Tugas Pertemuan 12 Pemrograman Perangkat Bergerak B

Nama    : Fadaukas Daffa Tajuddin

NRP      : 5025231149

Kelas    : PPB (B)

Membuat Login Sederhana

Aplikasi ini dirancang untuk mendemonstrasikan alur autentikasi sederhana (Login & Registrasi) dengan penyimpanan lokal. Menggunakan pola arsitektur MVVM untuk memisahkan logika bisnis dari antarmuka pengguna, serta Room Database sebagai Single Source of Truth untuk data pengguna.

Data Layer (Model & Room)

AppDatabase

package com.example.login.data

import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase

@Database(entities = [User::class], version = 1, exportSchema = false)
abstract class AppDatabase : RoomDatabase() {
    abstract fun userDao(): UserDao

    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
            }
        }
    }
}

User

package com.example.login.data

import androidx.room.Entity
import androidx.room.PrimaryKey

@Entity(tableName = "users")
data class User(
    @PrimaryKey(autoGenerate = true) val id: Int = 0,
    val username: String,
    val password: String
)

UserDao

package com.example.login.data

import androidx.room.Dao
import androidx.room.Insert
import androidx.room.OnConflictStrategy
import androidx.room.Query

@Dao
interface UserDao {
    @Query("SELECT * FROM users WHERE username = :username AND password = :password LIMIT 1")
    suspend fun login(username: String, password: String): User?

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun register(user: User)
}

UserRepository

package com.example.login.data

class UserRepository(private val userDao: UserDao) {
    suspend fun login(username: String, password: String): User? {
        return userDao.login(username, password)
    }

    suspend fun register(user: User) {
        userDao.register(user)
    }
}

Logic Layer

LoginViewModel

package com.example.login.ui

import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.viewModelScope
import com.example.login.data.User
import com.example.login.data.UserRepository
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.launch

class LoginViewModel(private val repository: UserRepository) : ViewModel() {

    private val _loginStatus = MutableStateFlow<String?>(null)
    val loginStatus: StateFlow<String?> = _loginStatus

    fun login(username: String, password: String) {
        if (username.isBlank() || password.isBlank()) {
            _loginStatus.value = "Username dan password tidak boleh kosong"
            return
        }
        
        viewModelScope.launch {
            val user = repository.login(username, password)
            if (user != null) {
                _loginStatus.value = "Login Berhasil! Selamat datang, ${user.username}"
            } else {
                _loginStatus.value = "Login Gagal! Username atau password salah"
            }
        }
    }

    fun register(username: String, password: String) {
        if (username.isBlank() || password.isBlank()) {
            _loginStatus.value = "Username dan password tidak boleh kosong"
            return
        }

        viewModelScope.launch {
            repository.register(User(username = username, password = password))
            _loginStatus.value = "Registrasi Berhasil! Silakan Login"
        }
    }

    fun resetStatus() {
        _loginStatus.value = null
    }
}

class LoginViewModelFactory(private val repository: UserRepository) : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(LoginViewModel::class.java)) {
            @Suppress("UNCHECKED_CAST")
            return LoginViewModel(repository) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}

UI Layer

LoginScreen

package com.example.login.ui

import androidx.compose.foundation.layout.*
import androidx.compose.material3.*
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.text.input.PasswordVisualTransformation
import androidx.compose.ui.unit.dp

@Composable
fun LoginScreen(viewModel: LoginViewModel, modifier: Modifier = Modifier) {
    var username by remember { mutableStateOf("") }
    var password by remember { mutableStateOf("") }
    val loginStatus by viewModel.loginStatus.collectAsState()
    
    val isInputValid = username.isNotBlank() && password.isNotBlank()

    Column(
        modifier = modifier
            .fillMaxSize()
            .padding(16.dp),
        horizontalAlignment = Alignment.CenterHorizontally,
        verticalArrangement = Arrangement.Center
    ) {
        Text(text = "Login", style = MaterialTheme.typography.headlineMedium)
        
        Spacer(modifier = Modifier.height(32.dp))

        OutlinedTextField(
            value = username,
            onValueChange = { 
                username = it
                viewModel.resetStatus()
            },
            label = { Text("Username") },
            modifier = Modifier.fillMaxWidth(),
            isError = username.isEmpty() && loginStatus != null && loginStatus!!.contains("kosong"),
            singleLine = true
        )

        Spacer(modifier = Modifier.height(8.dp))

        OutlinedTextField(
            value = password,
            onValueChange = { 
                password = it
                viewModel.resetStatus()
            },
            label = { Text("Password") },
            visualTransformation = PasswordVisualTransformation(),
            modifier = Modifier.fillMaxWidth(),
            isError = password.isEmpty() && loginStatus != null && loginStatus!!.contains("kosong"),
            singleLine = true
        )

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

        Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.SpaceEvenly) {
            Button(
                onClick = { viewModel.login(username, password) },
                enabled = isInputValid
            ) {
                Text("Login")
            }
            Button(
                onClick = { viewModel.register(username, password) },
                enabled = isInputValid
            ) {
                Text("Register")
            }
        }

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

        loginStatus?.let { status ->
            Text(
                text = status, 
                color = if (status.contains("Berhasil")) MaterialTheme.colorScheme.primary else MaterialTheme.colorScheme.error
            )
        }
    }
}

Fitur Utama

• Validasi Ketat: Sistem mencegah pengiriman data kosong (null/blank) baik melalui UI (tombol terkunci) maupun logika di ViewModel.
• Room Persistence: Data pengguna tersimpan secara permanen di database lokal smartphone.
• Feedback Reaktif: Menggunakan StateFlow untuk menampilkan pesan sukses/gagal secara instan tanpa perlu memuat ulang halaman.
• Injeksi ViewModel: Menggunakan ViewModelProvider.Factory untuk mengirimkan instance repository ke ViewModel di MainActivity.