creat viewholder and adapter for group

app/build.gradle

@@ -53,6 +53,9 @@ dependencies {
 // Material design
     implementation "com.google.android.material:material:$rootProject.materialVersion"
 
+    implementation 'com.thoughtbot:expandablerecyclerview:1.3'
+    implementation 'com.thoughtbot:expandablecheckrecyclerview:1.4'
+
 // Testing
     testImplementation 'junit:junit:4.12'
     androidTestImplementation "androidx.arch.core:core-testing:$rootProject.coreTestingVersion"

app/src/main/java/com/developer/kulloveth/expandablelistsamplewithroom/data/MainViewHoder.kt

@@ -0,0 +1,26 @@
+package com.developer.kulloveth.expandablelistsamplewithroom.data
+
+import android.view.View
+import android.widget.TextView
+import com.developer.kulloveth.expandablelistsamplewithroom.R
+import com.developer.kulloveth.expandablelistsamplewithroom.data.model.Continents
+import com.developer.kulloveth.expandablelistsamplewithroom.data.model.Countrys
+import com.thoughtbot.expandablerecyclerview.viewholders.ChildViewHolder
+import com.thoughtbot.expandablerecyclerview.viewholders.GroupViewHolder
+
+
+class CountryViewHolder(itemView: View) : ChildViewHolder(itemView) {
+    val countryName = itemView.findViewById<TextView>(R.id.countryName)
+
+    fun bind(countrys: Countrys) {
+        countryName.text = countrys.countryName
+    }
+}
+
+class ContinentViewHolder(itemView: View) : GroupViewHolder(itemView) {
+    val continentName = itemView.findViewById<TextView>(R.id.continent)
+
+    fun bind(continent: Continents) {
+        continentName.text = continent.ContinentName
+    }
+}

app/src/main/java/com/developer/kulloveth/expandablelistsamplewithroom/data/model/Continents.kt

@@ -4,9 +4,12 @@ import android.os.Parcelable
 import androidx.room.ColumnInfo
 import androidx.room.Entity
 import androidx.room.PrimaryKey
+import com.thoughtbot.expandablerecyclerview.models.ExpandableGroup
 import kotlinx.android.parcel.Parcelize
 
-@Parcelize
+
 @Entity(tableName = "continent-table")
-data class Continents(@PrimaryKey @ColumnInfo(name = "continent")val ContinentName: String,
-                      @ColumnInfo(name = "countrys")val countrys: List<Countrys>) : Parcelable
+data class Continents(
+    @PrimaryKey @ColumnInfo(name = "continent") val ContinentName: String,
+    @ColumnInfo(name = "countrys__layout") val countrys: List<Countrys>
+) : ExpandableGroup<Countrys>(ContinentName, countrys)

app/src/main/java/com/developer/kulloveth/expandablelistsamplewithroom/data/ui/ContinentAdapter.kt

@@ -0,0 +1,50 @@
+package com.developer.kulloveth.expandablelistsamplewithroom.data.ui
+
+import android.view.LayoutInflater
+import android.view.ViewGroup
+import android.widget.ExpandableListAdapter
+import com.developer.kulloveth.expandablelistsamplewithroom.R
+import com.developer.kulloveth.expandablelistsamplewithroom.data.ContinentViewHolder
+import com.developer.kulloveth.expandablelistsamplewithroom.data.CountryViewHolder
+import com.developer.kulloveth.expandablelistsamplewithroom.data.model.Continents
+import com.developer.kulloveth.expandablelistsamplewithroom.data.model.Countrys
+import com.thoughtbot.expandablerecyclerview.ExpandableRecyclerViewAdapter
+import com.thoughtbot.expandablerecyclerview.models.ExpandableGroup
+
+class ContinentAdapter(groups: List<ExpandableGroup<*>>?) :
+    ExpandableRecyclerViewAdapter<ContinentViewHolder, CountryViewHolder>(
+        groups
+    ) {
+
+
+    override fun onCreateGroupViewHolder(parent: ViewGroup?, viewType: Int): ContinentViewHolder {
+        val itemView =
+            LayoutInflater.from(parent?.context).inflate(R.layout.continent_layout, parent, false)
+        return ContinentViewHolder(itemView)
+    }
+
+    override fun onCreateChildViewHolder(parent: ViewGroup?, viewType: Int): CountryViewHolder {
+        val itemView =
+            LayoutInflater.from(parent?.context).inflate(R.layout.countrys_layout, parent, false)
+        return CountryViewHolder(itemView)
+    }
+
+    override fun onBindChildViewHolder(
+        holder: CountryViewHolder?,
+        flatPosition: Int,
+        group: ExpandableGroup<*>?,
+        childIndex: Int
+    ) {
+        val countrys: Countrys = group?.items?.get(childIndex) as Countrys
+        holder?.bind(countrys)
+    }
+
+    override fun onBindGroupViewHolder(
+        holder: ContinentViewHolder?,
+        flatPosition: Int,
+        group: ExpandableGroup<*>?
+    ) {
+        val continents: Continents = group as Continents
+        holder?.bind(continents)
+    }
+}

app/src/main/java/com/developer/kulloveth/expandablelistsamplewithroom/data/ui/MainActivity.kt

@@ -3,11 +3,13 @@ package com.developer.kulloveth.expandablelistsamplewithroom.data.ui
 import androidx.appcompat.app.AppCompatActivity
 import android.os.Bundle
 import com.developer.kulloveth.expandablelistsamplewithroom.R
+import kotlinx.android.synthetic.main.activity_main.*
 
 class MainActivity : AppCompatActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
+
     }
 }

app/src/main/res/layout/activity_main.xml

@@ -6,10 +6,10 @@
     android:layout_height="match_parent"
     tools:context=".data.ui.MainActivity">
 
-    <TextView
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:text="Hello World!"
+    <androidx.recyclerview.widget.RecyclerView
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:id="@+id/rvConinent"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintLeft_toLeftOf="parent"
         app:layout_constraintRight_toRightOf="parent"

app/src/main/res/layout/countrys.xml → app/src/main/res/layout/countrys_layout.xml

@@ -5,7 +5,7 @@
     android:orientation="vertical">
 
     <TextView
-        android:id="@+id/country"
+        android:id="@+id/countryName"
         android:layout_width="match_parent"
         android:layout_height="wrap_content" />