur: Int) {
    var jurusan: String = "Teknik Informatika"

    init {
        println("Mahasiswa $nama dibuat")
    }

    fun perkenalkan() {
        println("Halo, saya $nama, umur $umur, jurusan $jurusan")
    }
}

// Data class — otomatis mendapat equals, hashCode, toString, copy
data class Produk(
    val id: Int,
    val nama: String,
    val harga: Int,
    val stok: Int = 0
)

val laptop = Produk(1, "ASUS ROG", 15000000, 10)
val laptopBaru = laptop.copy(harga = 13000000, stok = 5)
println(laptop)  // Produk(id=1, nama=ASUS ROG, harga=15000000, stok=10)

// Sealed class — untuk representasi tipe yang terbatas
sealed class Hasil<out T>
class Sukses<T>(val data: T) : Hasil<T>()
class Error(val pesan: String) : Hasil<Nothing>()
class Loading : Hasil<Nothing>()

fun handleHasil(hasil: Hasil<String>) {
    when (hasil) {
        is Sukses -> println("Data: ${hasil.data}")
        is Error -> println("Error: ${hasil.pesan}")
        is Loading -> println("Loading...")
    }
}

# 1. Download Android Studio dari https://developer.android.com/studio
#    Versi terbaru: Android Studio Ladybug (2024.2)

# 2. Instal Android Studio (wizard akan memandu)
#    - Instal Android SDK
#    - Instal Android Virtual Device (AVD)
#    - Instal SDK Build Tools

# 3. Setelah instalasi, buka SDK Manager:
#    File → Settings → Appearance → System Settings → Android SDK
#    - SDK Platforms: Android 14 (API 34) atau terbaru
#    - SDK Tools: Android SDK Build-Tools, CMake, NDK

# 4. Buat AVD (Android Virtual Device):
#    Tools → Device Manager → Create Device
#    - Pilih device (misal Pixel 8)
#    - Pilih system image (API 34)
#    - Finish

# 5. Buat proyek baru:
#    File → New → New Project
#    - Template: Empty Activity (Compose) atau Empty Views Activity
#    - Language: Kotlin
#    - Minimum SDK: API 24 (Android 7.0)
#    - Build system: Gradle (Kotlin DSL)

MyAndroidApp/
├── app/
│   ├── src/
│   │   ├── main/
│   │   │   ├── java/com/example/myapp/
│   │   │   │   ├── MainActivity.kt        ← Entry point
│   │   │   │   ├── ui/                    ← UI components
│   │   │   │   │   ├── theme/
│   │   │   │   │   └── screens/
│   │   │   │   ├── data/                  ← Data layer
│   │   │   │   │   ├── local/             ← Room database
│   │   │   │   │   └── remote/            ← API service
│   │   │   │   └── model/                 ← Data models
│   │   │   ├── res/                       ← Resources
│   │   │   │   ├── layout/               ← XML layouts (Views)
│   │   │   │   ├── values/               ← strings, colors, themes
│   │   │   │   ├── drawable/             ← Gambar, shapes
│   │   │   │   └── mipmap/              ← App icons
│   │   │   └── AndroidManifest.xml       ← Konfigurasi app
│   │   └── test/                         ← Unit tests
│   └── build.gradle.kts                  ← Konfigurasi build app
├── gradle/
├── build.gradle.kts                      ← Konfigurasi build root
├── settings.gradle.kts
└── gradle.properties

package com.example.myapp

import android.content.Intent
import android.os.Bundle
import android.util.Log
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    companion object {
        private const val TAG = "MainActivity"
    }

    // View references
    private lateinit var tvGreeting: TextView
    private lateinit var btnNavigate: Button

    // ===== LIFECYCLE METHODS =====

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)  // Set layout XML
        Log.d(TAG, "onCreate")

        // Inisialisasi views
        tvGreeting = findViewById(R.id.tvGreeting)
        btnNavigate = findViewById(R.id.btnNavigate)

        // Set teks
        tvGreeting.text = "Selamat Datang di Aplikasi Android!"

