RecyclerView (with Adapter) doesnt show my items - kotlin

Question

I am using RecyclerView to show my items. But when i save an item, recyclerView doesnt show it. I am saving my items with a custom dialog. So the saving happens in the same fragment with my recycler view's fragment. When i save item, first i dont get any error but recyclerView doesnt show any items. But when i navigate to another fragment and navigate back, recyclerView doesnt show anything again and this time i am getting this error;
java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.cardview.widget.CardView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.ahmetkaan.kediy.Adapter.CategoriesAdapter.onBindViewHolder(CategoriesAdapter.kt:56)
at com.ahmetkaan.kediy.Adapter.CategoriesAdapter.onBindViewHolder(CategoriesAdapter.kt:12)
at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7065)
at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7107)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012)
at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6279)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
at androidx.recyclerview.widget.LayoutState.next(LayoutState.java:98)
at androidx.recyclerview.widget.StaggeredGridLayoutManager.fill(StaggeredGridLayoutManager.java:1607)
at androidx.recyclerview.widget.StaggeredGridLayoutManager.onLayoutChildren(StaggeredGridLayoutManager.java:683)
at androidx.recyclerview.widget.StaggeredGridLayoutManager.onLayoutChildren(StaggeredGridLayoutManager.java:605)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
at androidx.recyclerview.widget.RecyclerView.onMeasure(RecyclerView.java:3540)
at android.view.View.measure(View.java:25202)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6937)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1204)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:723)
at android.view.View.measure(View.java:25202)
at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:811)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.measure(BasicMeasure.java:466)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.measureChildren(BasicMeasure.java:134)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:278)
at androidx.constraintlayout.core.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:120)
at androidx.constraintlayout.widget.ConstraintLayout.resolveSystem(ConstraintLayout.java:1594)
at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1708)
at android.view.View.measure(View.java:25202)
at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1414)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.widget.ScrollView.onMeasure(ScrollView.java:452)
at android.view.View.measure(View.java:25202)
at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:811)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.measure(BasicMeasure.java:466)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.measureChildren(BasicMeasure.java:134)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:278)
at androidx.constraintlayout.core.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:120)
at androidx.constraintlayout.widget.ConstraintLayout.resolveSystem(ConstraintLayout.java:1594)
at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1708)
at android.view.View.measure(View.java:25202)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6937)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:25202)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6937)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:25202)
at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:811)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.measure(BasicMeasure.java:466)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.measureChildren(BasicMeasure.java:134)
at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:278)
at androidx.constraintlayout.core.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:120)
at androidx.constraintlayout.widget.ConstraintLayout.resolveSystem(ConstraintLayout.java:1594)
at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1708)
at android.view.View.measure(View.java:25202)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6937)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:145)
at android.view.View.measure(View.java:25202)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6937)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
at android.view.View.measure(View.java:25202)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6937)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:25202)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6937)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
at android.view.View.measure(View.java:25202)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6937)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:773)
at android.view.View.measure(View.java:25202)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:3191)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1952)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2246)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1840)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7948)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1031)
at android.view.Choreographer.doCallbacks(Choreographer.java:854)
at android.view.Choreographer.doFrame(Choreographer.java:789)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1016)
at android.os.Handler.handleCallback(Handler.java:914)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:225)
at android.app.ActivityThread.main(ActivityThread.java:7564)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
My Adapter;
package com.ahmetkaan.kediy.Adapter
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.cardview.widget.CardView
import androidx.recyclerview.widget.RecyclerView
import com.ahmetkaan.kediy.R
import com.ahmetkaan.kediy.data.Categories
class CategoriesAdapter :
RecyclerView.Adapter<CategoriesAdapter.CategoriesViewHolder>() {
var listener:OnItemClickListener? = null
var arrList = ArrayList<Categories>()
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CategoriesViewHolder {
return CategoriesViewHolder(
LayoutInflater.from(parent.context).inflate(R.layout.item_kategoriler,parent,false)
)
}
override fun getItemCount(): Int {
return arrList.size
}
fun setData(arrCategoriesList: List<Categories>){
arrList = arrCategoriesList as ArrayList<Categories>
}
fun setOnClickListener(listener1: OnItemClickListener){
listener = listener1
}
override fun onBindViewHolder(holder: CategoriesViewHolder, position: Int) {
holder.itemView.findViewById<TextView>(R.id.titleCategories).text = arrList[position].title
var theme = arrList[position].theme
if (theme == 1) {
} else if (theme == 2) {
} else if (theme == 3) {
} else if (theme == 4) {
} else if (theme == 5) {
} else if (theme == 6) {
} else {
}
holder.itemView.findViewById<CardView>(R.id.cardView).setOnClickListener {
listener!!.onClicked(arrList[position].id!!)
