kotlin recyclerview data not showing

问题:

Our question is how to show Parent and Child data from two SQLite DB tables?

We have two tables that are added to two ArrayLists childList and parentList.

Here are the Model Class's for each

class ModelParent {
    var idD:Int = 0
    var dept:String = ""
    var fkD:Int = 0
    var children: List<ModelChild> = mutableListOf()
    //var children: ArrayList<ModelChild>? = null
    //var children: List<ModelChild>  by Delegates.notNull()
    constructor (children: List<ModelParent>) : this()
    companion object {
       var globalVar = 1
   }
}

class ModelChild {
    var idI:Int = 0
    var item:String = ""
    var fkI:Int = 0
}

We have two Adapters for each table and will post that code
We are able to iterate through the two ArrayList with this code and display the data in the format we would like to show in the ViewActivity.

fun theGET(){
    val db = DBHelper(this)
    childList = db.queryITEM()
    parentList = db.queryDEPT()
    var PL = parentList.size

    do {
        var DEPT: String = parentList[z].dept
        var PARENT_LIST_FK = parentList.get(z).fkD
            println("========== Dept " + DEPT + " fkD " + PARENT_LIST_FK)
        val FK = PARENT_LIST_FK
        childList = db.queryALL(FK)
        var CL = childList.size
        for (a in 0..CL - 1) {
            var CHILD_ITEM = childList[a].item
            var CHILD_LIST_FK = childList[a].fkI
            println("========== item " + CHILD_ITEM+" fkI "+CHILD_LIST_FK)
        }
        z++
    }
    while (z <= PL-1)
}

We will post the View Activity

class ViewActivity : AppCompatActivity() {
    lateinit var recyclerView: RecyclerView

    private var parentList:List<ModelParent> = ArrayList()
    private var childList:List<ModelChild> = ArrayList()

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

        initRecycler()

    }// end onCreate

    private fun initRecycler() {
        val db = DBHelper(this)
        childList = db.queryITEM()
        parentList = db.queryDEPT()

        recyclerView = rv_parent

        recyclerView.apply{
            layoutManager = LinearLayoutManager(this@ViewActivity, LinearLayout.VERTICAL, false)
            adapter = ViewAdapter(parentList)
            adapter = ViewChildAdapter(children = childList)
        }
    }
}

ViewActivity has this XML file

<?xml version="1.0" encoding="utf-8"?>
<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"
    tools:context=".ViewActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_parent"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</android.support.constraint.ConstraintLayout>

The Two Adapters and coresponding XML files

class ViewAdapter(private val parents:List<ModelParent>):RecyclerView.Adapter<ViewAdapter.ViewHolder>() {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.the_view,parent,false)
        return ViewHolder(view)
    }

    override fun getItemCount(): Int {
        return parents.size
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val parent = parents[position]
        holder.textView.text = parent.dept
        holder.recyclerView.apply {
            layoutManager = LinearLayoutManager(holder.recyclerView.context, LinearLayout.VERTICAL, false) as RecyclerView.LayoutManager?
            adapter = ViewChildAdapter(parent.children!!)
        }
    }

    inner class ViewHolder(itemView : View) : RecyclerView.ViewHolder(itemView){
        val recyclerView : RecyclerView = itemView.rv_child
        val textView: TextView = itemView.textView
    }
}

class ViewChildAdapter(private val children:List<ModelChild>):RecyclerView.Adapter<ViewChildAdapter.ViewHolder>() {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.child_recycler,parent,false)
        return ViewHolder(view)
    }
    override fun getItemCount(): Int {
        return children.size
    }
    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val child = children[position]
        holder.textView.text = child.item
    }

    inner class ViewHolder(itemView : View) : RecyclerView.ViewHolder(itemView){
        val textView : TextView = itemView.child_textView
    }
}

Inflated XML files

<android.support.v7.widget.CardView 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/card_view"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:layout_margin="2dp"
    card_view:cardBackgroundColor="#fff"
    card_view:cardCornerRadius="5dp"
    card_view:cardElevation="4dp"
    card_view:cardUseCompatPadding="true">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <TextView
            android:id="@+id/textView"
            style="@style/Base.TextAppearance.AppCompat.Subhead"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignStart="@+id/rv_child"
            android:layout_alignParentTop="true"
            android:padding="20dp"
            android:background="@color/color_super_lightGray"
            android:text="Dept Header"
            android:textColor="@color/color_Purple"
            android:textSize="24sp"
            android:textStyle="bold" />