        // Navigasi ke Activity lain
        btnNavigate.setOnClickListener {
            val intent = Intent(this, DetailActivity::class.java).apply {
                putExtra("ITEM_ID", 42)
                putExtra("ITEM_NAME", "Produk Kotlin")
            }
            startActivity(intent)
        }
    }

    override fun onStart() {
        super.onStart()
        Log.d(TAG, "onStart — Activity terlihat")
    }

    override fun onResume() {
        super.onResume()
        Log.d(TAG, "onResume — Activity berinteraksi")
    }

    override fun onPause() {
        super.onPause()
        Log.d(TAG, "onPause — Activity terhalang sebagian")
    }

    override fun onStop() {
        super.onStop()
        Log.d(TAG, "onStop — Activity tidak terlihat")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.d(TAG, "onDestroy — Activity dihancurkan")
    }
}

package com.example.myapp

import android.os.Bundle
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class DetailActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_detail)

        // Menerima data dari Intent
        val itemId = intent.getIntExtra("ITEM_ID", -1)
        val itemName = intent.getStringExtra("ITEM_NAME") ?: "Unknown"

        val tvDetail: TextView = findViewById(R.id.tvDetail)
        tvDetail.text = "ID: $itemId\nNama: $itemName"

        // Enable back button di action bar
        supportActionBar?.setDisplayHomeAsUpEnabled(true)
        supportActionBar?.title = itemName
    }

    override fun onSupportNavigateUp(): Boolean {
        finish()  // Kembali ke Activity sebelumnya
        return true
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    android:padding="24dp"
    android:background="#FAFAFA">

    <TextView
        android:id="@+id/tvGreeting"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Halo, Android!"
        android:textSize="24sp"
        android:textStyle="bold"
        android:textColor="#333333"
        android:layout_marginBottom="16dp" />

    <EditText
        android:id="@+id/etInput"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Ketik sesuatu..."
        android:padding="12dp"
        android:background="@drawable/edit_text_bg"
        android:layout_marginBottom="16dp" />

    <Button
        android:id="@+id/btnNavigate"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Buka Detail"
        android:backgroundTint="#2196F3"
        android:textColor="#FFFFFF"
        android:padding="12dp" />

</LinearLayout>

package com.example.myapp.ui

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.TextView
import androidx.fragment.app.Fragment
import com.example.myapp.R

class HomeFragment : Fragment() {

    private var paramNama: String? = null

    companion object {
        fun newInstance(nama: String): HomeFragment {
            val fragment = HomeFragment()
            val args = Bundle().apply {
                putString("NAMA", nama)
            }
            fragment.arguments = args
            return fragment
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        paramNama = arguments?.getString("NAMA") ?: "Pengguna"
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_home, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        val tvWelcome: TextView = view.findViewById(R.id.tvWelcome)
        val btnToProfile: Button = view.findViewById(R.id.btnToProfile)

        tvWelcome.text = "Selamat datang, $paramNama!"

        btnToProfile.setOnClickListener {
            parentFragmentManager.beginTransaction()
                .replace(R.id.fragmentContainer, ProfileFragment())
                .addToBackStack(null)
                .commit()
        }
    }
}

package com.example.myapp

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.fragment.app.Fragment
import com.google.android.material.bottomnavigation.BottomNavigationView

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val bottomNav: BottomNavigationView = findViewById(R.id.bottomNav)

        // Load fragment awal
        if (savedInstanceState == null) {
            loadFragment(HomeFragment())
        }

        bottomNav.setOnItemSelectedListener { item ->
            val fragment: Fragment = when (item.itemId) {
                R.id.nav_home -> HomeFragment()
                R.id.nav_search -> SearchFragment()
                R.id.nav_profile -> ProfileFragment()
                else -> HomeFragment()
            }
            loadFragment(fragment)
            true
        }
    }

    private fun loadFragment(fragment: Fragment) {
        supportFragmentManager.beginTransaction()
            .replace(R.id.fragmentContainer, fragment)
            .commit()
    }
}

// Model data
data class Artikel(
    val id: Int,
    val judul: String,
    val deskripsi: String,
    val gambarUrl: String,
    val tanggal: String
)

package com.example.myapp.adapter

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.ListAdapter
import androidx.recyclerview.widget.RecyclerView
import com.example.myapp.R
import com.example.myapp.model.Artikel

class ArtikelAdapter(
    private val onItemClick: (Artikel) -> Unit
) : ListAdapter<Artikel, ArtikelAdapter.ArtikelViewHolder>(ArtikelDiffCallback()) {

    // ViewHolder — menyimpan referensi ke view
    class ArtikelViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val tvJudul: TextView = itemView.findViewById(R.id.tvJudul)
        val tvDeskripsi: TextView = itemView.findViewById(R.id.tvDeskripsi)
        val tvTanggal: TextView = itemView.findViewById(R.id.tvTanggal)
        val imgArtikel: ImageView = itemView.findViewById(R.id.imgArtikel)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ArtikelViewHolder {
        val view = LayoutInflater.from(parent.context)
            .inflate(R.layout.item_artikel, parent, false)
        return ArtikelViewHolder(view)
    }

    override fun onBindViewHolder(holder: ArtikelViewHolder, position: Int) {
        val artikel = getItem(position)

        holder.tvJudul.text = artikel.judul
        holder.tvDeskripsi.text = artikel.deskripsi
        holder.tvTanggal.text = artikel.tanggal

