Update README.md

Update README.md

README.md

@@ -4,8 +4,103 @@
 [![License](https://img.shields.io/github/license/AdrianKuta/Expandable-RecyclerView?style=plastic)](https://github.com/AdrianKuta/Expandable-RecyclerView/blob/master/LICENSE)
 [![CircleCI](https://img.shields.io/circleci/build/github/AdrianKuta/Expandable-RecyclerView/master?label=CircleCI&style=plastic&logo=circleci)](https://circleci.com/gh/AdrianKuta/Expandable-RecyclerView)
 
-Library is currently during implementation! It is **not** ready to use yet :/
+With this adapter you can add expand feature to regular RecyclerView.
 
-Final version will be released soon.
+All objects are store in [Tree (Data structure)](https://github.com/AdrianKuta/Tree-Data-Structure), so adapter can create multilevel expandable groups.
 
-![Release date](https://img.shields.io/date/1580493319?label=Expected%20release&style=for-the-badge)
+Under the hood, the tree is flattened to simple list, so from RecyclerView's point of view it can operate as usual.
+
+
+<img src="https://github.com/AdrianKuta/Expandable-RecyclerView/blob/master/Demo.gif" width="400" />
+
+## Download
+
+    implementation "com.github.adriankuta:expandable-recyclerView:$latest_versions"
+    
+## Usage
+To use expandable adapter we just have to expand our Adapter class with `ExpandableRecyclerViewAdapter<T, VH>`,
+where `T` is data type on which adapter will operate, `VH` is ViewHolder type.
+
+```kotlin
+class ExpandableAdapter: ExpandableRecyclerViewAdapter<String, RecyclerView.ViewHolder>() {
+    
+    
+    override fun getTreeNodes(): ExpandableTreeNode<String> {
+        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun onBindViewHolder(
+        holder: RecyclerView.ViewHolder,
+        treeNode: ExpandableTreeNode<String>,
+        nestLevel: Int
+    ) {
+        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun onCreateViewHolder(parent: ViewGroup, nestLevel: Int): RecyclerView.ViewHolder {
+        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
+    }
+}
+```    
+
+`ExpandableRecyclerViewAdapter` has build-in methods to control expandable groups:
+```kotlin
+fun toggleGroup(expandableTreeNode: ExpandableTreeNode<T>)
+
+fun expand(expandableTreeNode: ExpandableTreeNode<T>)
+
+fun collapse(expandableTreeNode: ExpandableTreeNode<T>)
+```
+
+Information if group is expanded or not is stored inside `ExpandableTreeNode` class
+
+
+### Creating tree
+
+There are different ways to create tree. The easiest way is to use extensions methods prepared specially for kotlin:
+
+```kotlin
+val tree = 
+    expandableTree("World") {
+        child("North America") {
+            child("USA")
+        }
+        child("Europe") {
+            child("Poland") {
+                child("Warsaw")
+            }
+            child("Germany")
+        }
+        child("Asia") {
+            child("China")
+        }
+    }
+```
+
+But in case when you want create tree at runtime, you can use `ExpandableTreeNode<T>` class to build tree:
+
+```kotlin
+val root = ExpandableTreeNode("World")
+val northA = ExpandableTreeNode("North America")
+val europe = ExpandableTreeNode("Europe")
+val asia = ExpandableTreeNode("Asia")
+
+root.addChild(northA)
+root.addChild(europe)
+root.addChild(asia)
+
+val poland = ExpandableTreeNode("Poland")
+europe.addChild(poland)
+// etc.
+```
+
+## Sample
+
+Full example of this library is available in app module.
+
+## Contribution
+
+Project is still during development and improvements.
+Issues with BUGs or suggestions are welcome.
+
+Also please feel free to fork library and contribute to project! ;-)

app/build.gradle

@@ -21,6 +21,9 @@ android {
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
         }
     }
+    dataBinding {
+        enabled = true
+    }
 }
 
 dependencies {
@@ -29,6 +32,7 @@ dependencies {
     implementation 'androidx.appcompat:appcompat:1.1.0'
     implementation 'androidx.core:core-ktx:1.1.0'
     implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
+    implementation 'com.github.adriankuta:expandable-recyclerView:0.0.1-beta02'
     testImplementation 'junit:junit:4.12'
     androidTestImplementation 'androidx.test.ext:junit:1.1.1'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

