Jetpack compose: How to convert list to flow

Introduction

This code demonstrates how to convert a static list of data into a flow in Jetpack Compose. Flows are a powerful concept in Kotlin that represent asynchronous streams of data. They are particularly useful for handling dynamic data that might change over time, such as data retrieved from a network request or a database.

Breakdown

The code is divided into two main parts:

  1. MainActivity: This class defines the main activity of the application. It sets the content of the screen using setContent and defines the layout structure using composables.
  2. MainContent: This composable function builds the UI for the main content area. It showcases converting a list to a flow and displaying the first element from the flow.

Here's a detailed breakdown of the MainContent composable:

  • colors: Defines a static list of color strings.
  • colorFlow: Converts the colors list to a flow using the asFlow extension function. This allows the data to be treated as a stream.
  • color by colorFlow.collectAsState(initial = "Red"): This line collects the first value emitted by the colorFlow and stores it in a composable state variable named color. The initial value is set to "Red" in case the flow doesn't immediately emit a value.
  • Box: This composable defines a container that fills the entire available space and centers its content.
  • Text: This composable displays the current value of the color state variable with a font size of 40sp.

Summary

This code snippet effectively demonstrates how to leverage flows in Jetpack Compose. By converting a static list to a flow, you can potentially manipulate the data stream or integrate it with asynchronous data sources in the future. The collectAsState function helps bridge the gap between flows and composable state, allowing you to display the current value of the flow in a composable UI.


MainActivity.kt 

package com.cfsuman.composestate

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.*
import androidx.compose.material.*
import androidx.compose.runtime.Composable
import androidx.compose.runtime.collectAsState
import androidx.compose.runtime.getValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.unit.sp
import com.cfsuman.composestate.ui.theme.ComposeStateTheme
import kotlinx.coroutines.flow.asFlow


class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            ComposeStateTheme {
                Scaffold(
                    topBar = { TopAppBar(
                        title = {
                            Text(text = "Compose - Convert list to flow")
                        }
                    )},
                    content = { MainContent() },
                    backgroundColor = Color(0xFFEDEAE0)
                )
            }
        }
    }
}


@Composable
fun MainContent() {
    val colors = listOf("Red","Green","Blue","Yellow","Pink")
    val colorFlow = colors.asFlow()

    val color by colorFlow
        .collectAsState(initial = "Red")

    Box(
        Modifier.fillMaxSize(),
        contentAlignment = Alignment.Center
    ) {
        Text(text = color, fontSize = 40.sp)
    }
}
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