        // Load image dengan Glide/Coil
        // Glide.with(holder.itemView.context)
        //     .load(artikel.gambarUrl)
        //     .into(holder.imgArtikel)

        holder.itemView.setOnClickListener {
            onItemClick(artikel)
        }
    }
}

// DiffUtil — efisien membandingkan list lama vs baru
class ArtikelDiffCallback : DiffUtil.ItemCallback<Artikel>() {
    override fun areItemsTheSame(oldItem: Artikel, newItem: Artikel) =
        oldItem.id == newItem.id

    override fun areContentsTheSame(oldItem: Artikel, newItem: Artikel) =
        oldItem == newItem
}

class ArtikelListFragment : Fragment() {

    private lateinit var recyclerView: RecyclerView
    private lateinit var adapter: ArtikelAdapter

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_artikel_list, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        recyclerView = view.findViewById(R.id.rvArtikel)

        adapter = ArtikelAdapter { artikel ->
            // Handle click — navigasi ke detail
            Toast.makeText(context, "Klik: ${artikel.judul}", Toast.LENGTH_SHORT).show()
        }

        recyclerView.apply {
            layoutManager = LinearLayoutManager(context)
            adapter = this@ArtikelListFragment.adapter
            setHasFixedSize(true)
        }

        // Submit data
        val dataDummy = listOf(
            Artikel(1, "Belajar Kotlin", "Dasar-dasar Kotlin", "", "25 Jun 2026"),
            Artikel(2, "Android Studio", "Setup & konfigurasi", "", "24 Jun 2026"),
            Artikel(3, "Jetpack Compose", "UI modern Android", "", "23 Jun 2026"),
        )
        adapter.submitList(dataDummy)
    }
}

dependencies {
    // Room Database
    val roomVersion = "2.6.1"
    implementation("androidx.room:room-runtime:$roomVersion")
    implementation("androidx.room:room-ktx:$roomVersion")  // Coroutines support
    kapt("androidx.room:room-compiler:$roomVersion")        // Annotation processor

    // ViewModel & LiveData
    implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.7.0")
    implementation("androidx.lifecycle:lifecycle-livedata-ktx:2.7.0")
}

package com.example.myapp.data

import androidx.lifecycle.LiveData
import androidx.room.*

// ===== ENTITY =====
@Entity(tableName = "catatan")
data class Catatan(
    @PrimaryKey(autoGenerate = true)
    val id: Int = 0,

    @ColumnInfo(name = "judul")
    val judul: String,

    @ColumnInfo(name = "isi")
    val isi: String,

    @ColumnInfo(name = "tanggal")
    val tanggal: Long = System.currentTimeMillis(),

    @ColumnInfo(name = "favorit")
    val favorit: Boolean = false
)

// ===== DAO (Data Access Object) =====
@Dao
interface CatatanDao {

    @Query("SELECT * FROM catatan ORDER BY tanggal DESC")
    fun getAll(): LiveData<List<Catatan>>

    @Query("SELECT * FROM catatan WHERE id = :id")
    suspend fun getById(id: Int): Catatan?

    @Query("SELECT * FROM catatan WHERE judul LIKE '%' || :query || '%'")
    fun search(query: String): LiveData<List<Catatan>>

    @Query("SELECT * FROM catatan WHERE favorit = 1")
    fun getFavorites(): LiveData<List<Catatan>>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insert(catatan: Catatan)

    @Update
    suspend fun update(catatan: Catatan)

    @Delete
    suspend fun delete(catatan: Catatan)

    @Query("DELETE FROM catatan")
    suspend fun deleteAll()
}

// ===== DATABASE =====
@Database(entities = [Catatan::class], version = 1, exportSchema = false)
abstract class AppDatabase : RoomDatabase() {

    abstract fun catatanDao(): CatatanDao

    companion object {
        @Volatile
        private var INSTANCE: AppDatabase? = null

        fun getDatabase(context: Context): AppDatabase {
            return INSTANCE ?: synchronized(this) {
                val instance = Room.databaseBuilder(
                    context.applicationContext,
                    AppDatabase::class.java,
                    "app_database"
                ).build()
                INSTANCE = instance
                instance
            }
        }
    }
}

package com.example.myapp.ui

import android.app.Application
import androidx.lifecycle.*
import com.example.myapp.data.AppDatabase
import com.example.myapp.data.Catatan
import kotlinx.coroutines.launch

class CatatanViewModel(application: Application) : AndroidViewModel(application) {

    private val dao = AppDatabase.getDatabase(application).catatanDao()

