Unable to initialize the button in fragment in kotlin

Question

I am doing a basic android project to implement the fragments inside a single activity using Navigation Controller and Navigation Host. Inside a fragment I have two buttons and I have already initialize those two buttons with the id's inside the onCreateView() method. But whenever I was going to run the application in avd, the application is getting crashed. Please help me to solve this issue. Down below, I am posting all the details regarding to this problem:

MainFragment.kt

class MainFragment : Fragment() {

    lateinit var view_balances_button : Button;
    lateinit var pay_someone_button : Button;
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        val view: View = inflater!!.inflate(R.layout.fragment_main, container, false)

        view_balances_button.findViewById<Button>(R.id.view_balances_button)
        pay_someone_button.findViewById<Button>(R.id.pay_someone_button)

        view_balances_button.setOnClickListener {
            findNavController().navigate(R.id.action_mainFragment_to_viewBalanceFragment2)
        }

        pay_someone_button.setOnClickListener {
            findNavController().navigate(R.id.action_mainFragment_to_viewPeopleFragment2)
        }

        // Inflate the layout for this fragment

        return view
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)



    }


}

fragment_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="@dimen/android_default_padding"
    tools:context=".MainFragment">

    <!-- TODO: Update blank fragment layout -->

    <Button
        android:id="@+id/view_balances_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="@string/button_view_balances" />

    <Button
        android:id="@+id/pay_someone_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="@dimen/android_default_padding"
        android:text="@string/button_pay_someone" />

</LinearLayout>

MainActivity.kt

package com.shankhadeep.navigationcomponentjetpack

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.navigation.findNavController
import androidx.navigation.ui.NavigationUI

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

        NavigationUI.setupActionBarWithNavController(this,findNavController(R.id.nav_host_fragment))
    }
}

activty_main.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/my_navigation"/>

</FrameLayout>

Error message image

Error shown in the logcat

score 0 · Accepted Answer · answered May 26 '21 at 17:41

in fragment onCreateView View view assigned to view so u need to call view.findViewById(R.id.yourID)

changes

findNavController().navigate(R.id.action_mainFragment_to_viewBalanceFragment2)

to

val navController = Navigation.findNavController(requireActivity(), R.id.nav_host_fragment)

then use navigate

navController.navigate(R.id.yourNavigation)

modified code

override fun onCreateView(
                inflater: LayoutInflater, container: ViewGroup?,
                savedInstanceState: Bundle?
            ): View? {
        
                val view: View = inflater!!.inflate(R.layout.fragment_main, container, false)
        
                val navController = Navigation.findNavController(requireActivity(), R.id.nav_host_fragment)

                view_balances_button = view.findViewById(R.id.view_balances_button)
                pay_someone_button = view.findViewById(R.id.pay_someone_button)
        
                view_balances_button!!.setOnClickListener {
                    navController.navigate(R.id.action_mainFragment_to_viewBalanceFragment2)
                }
        
                pay_someone_button!!.setOnClickListener {
                    navController.navigate(R.id.action_mainFragment_to_viewPeopleFragment2)
                }
        
                // Inflate the layout for this fragment
        
                return view
            }

score 0 · Answer 2 · answered May 26 '21 at 18:00

We face some crashes initializing view in onCreateView.

You should inflate your layout in onCreateView but shouldn't initialize other views using findViewById in onCreateView.

Because sometimes view is not properly initialized. So always use findViewById in onViewCreated(when view is fully created) and it also passes the view as parameter.

onViewCreated is a make sure that view is fully created.

onViewCreated android Documentation

Called immediately after onCreateView(android.view.LayoutInflater, android.view.ViewGroup, android.os.Bundle) has returned, but before any saved state has been restored in to the view. This gives subclasses a chance to initialize themselves once they know their view hierarchy has been completely created. The fragment's view hierarchy is not however attached to its parent at this point.

Refer to this stack overflow question
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Unable to initialize the button in fragment in kotlin

2 Answers2