Navigating between composables in Android Kotlin

Introduction

Navigation lets users move between different screens in your app. It helps organize your app into small parts called composables.

When you want to open a new screen after a button click.

When you want to go back to the previous screen.

When you want to switch between different app sections like Home and Settings.

When you want to pass simple data from one screen to another.

Syntax

Android Kotlin

val navController = rememberNavController()
NavHost(navController, startDestination = "screen1") {
  composable("screen1") { Screen1(navController) }
  composable("screen2") { Screen2(navController) }
}

// To navigate:
navController.navigate("screen2")

NavController controls navigation actions.

NavHost holds the navigation graph with all screens.

Examples

Navigate to the screen with route "profile".

Android Kotlin

navController.navigate("profile")

Go back to the previous screen.

Android Kotlin

navController.popBackStack()

Define a screen that accepts an argument called itemId.

Android Kotlin

composable("details/{itemId}") { backStackEntry ->
  val itemId = backStackEntry.arguments?.getString("itemId")
  DetailsScreen(itemId)
}

Navigate to the details screen passing 42 as itemId.

Android Kotlin

navController.navigate("details/42")

Sample App

This app has two screens: Home and Details. On Home, a button navigates to Details. On Details, a button goes back to Home.

Android Kotlin

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material3.*
import androidx.compose.runtime.Composable
import androidx.navigation.compose.*

class MainActivity : ComponentActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContent {
      val navController = rememberNavController()
      NavHost(navController, startDestination = "home") {
        composable("home") { HomeScreen(navController) }
        composable("details") { DetailsScreen(navController) }
      }
    }
  }
}

@Composable
fun HomeScreen(navController: NavHostController) {
  Scaffold(
    topBar = { TopAppBar(title = { Text("Home") }) },
    content = {
      Button(onClick = { navController.navigate("details") }) {
        Text("Go to Details")
      }
    }
  )
}

@Composable
fun DetailsScreen(navController: NavHostController) {
  Scaffold(
    topBar = { TopAppBar(title = { Text("Details") }) },
    content = {
      Button(onClick = { navController.popBackStack() }) {
        Text("Back to Home")
      }
    }
  )
}

Important Notes

Always use rememberNavController() inside a composable to keep navigation state.

Use clear route names to avoid confusion.

Passing data between screens requires defining route parameters and reading them from backStackEntry.

Summary

Navigation connects different composables as screens.

Use NavHost and NavController to manage navigation.

Navigate with navController.navigate(route) and go back with popBackStack().

Practice

1. What is the main purpose of NavController in Jetpack Compose navigation?

easy

A. To create UI elements inside a composable

B. To handle database operations

C. To manage navigation between composable screens

D. To style composables with themes

Solution

1. Step 1: Understand the role of NavController

   NavController is responsible for controlling navigation actions between composables in an app.

2. Step 2: Differentiate from other components

   It does not create UI elements, handle databases, or style components; those are handled by other parts of Compose or Android.

3. Final Answer:

   To manage navigation between composable screens -> Option C

4. Quick Check:

   NavController manages navigation [OK]

Hint: NavController controls screen changes in Compose [OK]

Common Mistakes:

• Confusing NavController with UI creation
• Thinking NavController handles data or styling
• Mixing NavController with ViewModel

2. Which of the following is the correct syntax to navigate to a composable with route "profile" using NavController named navController?

easy

A. navController.navigate("profile")

B. navController.goTo("profile")

C. navController.move("profile")

D. navController.open("profile")

Solution

1. Step 1: Recall the navigation method

   The correct method to navigate is navigate() on NavController.

2. Step 2: Check method names

   Only navigate() is valid; others like goTo(), move(), or open() do not exist.

3. Final Answer:

   navController.navigate("profile") -> Option A

4. Quick Check:

   Use navigate() to change screens [OK]

Hint: Use navigate() method on NavController [OK]

Common Mistakes:

• Using non-existent methods like goTo or move
• Forgetting to pass route as a string
• Calling navigation on wrong object

3. Given this code snippet inside a composable:

val navController = rememberNavController()
Button(onClick = { navController.navigate("details") }) {
  Text("Go to Details")
}

What happens when the button is clicked?

medium

A. The app navigates to the composable with route "details"

B. The app closes immediately

C. Nothing happens because navigate() is incorrect

D. The app crashes due to missing NavHost

Solution

1. Step 1: Understand the button's onClick action

   The button calls navController.navigate("details") which triggers navigation to the "details" route.

2. Step 2: Consider NavHost presence

   Assuming NavHost is set up correctly with "details" route, navigation will succeed and show that screen.

3. Final Answer:

   The app navigates to the composable with route "details" -> Option A

4. Quick Check:

   Button triggers navigate() to details [OK]

Hint: Button click calls navigate() to change screen [OK]

Common Mistakes:

• Assuming navigate() does nothing
• Confusing navigation with app closing
• Ignoring NavHost setup requirement

4. Consider this code snippet:

navController.navigate("home")
navController.popBackStack()

What is the likely problem here?

medium

A. popBackStack() is not a valid NavController method

B. Calling popBackStack() immediately after navigate() may prevent navigation

C. navigate() requires a NavHost to be null

D. No problem; this code navigates then goes back correctly

Solution

1. Step 1: Analyze the sequence of calls

   Calling navigate("home") pushes a new screen, but immediately calling popBackStack() removes the top screen.

2. Step 2: Understand effect on navigation

   This means the navigation to "home" is undone immediately, so user may not see the new screen.

3. Final Answer:

   Calling popBackStack() immediately after navigate() may prevent navigation -> Option B

4. Quick Check:

   popBackStack() right after navigate() cancels navigation [OK]

Hint: Don't popBackStack() right after navigate() [OK]

Common Mistakes:

• Thinking popBackStack() is invalid
• Assuming navigation always succeeds despite popBackStack()
• Ignoring call order effects

5. You want to navigate from a composable "list" to "details/{itemId}" passing an item ID as argument. Which code correctly navigates to details screen with itemId = 42?

hard

A. navController.navigate("details/{itemId}")

B. navController.navigate("details")

C. navController.navigate("details?itemId=42")

D. navController.navigate("details/42")

Solution

1. Step 1: Understand route parameter usage

   When route has a placeholder like "details/{itemId}", you replace {itemId} with actual value in the route string.

2. Step 2: Check each option

   navController.navigate("details/42") correctly replaces {itemId} with 42. navController.navigate("details") misses the parameter. navController.navigate("details?itemId=42") uses query syntax which is not standard here. navController.navigate("details/{itemId}") uses the placeholder literally, which won't work.

3. Final Answer:

   navController.navigate("details/42") -> Option D

4. Quick Check:

   Replace {itemId} with actual value in route [OK]

Hint: Replace placeholders with actual values in route string [OK]

Common Mistakes:

• Passing route with placeholder instead of value
• Using query parameters incorrectly
• Omitting required route arguments