        <android.support.v7.widget.RecyclerView
            android:id="@+id/rv_child"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            android:layout_alignParentBottom="true"
            android:layout_marginTop="70dp"
            android:layout_marginBottom="0dp"
            android:orientation="horizontal"
            android:paddingLeft="4dp"
            android:paddingTop="8dp"
            tools:layout_editor_absoluteX="74dp" />
    </RelativeLayout>
</android.support.v7.widget.CardView>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="horizontal"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <TextView
        android:id="@+id/child_textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginStart="32dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        android:background="@color/color_Transparent"
        android:padding="10dp"
        android:text="TextView"
        android:textColor="@color/color_Black"
        android:textSize="20sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />

When the ViewActivity is loaded ONLY the childList is displayed.

We have tried various changes and can not display the parent List though using theGET fun the parentList data is displayed so we know it is in the list.

We can run the fun theGET and crate a new ArrayList that seems futile.

Our concern is that the parentList is displayed and then removed when the childList is displayed.

We do not know how to prove this.

So our question is how to show Parent and Child data in a organized fashion in the View Activity?

We are adding New CODE based on @Cruces answer
Some issues with this code are beyond out understanding
1. We have no way to run the fun join to create the newList
2. Parent and Child ViewHolder can be called only with receiver of containing Class
3. Too many inner Class's and do we need an Outer Nested annotation?
4. or if both parent and child implement an interface a List< IItem > )
We do not know how to write an interface and connect it to the JoinAdapter

While the answer poses new question we feel it better to ask with in this context = Context HUMOR Here is the FIX for the JoinAdapter

class JoinAdapter(internal var context: Context, val parents: List<ModelParent>) : RecyclerView.Adapter<JoinAdapter.MyViewHolder>() {
val items = mutableListOf<Any>()

init {
    parents //parents should be passed as a constructor argument
            .forEach {
                items.add(it)
                items.addAll(it.children)
            }
}

override fun getItemCount(): Int = items.size;


fun getItem(position: Int): Any = items[position]

override fun getItemViewType(position: Int): Int = if (getItem(position) is ModelParent) 0 else 1

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
    var view: View? = null
    if (viewType == 0) {
        view = LayoutInflater.from(parent.context).inflate(R.layout.the_view, parent, false)
        return ParentViewHolder(view!!)
    } else {
        view = LayoutInflater.from(parent.context).inflate(R.layout.child_recycler, parent, false)
        return ChildViewHolder(view!!)
    }
}

override fun onBindViewHolder(holder: MyViewHolder, position: Int) = holder.bindData(position, getItem(position))

inner abstract class MyViewHolder(view: View) : RecyclerView.ViewHolder(view) {
    abstract fun bindData(position: Int, item: Any)

}

inner class ParentViewHolder(view: View) : MyViewHolder(view) {
    override fun bindData(position: Int, item: Any) {
        val parent = item as? ModelParent ?: return
        parent.dept
        parent.fkD
        parent.children
        //bind the data here
    }

    init {
        val textView: TextView = view.textView
        var editCLICK: RelativeLayout = view.findViewById(R.id.editCLICK) as RelativeLayout
        //do the view setup here
    }

}

inner class ChildViewHolder(view: View) : MyViewHolder(view) {
    init {
        val textView : TextView = itemView.child_textView
        //do the view setup here
    }

    override fun bindData(position: Int, item: Any) {
        val child = item as? ModelChild ?: return
        child.item
        child.idI
        //bind the data here
    }
}

I am going to post the View Activity call to Join Adapter
Code does not FAIL it just shows nothing?

        RecyclerAdapter1 = JoinAdapter(parents = ArrayList(),context = applicationContext)
    (recyclerView as RecyclerView).adapter = RecyclerAdapter1

Here is the ViewJoinActivity it will load the Parent Data NO Child Data

class ViewJoinActivity : AppCompatActivity() {

lateinit var recyclerView: RecyclerView
private var RecyclerAdapter: JoinAdapter? = null
private var linearLayoutManager: LinearLayoutManager? = null
private val db = DBHelper(this)
private var parentList:List<ModelParent> = ArrayList()
private var childList:List<ModelChild> = ArrayList()

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

}// end onCreate

override fun onResume() {
    super.onResume()
    initDB()
}

private fun initDB() {
    parentList = db.queryDEPT()
    //childList = db.queryCHILD(1)
    childList = db.queryITEM()
    // queryCHILD only selects records with a fkI equal to idD
    // SEE THE ModelChild and ModelParent
    if(parentList.isEmpty()){
        title = "No Records in DB"
    }else{
        title = "Parent List"
    }