    // LiveData — otomatis update UI saat data berubah
    val semuaCatatan: LiveData<List<Catatan>> = dao.getAll()
    val favoritCatatan: LiveData<List<Catatan>> = dao.getFavorites()

    private val _searchQuery = MutableLiveData<String>("")
    val searchResults: LiveData<List<Catatan>> = _searchQuery.switchMap { query ->
        if (query.isBlank()) dao.getAll()
        else dao.search(query)
    }

    fun tambah(judul: String, isi: String) {
        viewModelScope.launch {
            dao.insert(Catatan(judul = judul, isi = isi))
        }
    }

    fun hapus(catatan: Catatan) {
        viewModelScope.launch {
            dao.delete(catatan)
        }
    }

    fun toggleFavorit(catatan: Catatan) {
        viewModelScope.launch {
            dao.update(catatan.copy(favorit = !catatan.favorit))
        }
    }

    fun search(query: String) {
        _searchQuery.value = query
    }
}

package com.example.myapp.ui

import androidx.compose.foundation.layout.*
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.material3.*
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp

// ===== COMPOSABLE FUNCTION =====
@Composable
fun GreetingScreen() {
    // State — otomatis recompose saat berubah
    var nama by remember { mutableStateOf("") }
    var sapaan by remember { mutableStateOf("") }

    Column(
        modifier = Modifier
            .fillMaxSize()
            .padding(24.dp),
        horizontalAlignment = Alignment.CenterHorizontally
    ) {
        Text(
            text = "Halo, Jetpack Compose!",
            style = MaterialTheme.typography.headlineMedium,
            color = MaterialTheme.colorScheme.primary
        )

        Spacer(modifier = Modifier.height(16.dp))

        // Input field
        OutlinedTextField(
            value = nama,
            onValueChange = { nama = it },
            label = { Text("Nama Anda") },
            modifier = Modifier.fillMaxWidth()
        )

        Spacer(modifier = Modifier.height(16.dp))

        // Button
        Button(
            onClick = { sapaan = "Halo, $nama! 👋" },
            modifier = Modifier.fillMaxWidth(),
            enabled = nama.isNotBlank()
        ) {
            Text("Sapa!")
        }

        Spacer(modifier = Modifier.height(16.dp))

        // Hasil
        if (sapaan.isNotEmpty()) {
            Card(
                modifier = Modifier.fillMaxWidth(),
                colors = CardDefaults.cardColors(
                    containerColor = MaterialTheme.colorScheme.primaryContainer
                )
            ) {
                Text(
                    text = sapaan,
                    modifier = Modifier.padding(16.dp),
                    style = MaterialTheme.typography.bodyLarge
                )
            }
        }
    }
}

// Data model
data class Item(val id: Int, val nama: String, val harga: Int)

@Composable
fun ItemListScreen() {
    val items = remember {
        listOf(
            Item(1, "Laptop ASUS", 12000000),
            Item(2, "Keyboard Mekanik", 850000),
            Item(3, "Monitor 27\"", 4500000),
            Item(4, "Mouse Logitech", 350000),
        )
    }

    LazyColumn(
        modifier = Modifier.fillMaxSize(),
        contentPadding = PaddingValues(16.dp),
        verticalArrangement = Arrangement.spacedBy(8.dp)
    ) {
        items(items) { item ->
            Card(
                modifier = Modifier.fillMaxWidth()
            ) {
                Row(
                    modifier = Modifier
                        .padding(16.dp)
                        .fillMaxWidth(),
                    horizontalArrangement = Arrangement.SpaceBetween,
                    verticalAlignment = Alignment.CenterVertically
                ) {
                    Column {
                        Text(
                            text = item.nama,
                            style = MaterialTheme.typography.titleMedium
                        )
                        Text(
                            text = "Rp ${item.harga.toLocaleString()}",
                            color = MaterialTheme.colorScheme.primary,
                            style = MaterialTheme.typography.bodyMedium
                        )
                    }
                    Button(onClick = { /* Tambah ke keranjang */ }) {
                        Text("Beli")
                    }
                }
            }
        }
    }
}

// Entry point Activity
class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MaterialTheme {
                Surface(modifier = Modifier.fillMaxSize()) {
                    ItemListScreen()
                }
            }
        }
    }
}