app/src/main/java/com/github/adriankuta/ExpandableAdapter.kt

@@ -0,0 +1,97 @@
+package com.github.adriankuta
+
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import androidx.recyclerview.widget.RecyclerView
+import com.github.adriankuta.databinding.ItemLevel1Binding
+import com.github.adriankuta.databinding.ItemLevel2Binding
+import com.github.adriankuta.databinding.ItemLevel3Binding
+import com.github.adriankuta.expandable_recyclerview.ExpandableTreeNode
+import com.github.adriankuta.expandable_recyclerview.MultilevelRecyclerViewAdapter
+import com.github.adriankuta.expandable_recyclerview.expandableTree
+
+class ExpandableAdapter :
+    MultilevelRecyclerViewAdapter<String, ExpandableAdapter.ExpandableViewHolder>() {
+
+    private var tree: ExpandableTreeNode<String>? = null
+
+    fun setTree(tree: ExpandableTreeNode<String>) {
+        this.tree = tree
+        notifyDataSetChanged()
+    }
+
+    override fun getTreeNodes(): ExpandableTreeNode<String> = tree ?: expandableTree("") {}
+
+    override fun onCreateViewHolder(parent: ViewGroup, nestLevel: Int): ExpandableViewHolder {
+        return when (nestLevel) {
+            1 -> ExpandableViewHolder.Level1(parent.inflateLevel1())
+            2 -> ExpandableViewHolder.Level2(parent.inflateLevel2())
+            3 -> ExpandableViewHolder.Level3(parent.inflateLevel3())
+            else -> throw IllegalArgumentException("Not implemented ViewHolder for nest level: $nestLevel")
+        }
+    }
+
+    override fun onBindViewHolder(
+        holder: ExpandableViewHolder,
+        treeNode: ExpandableTreeNode<String>,
+        nestLevel: Int
+    ) {
+        holder.bind(treeNode) {
+            toggleGroup(it)
+        }
+    }
+
+    sealed class ExpandableViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
+
+        class Level1(private val binding: ItemLevel1Binding) : ExpandableViewHolder(binding.root) {
+            override fun bind(
+                node: ExpandableTreeNode<String>,
+                onClickListener: ((ExpandableTreeNode<String>) -> Unit)?
+            ) {
+                binding.node = node
+                binding.root.setOnClickListener { onClickListener?.invoke(node) }
+            }
+        }
+
+        class Level2(private val binding: ItemLevel2Binding) : ExpandableViewHolder(binding.root) {
+            override fun bind(
+                node: ExpandableTreeNode<String>,
+                onClickListener: ((ExpandableTreeNode<String>) -> Unit)?
+            ) {
+                binding.node = node
+                binding.root.setOnClickListener { onClickListener?.invoke(node) }
+            }
+        }
+
+        class Level3(private val binding: ItemLevel3Binding) : ExpandableViewHolder(binding.root) {
+            override fun bind(
+                node: ExpandableTreeNode<String>,
+                onClickListener: ((ExpandableTreeNode<String>) -> Unit)?
+            ) {
+                binding.node = node
+                binding.root.setOnClickListener { onClickListener?.invoke(node) }
+            }
+        }
+
+
+        abstract fun bind(
+            node: ExpandableTreeNode<String>,
+            onClickListener: ((ExpandableTreeNode<String>) -> Unit)? = null
+        )
+
+    }
+
+    private fun ViewGroup.inflateLevel1(): ItemLevel1Binding {
+        return ItemLevel1Binding.inflate(LayoutInflater.from(context), this, false)
+    }
+
+    private fun ViewGroup.inflateLevel2(): ItemLevel2Binding {
+        return ItemLevel2Binding.inflate(LayoutInflater.from(context), this, false)
+    }
+
+    private fun ViewGroup.inflateLevel3(): ItemLevel3Binding {
+        return ItemLevel3Binding.inflate(LayoutInflater.from(context), this, false)
+    }
+
+}

app/src/main/java/com/github/adriankuta/MainActivity.kt

@@ -1,12 +1,38 @@
 package com.github.adriankuta
 
-import androidx.appcompat.app.AppCompatActivity
 import android.os.Bundle
+import androidx.appcompat.app.AppCompatActivity
+import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
+import com.github.adriankuta.expandable_recyclerview.expandableTree
+import kotlinx.android.synthetic.main.activity_main.*
 
