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androidkotlinandroid-tablayout

Why am I not able to start my activity while using TabLayout in android?

I have 3 fragments Easy , Medium and Hard, the defualt one is Easy, so, I am using Navigation graph to navigate to respective fragments when clicked on the Tabs, for example if I click on Medium Tab, I should navigate to Medium Fragment. So, now when I run the code, it's showing following error enter image description here

Below is my code. activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
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">

    <!-- android:numColumns=2 is the number of columns for Grid View
           android:horizontalSpacing is the space between horizontal
grid items -->
    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toTopOf="parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph" />

</androidx.constraintlayout.widget.ConstraintLayout>

Below is the code of my MainActivity.kt

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.navigation.NavController
import androidx.navigation.Navigation

class MainActivity : AppCompatActivity() {

    private lateinit var navController: NavController

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

        // Initialize the NavController
        navController = Navigation.findNavController(this,
R.id.nav_host_fragment)
    }

    // Ensure that the back button works with the NavController
    override fun onSupportNavigateUp(): Boolean {
        return navController.navigateUp() || super.onSupportNavigateUp()
    }
}

Below is the code of my EasyFragment, code is same for other 2 fragments also

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.navigation.fragment.findNavController
import androidx.viewpager2.widget.ViewPager2
import com.google.android.material.tabs.TabLayout
import com.google.android.material.tabs.TabLayoutMediator

class EasyFragment : Fragment() {

    private lateinit var viewPager: ViewPager2
    private lateinit var tabLayout: TabLayout

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_easy, container, false)

        // Initialize the ViewPager2 and TabLayout
        viewPager = view.findViewById(R.id.viewPager)
        tabLayout = view.findViewById(R.id.tabLayout)

        // Create an array of fragment instances for each tab
        val fragments = listOf(
            EasyFragment(), // You should create separate fragment
classes for Easy, Medium, and Hard tabs
            MediumFragment(),
            HardFragment()
        )

        val adapter = ViewPagerAdapter(requireActivity(), fragments)
        viewPager.adapter = adapter


        return view
    }
}

Below is the Adapter class code

import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import androidx.viewpager2.adapter.FragmentStateAdapter

class ViewPagerAdapter(
    fragmentActivity: FragmentActivity,
   private val fragments: List<Fragment>
):FragmentStateAdapter(fragmentActivity) {
    override fun getItemCount(): Int {
        return fragments.size
    }

    override fun createFragment(position: Int): Fragment {
        when (position) {
            0-> return EasyFragment()
            1-> return MediumFragment()
            2-> return HardFragment()
        }
        return EasyFragment()
    }

Below is the Navigation Graph code nav_graph.xml

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/nav_graph"
    app:startDestination="@id/easyFragment">

    <fragment
        android:id="@+id/easyFragment"
        android:name="com.example.tablayoutdemo.EasyFragment"
        android:label="fragment_easy"
        tools:layout="@layout/fragment_easy" >
        <action
            android:id="@+id/action_easyFragment_to_mediumFragment"
            app:destination="@id/mediumFragment" />
        <action
            android:id="@+id/action_easyFragment_to_hardFragment"
            app:destination="@id/hardFragment" />
        <action
            android:id="@+id/action_easyFragment_to_easyFragment"
            app:destination="@+id/easyFragment"/>
    </fragment>
    <fragment
        android:id="@+id/mediumFragment"
        android:name="com.example.tablayoutdemo.MediumFragment"
        android:label="fragment_medium"
        tools:layout="@layout/fragment_medium" />
    <fragment
        android:id="@+id/hardFragment"
        android:name="com.example.tablayoutdemo.HardFragment"
        android:label="fragment_hard"
        tools:layout="@layout/fragment_hard" />
</navigation>
Solution

  • It says on your error code that activity does not have a nav controller set.

    this caused because of improper initialization.

    try this instead, Use NavHostFragment.

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