jetpack compose - animateFloatAsState

MainActivity.kt

package com.cfsuman.jetpackcompose

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.activity.compose.setContent
import androidx.compose.animation.core.FastOutSlowInEasing
import androidx.compose.animation.core.animateFloatAsState
import androidx.compose.animation.core.tween
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.*
import androidx.compose.material.*
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.Favorite
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.alpha
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContent {
            MainContent()
        }
    }


    @Composable
    fun MainContent(){
        val isOpaque = remember { mutableStateOf(value = true) }

        val alpha: Float by animateFloatAsState(
            targetValue = if (isOpaque.value) 1f else 0.2f,
            animationSpec = tween(
                durationMillis = 3000, // animation duration
                easing = FastOutSlowInEasing // animation easing
            )
        )

        Column(
            modifier = Modifier
                .fillMaxSize()
                .background(Color(0xFFFFF8DC))
                .padding(16.dp),
            verticalArrangement = Arrangement.spacedBy(16.dp),
            horizontalAlignment = Alignment.CenterHorizontally
        ) {
            Button(
                onClick = { isOpaque.value = !isOpaque.value },
                colors = ButtonDefaults.buttonColors(
                    Color(0xFF9E1B32), Color(0xCCFFFFFF)
                )
            ) {
                Text(text = "Animate Opacity")
            }

            Icon(
                Icons.Filled.Favorite,
                "Localized description",
                tint = Color(0xFFE30022),
                modifier = Modifier
                    .size(300.dp)
                    .alpha(alpha = alpha)
            )
        }
    }


    @Preview
    @Composable
    fun ComposablePreview(){
        //MainContent()
    }
}