Android Basics: Navigation backstack

[lbrunsvold]

URL of codelab

https://developer.android.com/codelabs/basic-android-kotlin-training-navigation-backstack?continue=https%3A%2F%2Fdeveloper.android.com%2Fcourses%2Fpathways%2Fandroid-basics-kotlin-unit-3-pathway-4%23codelab-https%3A%2F%2Fdeveloper.android.com%2Fcodelabs%2Fbasic-android-kotlin-training-navigation-backstack#2 In which task and step of the codelab can this issue be found?

3. Implement Up button behavior

Describe the problem Click the back/up button the application quits/exits stops.

Steps to reproduce?

1. Go to... any fragment other than the start fragment
2. Click on... the back arrow or up arrow in the action bar.
3. See error... kotlin.UninitializedPropertyAccessException: lateinit property navController has not been initialized at com.example.cupcake.MainActivity.onSupportNavigateUp(MainActivity.kt:52) Versions Android Studio version: 2020.3.1 Patch 2 API version of the emulator: 30.9.5-7820599

Additional information Include screenshots if they would be useful in clarifying the problem. package com.example.cupcake

import android.os.Bundle import androidx.appcompat.app.AppCompatActivity import androidx.navigation.NavController import androidx.navigation.fragment.NavHostFragment import androidx.navigation.ui.setupActionBarWithNavController

/**

• Activity for cupcake order flow. */ class MainActivity : AppCompatActivity(R.layout.activity_main) {

  // Make navController a class variable so you can use it in another method.

  private lateinit var navController: NavController

  // override the onCreate() method to set up the navigation controller. Get an instance of // NavController from the NavHostFragment. // Make a call to setupActionBarWithNavController(navController) passing in the instance of // NavController. This will do the following: Show a title in the app bar based off of the // destination's label, and display the Up button whenever you're not on a top-level // destination.

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

  val navHostFragment = supportFragmentManager
      .findFragmentById(R.id.nav_host_fragment) as NavHostFragment
  val navController = navHostFragment.navController
  
  setupActionBarWithNavController(navController)

  }

  override fun onSupportNavigateUp(): Boolean { return navController.navigateUp() || super.onSupportNavigateUp() }

}

[lbrunsvold]

removed val in front of navController in onCreate. The app runs fine.