【Kotlinプログラム入門】 Jetpack Composeで変数の値を判定して文字の色を変えるサンプルプログラムです！

package com.example.sample1

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Surface
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.text.TextStyle
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.sp
import com.example.sample1.ui.theme.Sample1Theme

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            Sample1Theme {
                Surface(
                    modifier = Modifier.fillMaxSize(),
                    color = MaterialTheme.colorScheme.background
                ) {
                    TextColorChanger()
                }
            }
        }
    }
}

@Composable
fun TextColorChanger() {
    // 文字の色を判定するために使用する変数
    var textValue by remember { mutableStateOf("Value1") }

    // 条件によって色を決定
    val textColor = when (textValue) {
        "Value1" -> Color.Red    //赤
        "Value2" -> Color.Blue   //青
        else -> Color.Black      //黒
    }

    // UIを構築
    Column(
        modifier = Modifier
            .fillMaxSize()
            .background(Color.White),
        verticalArrangement = Arrangement.Center
    ) {
        Text(
            text = "Sample Text",
            color = textColor, // テキストの色を設定
            style = TextStyle(fontSize = 24.sp)
        )
    }
}

@Preview
@Composable
fun PreviewTextColorChanger() {
    TextColorChanger()
}