 class MainActivity : AppCompatActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
+
+
+        val tree = expandableTree("World") {
+            child("North America") {
+                child("USA")
+            }
+            child("Europe") {
+                child("Poland") {
+                    child("Warsaw")
+                }
+                child("Germany")
+            }
+            child("Asia") {
+                child("China")
+            }
+        }
+
+        val adapter = ExpandableAdapter()
+        recyclerView.layoutManager = LinearLayoutManager(this, RecyclerView.VERTICAL, false)
+        recyclerView.adapter = adapter
+
+        adapter.setTree(tree)
     }
 }

app/src/main/res/drawable/ic_expand_less_black_24dp.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0">
+    <path
+        android:fillColor="#FF000000"
+        android:pathData="M12,8l-6,6 1.41,1.41L12,10.83l4.59,4.58L18,14z"/>
+</vector>

app/src/main/res/drawable/ic_expand_more_black_24dp.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0">
+    <path
+        android:fillColor="#FF000000"
+        android:pathData="M16.59,8.59L12,13.17 7.41,8.59 6,10l6,6 6,-6z"/>
+</vector>

app/src/main/res/drawable/ic_last_element.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24.0"
+    android:viewportHeight="24.0">
+
+    <path
+        android:pathData="M12,0 l0,13z"
+        android:strokeWidth="2"
+        android:strokeColor="@android:color/black" />
+
+    <path
+        android:pathData="M12.5,12 l12,0"
+        android:strokeWidth="2"
+        android:strokeColor="@android:color/black" />
+
+</vector>

app/src/main/res/drawable/ic_middle_element.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24.0"
+    android:viewportHeight="24.0">
+
+    <path
+        android:pathData="M12,0 l0,24z"
+        android:strokeWidth="2"
+        android:strokeColor="@android:color/black" />
+
+    <path
+        android:pathData="M13,12 l11,0"
+        android:strokeWidth="2"
+        android:strokeColor="@android:color/black" />
+
+</vector>

app/src/main/res/drawable/ic_vertical_line.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24.0"
+    android:viewportHeight="24.0">
+
+    <path
+        android:pathData="M12,0 l0,24"
+        android:strokeWidth="2"
+        android:strokeColor="@android:color/black" />
+
+</vector>

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

@@ -6,13 +6,13 @@
     android:layout_height="match_parent"
     tools:context=".MainActivity">
 
-    <TextView
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:text="Hello World!"
+    <androidx.recyclerview.widget.RecyclerView
+        android:id="@+id/recyclerView"
+        android:layout_width="0dp"
+        android:layout_height="0dp"
         app:layout_constraintBottom_toBottomOf="parent"
-        app:layout_constraintLeft_toLeftOf="parent"
-        app:layout_constraintRight_toRightOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent" />
 
 </androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/layout/item_level_1.xml

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layout>
+
+    <data>
+
+        <variable
+            name="node"
+            type="com.github.adriankuta.expandable_recyclerview.ExpandableTreeNode&lt;String>" />
+
+        <import type="android.view.View" />
+    </data>
+
+    <androidx.constraintlayout.widget.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="wrap_content">
+
+        <ImageView
+            android:id="@+id/expand_icon"
+            android:layout_width="24dp"
+            android:layout_height="0dp"
+            android:scaleType="centerInside"
+            android:src="@{node.expanded ? @drawable/ic_expand_more_black_24dp : @drawable/ic_expand_less_black_24dp}"
+            android:visibility="@{node.children.empty ? View.GONE : View.VISIBLE}"
+            app:layout_constraintBottom_toBottomOf="@id/textView"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="@id/textView"
+            tools:src="@drawable/ic_expand_less_black_24dp" />
+
+        <TextView
+            android:id="@+id/textView"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:padding="8dp"
+            android:text="@{node.value}"
+            app:layout_constraintBottom_toBottomOf="parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toEndOf="@id/expand_icon"
+            app:layout_constraintTop_toTopOf="parent"
+            tools:text="@tools:sample/full_names" />
+    </androidx.constraintlayout.widget.ConstraintLayout>
+</layout>