        RecyclerAdapter = JoinAdapter(parents = parentList, context = applicationContext)
        (recyclerView as RecyclerView).adapter = RecyclerAdapter
    }

private fun initRecycler() {
    val db = DBHelper(this)
    childList = db.queryITEM()
    parentList = db.queryDEPT()

    //recyclerView = rv_parent

    /*var PL = parentList.size
    newList.clear()
    do {
        var DEPT: String = parentList[z].dept
        var ND:String = DEPT
        var PARENT_LIST_FK = parentList.get(z).fkD
        var PL_ST = ND+" "+PARENT_LIST_FK
        newList.add(PL_ST)

        println("========== Dept " + DEPT + " fkD " + PARENT_LIST_FK)
        val FK = PARENT_LIST_FK

        childList = db.queryCHILD(FK)
        var CL = childList.size

        for (a in 0..CL - 1) {
            var CHILD_ITEM = childList[a].item
            var NI:String = childList[a].item
            var CHILD_LIST_FK = childList[a].fkI
            var IL_ST = NI+" "+CHILD_LIST_FK
            newList.add(IL_ST)
            println("========== item " + CHILD_ITEM+" fkI "+CHILD_LIST_FK)
        }
        z++

        g++
    }
    while (z <= PL-1)


    var ui = newList.size
    g=0
    for(g in 0..ui-1){
        var N2 = newList[g]

        if(N2.toString().contains("1")){
            println("********************** We Found "+N2)

        }
        println("############### BOTH = "+N2)

    }*/

    recyclerView = this.findViewById(R.id.rv_parent)
    RecyclerAdapter = JoinAdapter(parents = parentList, context = applicationContext)
    linearLayoutManager = LinearLayoutManager(applicationContext)
    (recyclerView as RecyclerView).layoutManager = linearLayoutManager!!

    //recyclerView.apply {
        //layoutManager = LinearLayoutManager(this@ViewJoinActivity, LinearLayout.VERTICAL, false)
        //adapter = JoinAdapter(children = childList)
    //}

}

}

Calling the Join Adapter from a Activity is the issue? ? This Activity has a XML associated file with a RecyclerView rv_parent

回答1:

The way I would do it is flatten the list edit: like this in the constructor

val items : MutableList<Any> = mutableListOf<Any>()    

init() {
   parents //parents should be passed as a constructor argument
         .asSequence() //this is only needed if you want to also order them
         .sortedBy { it.idD } //again only if you want to sort them
         .forEach { 
              items.add(it)
              items.addAll(it.children)
          }
}

I would create a List < Any > (or if both parent and child implement an interface a List< IItem > ) that would contain all the data as you wish to see it, so for example it could look like this:

val items : List<Any> = listOf(parent1, child11,child12,child13,parent2,child12,child13,child14.....etc)

then I would implement a single adapter with multiple view types like this:

override fun getItemCount(): Int {
    return items.size
}

fun getItem(position: Int) : Any { //or the interface 
    return items[position]
}

override getItemViewType (position: Int) : Int {
    if (getItem(position) is ModelParent)
        return 0
    return 1
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
    var view : View? = null
    if (viewType == 0) {
        view = LayoutInflater.from(parent.context).inflate(R.layout.parent_layout,parent,false)
        return ParentViewHolder(view);
    } else {
       view = LayoutInflater.from(parent.context).inflate(R.layout.child_layout,parent,false)
        return ChildViewHolder(view);
    }
}

and then I would use two view holders to represent how the data is shown for the specific item

 inner class ParentViewHolder(itemView : View) : RecyclerView.ViewHolder(itemView){ ...}
 inner class ChildViewHolder(itemView : View) : RecyclerView.ViewHolder(itemView){ ...}

after that I could perform different bindings by getting the type of the view ,something like this:

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    if (getItemType(position) == 0) {
        (holder as ParentViewHolder).bindData(....)
    } else {
        (holder as ChildViewHolder).bindData(....)
    }
}

edit: Here is the complete adapter I built, it is based on two layout files:

list_item_child:

<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/card_view"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:layout_margin="2dp"
    card_view:cardBackgroundColor="#fff"
    card_view:cardCornerRadius="5dp"
    card_view:cardElevation="4dp"
    card_view:cardUseCompatPadding="true">

