kotlin:error in Fragment when adding the cardstackview in a tinder like app - kotlin

Question

I am following this tutorial about how to make a Tinder like app with Kotlin and using the third library CardStackView :
https://www.simplifiedcoding.net/tinder-like-swipe-cards-android/
However ,in my case ,shows up an error as follow:
Attempt to invoke virtual method 'void com.yuyakaido.android.cardstackview.CardStackView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference
at com.gearsrun.stackviewapplication.UI.Home.HomePageFragment.onCreateView(HomePageFragment.kt:36)
HomeUserAdapter.kt:
package com.gearsrun.stackviewapplication.HomeUserClass
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import com.gearsrun.stackviewapplication.R
import com.squareup.picasso.Picasso
import kotlinx.android.synthetic.main.user_card.view.*
class HomeUserAdapter:RecyclerView.Adapter<HomeUserAdapter.HomeUserViewHolder>() {
private var homeUserList:List<HomeUserItem>?=null
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): HomeUserViewHolder {
val itemView = LayoutInflater.from(parent.context).inflate(R.layout.user_card,parent,false)
return HomeUserViewHolder(itemView)
}
override fun onBindViewHolder(holder: HomeUserViewHolder, position: Int) {
val homeUserList = generateUser()
val currentItem = homeUserList[position]
Picasso.get().load(currentItem.user_img).into(holder.user_img)
holder.user_name.text = currentItem.user_name
holder.medal_num.text = currentItem.medal_num
holder.id_num.text = currentItem.userId
holder.user_intro.text = currentItem.user_intro
holder.user_give_num.text = currentItem.user_give_num
holder.user_receive_num.text = currentItem.user_receive_num
}
private fun generateUser(): ArrayList<HomeUserItem> {
val list = ArrayList<HomeUserItem>()
list.add(
HomeUserItem(
"https://i.pinimg.com/236x/8c/64/03/8c6403cc892231f15a6845e00d7433a9.jpg",
"Maria",
"200",
"510uu",
"I am from USA ,I am an engineer ,I hope to make the world a better place",
"500",
"100")
)
)
return list
}
override fun getItemCount(): Int {
return homeUserList!!.size
}
class HomeUserViewHolder(itemView: View):RecyclerView.ViewHolder(itemView) {
val user_img : ImageView = itemView.user_img
val user_name : TextView = itemView.user_name
val medal_num : TextView = itemView.medal_num
val id_num : TextView = itemView.id_num
val user_intro : TextView = itemView.user_intro
val user_give_num : TextView = itemView.user_give_num
val user_receive_num : TextView = itemView.user_receive_num
}
}
HomePageFragment.kt
package com.gearsrun.stackviewapplication.UI.Home
import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.view.animation.LinearInterpolator
import androidx.recyclerview.widget.DefaultItemAnimator
import com.gearsrun.stackviewapplication.HomeUserClass.HomeUserAdapter
import com.gearsrun.stackviewapplication.HomeUserClass.HomeUserItem
import com.gearsrun.stackviewapplication.R
import com.yuyakaido.android.cardstackview.CardStackLayoutManager
import com.yuyakaido.android.cardstackview.CardStackListener
import com.yuyakaido.android.cardstackview.Direction
import com.yuyakaido.android.cardstackview.SwipeableMethod
import kotlinx.android.synthetic.main.fragment_home_page.*
class HomePageFragment : Fragment(),CardStackListener {
private lateinit var layoutManager: CardStackLayoutManager
private val adapter = HomeUserAdapter()
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val v = inflater.inflate(R.layout.fragment_home_page, container, false)
// v.rv_UserHome.layoutManager = LinearLayoutManager(context,LinearLayoutManager.VERTICAL,false)
layoutManager = CardStackLayoutManager(context,this).apply {
setSwipeableMethod(SwipeableMethod.AutomaticAndManual)
setOverlayInterpolator(LinearInterpolator())
}
stack_view.layoutManager = layoutManager
stack_view.adapter = adapter
stack_view.itemAnimator.apply {
if(this is DefaultItemAnimator){
supportsChangeAnimations = false
}
}
return v
}
override fun onCardDragging(direction: Direction?, ratio: Float) {
TODO("Not yet implemented")
}
override fun onCardSwiped(direction: Direction?) {
TODO("Not yet implemented")
}
override fun onCardRewound() {
TODO("Not yet implemented")
}
override fun onCardCanceled() {
TODO("Not yet implemented")
}
override fun onCardAppeared(view: View?, position: Int) {
TODO("Not yet implemented")
}
override fun onCardDisappeared(view: View?, position: Int) {
TODO("Not yet implemented")
}
}
Could you please help me take a look my code ?
Thank you so much in advance !

Answer 1

Move all that layoutManager and stackView stuff from onCreate to onViewCreated because during onCreate your view is not created yet and same is assured in onViewCreated.
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
layoutManager = CardStackLayoutManager(context,this).apply {
setSwipeableMethod(SwipeableMethod.AutomaticAndManual)
setOverlayInterpolator(LinearInterpolator())
}
stack_view.layoutManager = layoutManager
stack_view.adapter = adapter
stack_view.itemAnimator.apply {
if(this is DefaultItemAnimator){
supportsChangeAnimations = false
}
}
}
or you can refer here