app/src/main/res/layout/item_level_2.xml

@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layout>
+
+    <data>
+        <variable
+            name="node"
+            type="com.github.adriankuta.expandable_recyclerview.ExpandableTreeNode&lt;String>" />
+
+        <import type="android.view.View" />
+    </data>
+
+    <androidx.constraintlayout.widget.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="wrap_content">
+
+        <ImageView
+            android:id="@+id/expand_icon"
+            android:layout_width="24dp"
+            android:layout_height="0dp"
+            android:layout_marginStart="24dp"
+            android:scaleType="centerInside"
+            android:src="@{node.expanded ? @drawable/ic_expand_more_black_24dp : @drawable/ic_expand_less_black_24dp}"
+            android:visibility="@{node.children.empty ? View.GONE : View.VISIBLE}"
+            app:layout_constraintBottom_toBottomOf="@id/textView"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="@id/textView"
+            tools:src="@drawable/ic_expand_less_black_24dp" />
+
+        <TextView
+            android:id="@+id/textView"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:padding="8dp"
+            android:text="@{node.value}"
+            app:layout_constraintBottom_toBottomOf="parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toEndOf="@id/expand_icon"
+            app:layout_constraintTop_toTopOf="parent"
+            app:layout_goneMarginStart="48dp"
+            tools:text="@tools:sample/full_names" />
+    </androidx.constraintlayout.widget.ConstraintLayout>
+</layout>

app/src/main/res/layout/item_level_3.xml

@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layout>
+
+    <data>
+        <variable
+            name="node"
+            type="com.github.adriankuta.expandable_recyclerview.ExpandableTreeNode&lt;String>" />
+
+        <import type="android.view.View" />
+    </data>
+
+    <androidx.constraintlayout.widget.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="wrap_content">
+
+        <ImageView
+            android:id="@+id/expand_icon"
+            android:layout_width="24dp"
+            android:layout_height="0dp"
+            android:layout_marginStart="48dp"
+            android:scaleType="centerInside"
+            android:src="@{node.expanded ? @drawable/ic_expand_more_black_24dp : @drawable/ic_expand_less_black_24dp}"
+            android:visibility="@{node.children.empty ? View.GONE : View.VISIBLE}"
+            app:layout_constraintBottom_toBottomOf="@id/textView"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="@id/textView"
+            tools:src="@drawable/ic_expand_less_black_24dp" />
+
+        <TextView
+            android:id="@+id/textView"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:padding="8dp"
+            app:layout_goneMarginStart="96dp"
+            android:text="@{node.value}"
+            app:layout_constraintBottom_toBottomOf="parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toEndOf="@id/expand_icon"
+            app:layout_constraintTop_toTopOf="parent"
+            tools:text="@tools:sample/full_names" />
+    </androidx.constraintlayout.widget.ConstraintLayout>
+</layout>

expandable-recyclerview/build.gradle

@@ -15,7 +15,7 @@ android {
         minSdkVersion 23
         targetSdkVersion 29
         versionCode 1
-        versionName "0.0.1-alpha02"
+        versionName "1.0.0"
 
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
         consumerProguardFiles 'consumer-rules.pro'
@@ -35,7 +35,7 @@ dependencies {
     implementation 'androidx.appcompat:appcompat:1.1.0'
     implementation 'androidx.core:core-ktx:1.1.0'
     implementation "androidx.recyclerview:recyclerview:1.1.0"
-    implementation "com.github.adriankuta:tree-structure:1.2.0"
+    implementation "com.github.adriankuta:tree-structure:1.2.3"
 
     testImplementation 'junit:junit:4.12'
     androidTestImplementation 'androidx.test.ext:junit:1.1.1'

expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/ExpandableRecyclerViewAdapter.kt

@@ -3,7 +3,7 @@ package com.github.adriankuta.expandable_recyclerview
 import android.view.ViewGroup
 import androidx.recyclerview.widget.RecyclerView
 
-abstract class MultilevelRecyclerViewAdapter<T, VH : RecyclerView.ViewHolder> :
+abstract class ExpandableRecyclerViewAdapter<T, VH : RecyclerView.ViewHolder> :
     RecyclerView.Adapter<VH>() {
 
     private lateinit var treeNodes: ExpandableTreeNode<T>
@@ -12,25 +12,35 @@ abstract class MultilevelRecyclerViewAdapter<T, VH : RecyclerView.ViewHolder> :
     abstract override fun onCreateViewHolder(parent: ViewGroup, nestLevel: Int): VH
 
     final override fun onBindViewHolder(holder: VH, position: Int) {
-        onBindViewHolder(holder, treeNodes.getVisibleNode(position))
+        val visibleNode = treeNodes.getVisibleNode(position, true)
+        onBindViewHolder(holder, visibleNode, visibleNode.depth())
     }
 
