IllegalStateException: RecyclerView is null inside of Fragment within NavigationDrawer activity

Question

I tried to make a RecyclerView that will go inside one of the two pages of my fragments. These pages are put inside a NavigationDrawer activity. The goal is to create something like the Play Store app homepage.

But I found an error in this snippet of code on runtime. It says:

java.lang.IllegalStateException: mainMenu must not be null
    at com.example.MyApp.app.fragment.MainFragment.onCreate(MainFragment.kt:49)

Ive been looking at some SO threads, and they said that the layouts are not properly loaded. Which caused some elements not linked as it should. Another said in the comments that the problem is with the context not initialized properly. Which is not the case for me (rather it's the RecyclerView).

Here are the links, hope they could be useful as a reference.

After multiple-checks on my codes, I swear I've put the right layouts in. EDIT: I imported the kotlinx.android.synthetic.main.^ package where I put this sign: ^${layout}. Here's some of my files (forgive me if this thread becomes too long):

MainActivity.kt : AppCompatActivity() ^activity_main.*

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

        // preparing the app bars
        setSupportActionBar(toolBar)

        // getting ready for the pages
        val pagerAdapter = MainPagerAdapter(
                supportFragmentManager,
                resources.getString(R.string.tab_main),
                resources.getString(R.string.tab_chat)
        )
        pager.adapter = pagerAdapter

        // activating tabs
        tabLayout.setupWithViewPager(pager)

        val toggle = ActionBarDrawerToggle(
                this, mainDrawer, toolbar,
                R.string.navigation_drawer_open,
                R.string.navigation_drawer_close)

        mainDrawer.addDrawerListener(toggle)


        navView.setNavigationItemSelectedListener(this)
        toggle.syncState()

}

MainPagerAdapter.kt (fm: FragmentManager, private val page1: String, private val page2: String): FragmentPagerAdapter(fm)

override fun getItem(position: Int): Fragment? {
    return when (position) {
        0 -> MainFragment()
        1 -> ChatFragment()
        else -> null
    }
}

override fun getCount() = 2

override fun getPageTitle(position: Int): CharSequence? {
    return when (position) {
        0 -> page1
        1 -> page2
        else -> null
    }
}

MainFragment.kt : Fragment() ^content_main.*

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?)
    : View? = inflater.inflate(R.layout.content_main, container)

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    // this is the error
    mainMenu.layoutManager = LinearLayoutManager(this.context)

    mainMenu.adapter = MyAdapter(itemList) {
        toast("${it.name} selected")
    }
}

MyAdapter.kt: RecyclerView.Adapter<MyAdapter.MyHolder>() ^item_custom.view.*(courtesy of Antonio Leiva)

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int)
    = GoodsHolder(parent.inflate(R.layout.item_custom))

override fun getItemCount()
    = itemList.size

override fun onBindViewHolder(holder: MyHolder, position: Int)
    = holder.bind(itemList[position], listener)


class MyHolder(v: View): RecyclerView.ViewHolder(v){
    private val item: Item? = null
    private val view = v

    fun bind(item: Item, listener: (Item) -> Unit)
            = with (itemView) {
        imgPic.setImageResource(item.pictureId)
        txtName.text = item.name
        txtPrice.text = item.price.toString()

    setOnClickListener { listener(item) }
    }
}

content_main.xml

<android.support.constraint.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"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.example.MyApp.app.activity.MainActivity"
    >

    <!-- the RecyclerView that caused the runtime error -->
    <android.support.v7.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/mainMenu"/>

</android.support.constraint.ConstraintLayout>

item_custom.xml (These code are inside a LinearLayout inside a CardView)

<ImageView
    android:id="@+id/imgPic"
    android:layout_width="match_parent"
    android:layout_height="128dp"
    app:srcCompat="@drawable/ic_menu_gallery" />

<TextView
    android:id="@+id/txtName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Get it while it's hot!"
    android:layout_margin="@dimen/margin_small"
    android:layout_marginTop="@dimen/margin_medium"
    android:maxLines="2"
    android:ellipsize="end"
    android:textStyle="bold"
    />

<TextView
    android:id="@+id/txtPrice"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="$3.000.000"
    android:layout_marginLeft="@dimen/margin_small"
    android:layout_marginStart="@dimen/margin_small"
    android:layout_marginRight="@dimen/margin_small"
    android:layout_marginEnd="@dimen/margin_small"
    android:layout_marginBottom="@dimen/margin_medium"/>

