[android] データの非同期処理（Coroutines / Flow）

MainViewModel.kt

import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.launch

class MainViewModel : ViewModel() {
    private val _counter = MutableStateFlow(0)
    val counter: StateFlow<Int> = _counter

    fun startCounting() {
        viewModelScope.launch {
            for (i in 1..10) {
                delay(1000) // 1秒待つ
                _counter.value = i
            }
        }
    }
}

package com.example.myapplicationcoroutine

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.activity.enableEdgeToEdge
import androidx.activity.viewModels
import androidx.lifecycle.lifecycleScope
import kotlinx.coroutines.flow.collectLatest
import kotlinx.coroutines.launch
import android.widget.Button
import android.widget.TextView
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.material3.Scaffold
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.tooling.preview.Preview
import com.example.myapplicationcoroutine.ui.theme.MyApplicationCoroutineTheme

class MainActivity : ComponentActivity() {

    private val viewModel: MainViewModel by viewModels()

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

        val counterTextView = findViewById<TextView>(R.id.counterTextView)
        val startButton = findViewById<Button>(R.id.startButton)

        // ボタンを押すとカウントスタート
        startButton.setOnClickListener {
            viewModel.startCounting()
        }

        // Flowを監視してUI更新
        lifecycleScope.launch {
            viewModel.counter.collectLatest { value ->
                counterTextView.text = "カウント: $value"
            }
        }
    }
}

<?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="16dp">

    <TextView
        android:id="@+id/counterTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="カウント: 0"
        android:textSize="24sp"
        android:layout_marginBottom="24dp"/>

    <Button
        android:id="@+id/startButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="カウント開始"/>
</LinearLayout>