StateFlow for observable state in Kotlin - Mini Project: Build & Apply

StateFlow for observable state

📖 Scenario: You are building a simple Kotlin program that tracks the temperature in a room. You want to use StateFlow to hold the temperature value so that other parts of the program can observe changes to it.

🎯 Goal: Create a StateFlow to hold the temperature value, update it, and observe the changes by printing the new temperature whenever it updates.

📋 What You'll Learn

Create a MutableStateFlow with an initial temperature value

Create a read-only StateFlow from the mutable one

Update the temperature value in the MutableStateFlow

Collect the StateFlow to print temperature updates

💡 Why This Matters

🌍 Real World

StateFlow is used in Kotlin applications to hold and observe data that changes over time, such as UI state, sensor readings, or user input.

💼 Career

Understanding StateFlow is important for Kotlin developers, especially in Android development, to build reactive and responsive apps that update automatically when data changes.

1

Create a MutableStateFlow for temperature

Create a MutableStateFlow variable called _temperature with an initial value of 20 representing degrees Celsius.

Kotlin

# Create a MutableStateFlow called _temperature with initial value 20
// Your code here

Need a hint?

Use MutableStateFlow(20) to create the flow with initial value 20.

2

Create a read-only StateFlow

Create a read-only StateFlow variable called temperature that exposes the value of _temperature.

Kotlin

import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow

val _temperature = MutableStateFlow(20)
// Create a read-only StateFlow called temperature from _temperature
// Your code here

Need a hint?

Use val temperature: StateFlow = _temperature to expose the read-only flow.

3

Update the temperature value

Update the value of _temperature to 25 to simulate a temperature change.

Kotlin

import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow

val _temperature = MutableStateFlow(20)
val temperature: StateFlow = _temperature

// Update _temperature value to 25
// Your code here

Need a hint?

Use _temperature.value = 25 to update the temperature.

4

Collect and print temperature updates

Write a main function that collects the temperature StateFlow and prints the updated temperature values. Use runBlocking to run the coroutine and collect only the first two values.

Kotlin

import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.flow.collect

val _temperature = MutableStateFlow(20)
val temperature: StateFlow = _temperature

_temperature.value = 25

// Write main function to collect temperature and print updates
// Your code here

Need a hint?

Use runBlocking and temperature.collect to print updates. Use take(2) to collect only the first two values.