ChatFragment.kt: Fragment() (only contains onCreateView inflating content_main_chat.xml)
content_main_chat.xml (only contains a TextView)

score 9 · Accepted Answer · answered Jan 26 '18 at 10:07

9

You have not initialized the RecyclerView in MainFragment.kt file. You have to initialize it before the below line:

mainMenu.layoutManager = LinearLayoutManager(this.context)

You can initialize the RecyclerView by the below line:

var mainMenu = findViewById(R.id.mainMenu) as RecyclerView

You have to change it as per your need.

answered Jan 26 '18 at 10:07

Avijit Karmakar

8,890
6
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I might need to point out that I use `kotlinx.android.synthetic.main.content_main.*` to be able to access the `mainMenu`. Is it possible that the Kotlin Android Extension failed to initialize my views? – hdx13_beatcode Jan 26 '18 at 12:53
Okay, so I initialized the RecyclerView under `OnCreateView()` instead, and then "initialize" (or smart cast) the RecyclerView by considering `if(inflatedView is RecyclerView)`. I just need to grab the context from that `inflatedView`. And finally it works as expected. – hdx13_beatcode Feb 13 '18 at 10:36
4

@hdx13_beatcode hey, can you explain what you mean? I am having the same issue right now – sourlemonaid Dec 29 '18 at 00:58

score 4 · Answer 2 · answered Aug 21 '18 at 04:03

For anyone that follow the brilliant clue of @Avijit Karmakar, getting in count another discussion, (RecyclerView error: No adapter attached; skipping layout) I had to include :

class WikiFragment : Fragment() {
    val paginas: ArrayList<String> = ArrayList()    

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
var listItems : View  = inflater.inflate(R.layout.fragment_wiki, container, false)

var rv_frag_wiki = listItems.findViewById<View>(R.id.rv_frag_wiki) as RecyclerView


 rv_frag_wiki.layoutManager = LinearLayoutManager(this.context)
        rv_frag_wiki.adapter = PaginasAdapter(paginas, this.context)
        
  return listItems

You should be able to use `findViewById` and skip the cast. – Aaron Frary Sep 11 '18 at 05:13 — Aaron Frary, Sep 11 '18 at 05:13

score 2 · Answer 3 · answered Jul 10 '19 at 15:02

Since you are using kotlin you can have advantage of synthetics where you don't need to do var rv_frag_wiki = listItems.findViewById<View>(R.id.rv_frag_wiki) as RecyclerView

Rather import synthetics via plugin Step 1 :

apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

Step 2 :

Import sythetic in MainFragment

import kotlinx.android.synthetic.main.content_menu.* //

Step 3 :

Finally in MainFragment

Shift this code of recyclerView here

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

        rvList.layoutManager = LinearLayoutManager(context, 
        LinearLayoutManager.VERTICAL, false)
        rvList.adapter = academyAdapter

    }

This is the correct answer, also the trick is use it inside onViewCreated — cflorenciav, Aug 20 '20 at 16:48

score 0 · Answer 4 · answered Jan 26 '18 at 10:02

0

You forgot to initialize your mainMenu inside onCreate of MainFragment.kt

answered Jan 26 '18 at 10:02

Benjamin

7,055
6
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score 0 · Answer 5 · answered Feb 12 '18 at 10:04

when you set your recyclerView's layoutManager

mainMenu.layoutManager = LinearLayoutManager(this.context)

this state your recyclerView has not been initialized so you have to initialize your recyclerView explicitly

val mainMenu = view.findViewById(R.id.recyclerView) as RecyclerView

score 0 · Answer 6 · answered Jan 12 '19 at 03:08

0

I think initialize the elements in onViewCreated is a better approach like @Egor Neliuba taught in: NullPointerException when trying to access views in a Kotlin fragment

answered Jan 12 '19 at 03:08

moralejaSinCuentoNiProverbio

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score 0 · Answer 7 · answered Jul 26 '20 at 21:29

  override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    val cardlist = generateDummyList(50)


    recycler_view.adapter = InfoAdapter(cardlist)
    recycler_view.layoutManager = LinearLayoutManager(context)

    recycler_view.setHasFixedSize(true)

}

Below link Worked in my case.

https://www.manongdao.com/q-596674.html

IllegalStateException: RecyclerView is null inside of Fragment within NavigationDrawer activity

7 Answers7