    <TextView
        android:id="@+id/child_item"
        style="@style/Base.TextAppearance.AppCompat.Display3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:padding="20dp"
        android:textSize="24sp"
        android:textStyle="bold"
        tools:text="Dept Header" />

</android.support.v7.widget.CardView>

list_item_parent:

<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/card_view"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:layout_margin="2dp"
    card_view:cardBackgroundColor="#fff"
    card_view:cardCornerRadius="5dp"
    card_view:cardElevation="4dp"
    card_view:cardUseCompatPadding="true">

    <TextView
        android:id="@+id/parent_department"
        style="@style/Base.TextAppearance.AppCompat.Headline"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:padding="20dp"
        tools:text="Dept Header"
        android:textSize="24sp"
        android:textStyle="bold" />

</android.support.v7.widget.CardView>

and the adapter would look something like this:

import android.content.Context
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView

data class ModelParent(val id: Int, val children: List<ModelChild>)
data class ModelChild(val id: Int)


class JoinAdapter(internal var context: Context, val parents: List<ModelParent>) : RecyclerView.Adapter<JoinAdapter.MyViewHolder>() {
    val items = mutableListOf<Any>()

    init {
        parents //parents should be passed as a constructor argument
                .forEach {
                    items.add(it)
                    items.addAll(it.children)
                }
    }

    override fun getItemCount(): Int = items.size;


    fun getItem(position: Int): Any = items[position]

    override fun getItemViewType(position: Int): Int = if (getItem(position) is ModelParent) 0 else 1

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        var view: View? = null
        if (viewType == 0) {
            view = LayoutInflater.from(parent.context).inflate(R.layout.rv_list_item_parent, parent, false)
            return ParentViewHolder(view!!)
        } else {
            view = LayoutInflater.from(parent.context).inflate(R.layout.rv_list_item_child, parent, false)
            return ChildViewHolder(view!!)
        }
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) = holder.bindData(position, getItem(position))

    inner abstract class MyViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        abstract fun bindData(position: Int, item: Any)

    }

    inner class ParentViewHolder(view: View) : MyViewHolder(view) {
        var parentDept: TextView = view.findViewById(R.id.parent_department) as TextView

        override fun bindData(position: Int, item: Any) {
            val parent = item as? ModelParent ?: return
            parentDept.text = parent.dept
        }
    }

    inner class ChildViewHolder(view: View) : MyViewHolder(view) {
        var childItem: TextView = view.findViewById(R.id.child_item) as TextView

        override fun bindData(position: Int, item: Any) {
            val child = item as? ModelChild ?: return
            childItem.text = child.item
        }
    }

}

this when used on a single recyclerview will display all children under their parent in a list

回答2:

Here is a answer and some observations about the design of this app
The answer does NOT place both the parent and child data on the same Recycler View List
But the answer may help to solve the issue With further exploration!
What we did was create the parent list and when the Parent Dept is clicked on the corresponding Child Items will be displayed. This may be a more functional design while shopping you only need to look at Produce items while in that section. This means less scrolling through a single master list of Parents and Children.

A word or two about the design we are guessing a grocery store might have 20 or more Departments (Parents) so how you plan to know which Items (Child data) is connected to the appropriate Dept (Parent) needs drastic redesign when building these two lists.

If you downloaded the code from GitHub you will have a better grasp about this design deficiency

Here is all the code with the XML files

Main Activity navigates to View Activity

    fun onViewAll(view: View){
    val intent = Intent(this,ViewActivity::class.java)
    intent.putExtra("pickADAPTER",2)
    startActivity(intent)
}

Here is the View Activity

class ViewActivity : AppCompatActivity() {

lateinit var recyclerView: RecyclerView

private var RecyclerAdapter1: ViewAdapter? = null
private var RecyclerAdapter2: ViewChildAdapter? = null
private var linearLayoutManager: LinearLayoutManager? = null

private val db = DBHelper(this)

private var parentList:List<ModelParent> = ArrayList()
private var childList:List<ModelChild> = ArrayList()

var idD = 0
var whichADAPTER = 0

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_view)
    val bundle: Bundle = intent.extras
    idD = bundle.getInt("BIGi", 0)
    whichADAPTER = bundle.getInt("pickADAPTER",0)

    initRecycler()

