package com.example.repositorypattern
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.viewModels
import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.viewModelScope
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import android.widget.Button
import android.widget.TextView
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.collectLatest
import kotlinx.coroutines.launch
// Data class representing a User
data class User(val id: Int, val name: String)
// Repository interface
interface UserRepository {
suspend fun getUsers(): List<User>
}
// Implementation of UserRepository with fake data
class UserRepositoryImpl : UserRepository {
override suspend fun getUsers(): List<User> {
// Simulate network or database delay
kotlinx.coroutines.delay(500)
return listOf(
User(1, "Alice"),
User(2, "Bob"),
User(3, "Charlie")
)
}
}
// ViewModel using the repository
class UserViewModel(private val repository: UserRepository) : ViewModel() {
private val _users = MutableStateFlow<List<User>>(emptyList())
val users: StateFlow<List<User>> = _users
fun loadUsers() {
viewModelScope.launch {
val result = repository.getUsers()
_users.value = result
}
}
}
// Factory to create UserViewModel with repository
class UserViewModelFactory(private val repository: UserRepository) : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
if (modelClass.isAssignableFrom(UserViewModel::class.java)) {
@Suppress("UNCHECKED_CAST")
return UserViewModel(repository) as T
}
throw IllegalArgumentException("Unknown ViewModel class")
}
}
// Simple RecyclerView Adapter for User list
class UserAdapter(private var users: List<User>) : RecyclerView.Adapter<UserAdapter.UserViewHolder>() {
class UserViewHolder(val textView: TextView) : RecyclerView.ViewHolder(textView)
override fun onCreateViewHolder(parent: android.view.ViewGroup, viewType: Int): UserViewHolder {
val textView = TextView(parent.context).apply {
textSize = 20f
setPadding(16, 16, 16, 16)
}
return UserViewHolder(textView)
}
override fun onBindViewHolder(holder: UserViewHolder, position: Int) {
holder.textView.text = users[position].name
}
override fun getItemCount() = users.size
fun updateUsers(newUsers: List<User>) {
users = newUsers
notifyDataSetChanged()
}
}
// Activity displaying the user list
class UserListActivity : ComponentActivity() {
private val repository = UserRepositoryImpl()
private val viewModel: UserViewModel by viewModels { UserViewModelFactory(repository) }
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// Root layout
val rootLayout = android.widget.LinearLayout(this).apply {
orientation = android.widget.LinearLayout.VERTICAL
setPadding(16, 16, 16, 16)
}
// RecyclerView for users
val recyclerView = RecyclerView(this).apply {
layoutManager = LinearLayoutManager(this@UserListActivity)
}
val adapter = UserAdapter(emptyList())
recyclerView.adapter = adapter
// Refresh button
val refreshButton = Button(this).apply {
text = "Refresh"
setOnClickListener {
viewModel.loadUsers()
}
}
rootLayout.addView(recyclerView, android.widget.LinearLayout.LayoutParams.MATCH_PARENT, 0, 1f)
rootLayout.addView(refreshButton, android.widget.LinearLayout.LayoutParams.MATCH_PARENT, android.widget.LinearLayout.LayoutParams.WRAP_CONTENT)
setContentView(rootLayout)
// Observe users from ViewModel
viewModel.users
.collectLatest { users ->
adapter.updateUsers(users)
}
// Load users initially
viewModel.loadUsers()
}
}This solution shows the repository pattern by defining a UserRepository interface that abstracts data fetching. The UserRepositoryImpl class simulates fetching users from a data source.
The UserViewModel uses this repository to load users asynchronously and exposes a StateFlow to the UI.
The UserListActivity sets up a simple UI with a RecyclerView to display users and a Refresh button to reload data. It observes the ViewModel's user list and updates the UI accordingly.
This pattern helps separate data logic from UI, making the app easier to maintain and test.
