Error message when testing an app in the Android Studio emulator: 'The app keeps stopping'

Question

When I try an app I was developing in the Android Studio emulator, the following message appears: 'App keeps stopping' and it doesn't open.

This is the code for the MainActivity:

import android.content.Intent
import android.os.Bundle
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.findNavController
import androidx.navigation.ui.AppBarConfiguration
import androidx.navigation.ui.setupActionBarWithNavController
import com.example.bookapplication.databinding.ActivityMainBinding

  class MainActivity : AppCompatActivity() {

    private lateinit var appBarConfiguration: AppBarConfiguration
    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        binding = ActivityMainBinding.inflate(layoutInflater)
       setContentView(binding.root)

        val navController = findNavController(R.id.nav_host_fragment_content_main)
        appBarConfiguration = AppBarConfiguration(navController.graph)
        setupActionBarWithNavController(navController, appBarConfiguration)

        binding.libroLeidos.setOnClickListener { Toast.makeText(this, "Entrando en Libros Leídos", Toast.LENGTH_LONG).show()
            val primerIntent = Intent(this, librosLeidos::class.java)
            startActivity(primerIntent)
        }
        binding.libroPendiente.setOnClickListener { Toast.makeText(this, "Entrando en Libros Pendientes", Toast.LENGTH_LONG).show()
            val segundoIntent = Intent(this, librosPendientes::class.java)
            startActivity(segundoIntent)
        }
    }} 

On the other hand, in the LogCat, I get this message:

Process: com.example.bookapplication, PID: 14919
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bookapplication/com.example.bookapplication.MainActivity}: java.lang.IllegalArgumentException: ID does not reference a View inside this Activity
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.IllegalArgumentException: ID does not reference a View inside this Activity
        at android.app.Activity.requireViewById(Activity.java:3231)
        at androidx.core.app.ActivityCompat.requireViewById(ActivityCompat.java:368)
        at androidx.navigation.Navigation.findNavController(Navigation.java:58)
        at androidx.navigation.ActivityKt.findNavController(Activity.kt:30)
        at com.example.bookapplication.MainActivity.onCreate(MainActivity.kt:24)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 

The problem is that I don't know where to go to fix it. I am new to this and there are many things that are beyond me. I have found other similar questions but I have not understood well how to proceed.

Thank you very much.

Answer 1

The stacktrace from logcat points you to the call to findNavController (which appears to be on line 24 in your source code), where it says that it can't find the id R.id.nav_host_fragment_content_main in your view.

Is R.id.nav_host_fragment_content_main defined in activity_main.xml? If so, the second call to setContentView() is replacing that view with whatever is in binding.root. In that case, removing the second call could fix your issue.

If R.id.nav_host_fragment_content_main is supposed to be defined in binding.root, I think you'll need to include the implementation of com.example.bookapplication.databinding.ActivityMainBinding in your question so we can better understand what' going on.

In any case, you shouldn't call setContentView() twice, as @TylerV said.