}
}
class CategoriesViewHolder(view: View) : RecyclerView.ViewHolder(view){
}
interface OnItemClickListener{
fun onClicked(categoriesId:Int)
}
}
My Main Fragment;
package com.ahmetkaan.kediy
import android.app.Dialog
import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.EditText
import android.widget.ImageView
import android.widget.Toast
import androidx.navigation.fragment.findNavController
import androidx.recyclerview.widget.StaggeredGridLayoutManager
import com.ahmetkaan.kediy.Adapter.CategoriesAdapter
import com.ahmetkaan.kediy.Adapter.NotesAdapter
import com.ahmetkaan.kediy.data.Categories
import com.ahmetkaan.kediy.data.CategoriesDatabase
import com.ahmetkaan.kediy.databinding.FragmentKategorilerBinding
import kotlinx.coroutines.launch
class Kategoriler : BaseFragment() {
private lateinit var binding : FragmentKategorilerBinding
var arrCategories = ArrayList<Categories>()
var categoriesAdapter: CategoriesAdapter = CategoriesAdapter()
var themeChoose : Int = 0
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
binding = FragmentKategorilerBinding.inflate(inflater, container, false)
binding.geri.setOnClickListener {
var fragment = NotOlustur()
var bundle = Bundle()
bundle.putInt("categoriesId",-1)
fragment.arguments = bundle
findNavController().navigate(R.id.action_kategoriler_to_notlar, bundle)
}
binding.kategoriOlustur.setOnClickListener {
val dialog = Dialog(requireContext())
dialog.setCancelable(true)
dialog.setContentView(R.layout.kategori_olustur_dialog)
dialog.findViewById<Button>(R.id.kaydet).setOnClickListener {
if (dialog.findViewById<EditText>(R.id.enterName).text.isNullOrEmpty()) {
Toast.makeText(context,"İsim boş olamaz.", Toast.LENGTH_SHORT).show()
} else {
launch {
var categories = Categories()
categories.theme = themeChoose
categories.title = dialog.findViewById<EditText>(R.id.enterName).text.toString()
context?.let {
CategoriesDatabase.getDatabase(it).categoriesDao().insertCategories(categories)
dialog.findViewById<EditText>(R.id.enterName).setText("")
themeChoose = 0
dialog.dismiss()
}
}
}
}
dialog.findViewById<ImageView>(R.id.noneSelected).setOnClickListener {
themeChoose = 0
}
dialog.findViewById<ImageView>(R.id.theme1).setOnClickListener {
themeChoose = 1
}
dialog.findViewById<ImageView>(R.id.theme2).setOnClickListener {
themeChoose = 2
}
dialog.findViewById<ImageView>(R.id.theme3).setOnClickListener {
themeChoose = 3
}
dialog.findViewById<ImageView>(R.id.theme4).setOnClickListener {
themeChoose = 4
}
dialog.findViewById<ImageView>(R.id.theme5).setOnClickListener {
themeChoose = 5
}
dialog.findViewById<ImageView>(R.id.theme6).setOnClickListener {
themeChoose = 6
}
dialog.show()
}
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding.recyclerView.setHasFixedSize(true)
binding.recyclerView.layoutManager = StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)
launch {
context?.let {
var categories = CategoriesDatabase.getDatabase(it).categoriesDao().getAllCategories()
categoriesAdapter!!.setData(categories)
arrCategories = categories as ArrayList<Categories>
binding.recyclerView.adapter = categoriesAdapter
}
}
categoriesAdapter!!.setOnClickListener(onClicked)
}
private val onClicked = object : CategoriesAdapter.OnItemClickListener{
override fun onClicked(categoriesId: Int) {
var fragment = NotOlustur()
var bundle = Bundle()
bundle.putInt("categoriesId",categoriesId)
fragment.arguments = bundle
findNavController().navigate(R.id.action_kategoriler_to_notlar, bundle)
}
}
}
Meanwhile i am working with 2 databases. I solve the issues about databases. My second database and adapter almost has the same code syntax. The first one is working well but the second one, i am getting this error. I did everything exactly the same, just changed the names. I dont know why i got this error.