}// end onCreate

override fun onResume() {
    super.onResume()
    initDB()
}

private fun initDB() {
    parentList = db.queryDEPT()
    childList = db.queryCHILD(idD)
    // queryCHILD only selects records with a fkI equal to idD
    // SEE THE ModelChild and ModelParent
    if(parentList.isEmpty()){
        title = "No Records in DB"
    }else{
        title = "Parent List"
    }

    if(whichADAPTER == 2) {
        RecyclerAdapter1 = ViewAdapter(parents = parentList, context = applicationContext)
        (recyclerView as RecyclerView).adapter = RecyclerAdapter1
    }else{
        RecyclerAdapter2 = ViewChildAdapter(children = childList)
        (recyclerView as RecyclerView).adapter = RecyclerAdapter2
    }
}

private fun initRecycler() {
    val db = DBHelper(this)
    childList = db.queryITEM()
    parentList = db.queryDEPT()

    recyclerView = rv_parent

    recyclerView = this.findViewById(R.id.rv_parent)
    RecyclerAdapter1 = ViewAdapter(parents = parentList, context = applicationContext)
    linearLayoutManager = LinearLayoutManager(applicationContext)
    (recyclerView as RecyclerView).layoutManager = linearLayoutManager!!

}

Here the XML file for View Activity

<android.support.v7.widget.RecyclerView
android:id="@+id/rv_parent"
android:layout_width="match_parent"
android:layout_height="match_parent" />

Here is the View Adapter

class ViewAdapter(private val parents: List<ModelParent>, internal var context: Context):RecyclerView.Adapter<ViewAdapter.ViewHolder>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
    val view = LayoutInflater.from(parent.context).inflate(R.layout.the_view,parent,false)
    return ViewHolder(view)
}

override fun getItemCount(): Int {
    return parents.size
}

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    val parent = parents[position]
    holder.textView.text = parent.dept

    holder.editCLICK.setOnClickListener {
        val i = Intent(context, ViewActivity::class.java)
        i.putExtra("BIGi",parent.idD)
        i.flags = Intent.FLAG_ACTIVITY_NEW_TASK
        context.startActivity(i)
    }
}

inner class ViewHolder(itemView : View) : RecyclerView.ViewHolder(itemView){
    //val recyclerView : RecyclerView = itemView.rv_child
    val textView: TextView = itemView.textView
    var editCLICK: RelativeLayout = itemView.findViewById(R.id.editCLICK) as 
    RelativeLayout

And the inflated XML

<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/card_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_margin="2dp"
card_view:cardBackgroundColor="#FF0000"
card_view:cardCornerRadius="5dp"
card_view:cardElevation="4dp"
card_view:cardUseCompatPadding="true">

<RelativeLayout
    android:id="@+id/editCLICK"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textView"
        style="@style/Base.TextAppearance.AppCompat.Subhead"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/rv_child"
        android:layout_alignParentTop="true"
        android:padding="10dp"
        android:background="@color/color_lightGray"
        android:text="Dept Header"
        android:textColor="@color/color_Purple"
        android:textSize="24sp"
        android:textStyle="bold" />

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_child"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_alignParentBottom="true"
        android:layout_marginTop="50dp"
        android:layout_marginBottom="0dp"
        android:orientation="horizontal"
        android:paddingLeft="4dp"
        android:paddingTop="6dp"
        tools:layout_editor_absoluteX="74dp" />

</RelativeLayout>

This is the search routine in DBHelper

    fun queryCHILD(fkI: Int): List<ModelChild> {
    val db = this.writableDatabase
    val childList = ArrayList<ModelChild>()
    val selectQuery = "SELECT  * FROM $CHILD_TABLE WHERE $colCFK = ?"
    val cursor = db.rawQuery(selectQuery, arrayOf(fkI.toString()))
    if (cursor != null) {
        if (cursor.moveToFirst()) {
            do {
                val contact = ModelChild()
                contact.idI = Integer.parseInt(cursor.getString(cursor.getColumnIndex(colidI)))
                contact.item = cursor.getString(cursor.getColumnIndex(colItem))
                contact.fkI = Integer.parseInt(cursor.getString(cursor.getColumnIndex(colCFK)))
                childList.add(contact)
            } while (cursor.moveToNext())
        }
    }
    cursor.close()
    return childList
}

One thing to make note of we attached the OnClickListener to a Relative Layout

 holder.editCLICK.setOnClickListener

Why we are not sure you can obtain parent.idD type information from a RecyclerView set as a listener?
We need to explore this but in our testing the code failed when we tried.

回答3:

In the ViewActivity class, you have first set the recyclerView adapter to ViewAdapter and then to ViewChildAdapter thus, now, the adapter of recyclerView is ViewChildAdapter instead of ViewAdapter. Remove this line and the problem will be resolved.