-    abstract fun onBindViewHolder(holder: VH, treeNode: ExpandableTreeNode<T>)
+    abstract fun onBindViewHolder(holder: VH, treeNode: ExpandableTreeNode<T>, nestLevel: Int)
 
     abstract fun getTreeNodes(): ExpandableTreeNode<T>
 
     final override fun getItemCount(): Int {
         treeNodes = getTreeNodes()
-        return treeNodes.getVisibleNodeCount()
+        return treeNodes.getVisibleNodeCount(true) //We don't want to show root element.
     }
 
     final override fun getItemViewType(position: Int): Int {
-
-        return treeNodes.getVisibleNode(position).depth()
+        return treeNodes.getVisibleNode(position, true).depth()
     }
 
     fun toggleGroup(expandableTreeNode: ExpandableTreeNode<T>) {
         expandableTreeNode.expanded = !expandableTreeNode.expanded
         notifyDataSetChanged()
     }
+
+    fun expand(expandableTreeNode: ExpandableTreeNode<T>) {
+        expandableTreeNode.expanded = true
+        notifyDataSetChanged()
+    }
+
+    fun collapse(expandableTreeNode: ExpandableTreeNode<T>) {
+        expandableTreeNode.expanded = false
+        notifyDataSetChanged()
+    }
 }

expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/ExpandableTreeNode.kt

@@ -6,33 +6,78 @@ import com.github.adriankuta.datastructure.tree.TreeNode
 class ExpandableTreeNode<T>(value: T) : TreeNode<T>(value) {
 
     var expanded: Boolean = true
-        set(value) {
-            field = value
-            children.forEach {
-                (it as ExpandableTreeNode).expanded = value
-            }
-        }
 
-    override fun child(value: T, childDeclaration: ChildDeclaration<T>?) {
+    override fun child(value: T, childDeclaration: ChildDeclaration<T>?) : ExpandableTreeNode<T> {
         val newChild = ExpandableTreeNode(value)
         if (childDeclaration != null)
             newChild.childDeclaration()
         addChild(newChild)
+        return newChild
     }
 
-    fun getVisibleNodeCount(): Int {
-        return onlyVisibleItems()
+    /**
+     * @param skipRootNode If `True`, then root node won't be counted.
+     */
+    internal fun getVisibleNodeCount(skipRootNode: Boolean): Int {
+        var size = onlyVisibleItems()
             .size
+
+        if (skipRootNode && size > 0)
+            size--
+
+        return size
     }
 
-    fun getVisibleNode(position: Int): ExpandableTreeNode<T> {
-        return onlyVisibleItems()[position]
+    /**
+     * This function use Pre-order iteration to go through tree:
+     * ```
+     * e.g.
+     *                    1
+     *                  / | \
+     *                 /  |   \
+     *               2    3     4
+     *              / \       / | \
+     *             5    6    7  8  9
+     *            /   / | \
+     *           10  11 12 13
+     *
+     * Output (skipRootNode = false): 1 2 5 10 6 11 12 13 3 4 7 8 9
+     * Output (skipRootNode = true): 2 5 10 6 11 12 13 3 4 7 8 9
+     * ```
+     * @param skipRootNode If `True` root element will be omitted, and position 0 will be for first left child.
+     */
+    internal fun getVisibleNode(position: Int, skipRootNode: Boolean): ExpandableTreeNode<T> {
+        val nodePosition = if (skipRootNode) position + 1 else position
+        return onlyVisibleItems()[nodePosition]
     }
 
-    private fun onlyVisibleItems(): List<ExpandableTreeNode<T>> {
+    /**
+     * @return List of nodes which parent or higher ancestor aren't collapsed.
+     */
+    fun onlyVisibleItems(): List<ExpandableTreeNode<T>> {
         //Visible if parent of node is expanded.
         return map { it as ExpandableTreeNode }
-            .filter { (it.parent as? ExpandableTreeNode)?.expanded ?: true }
+            .filter { allAncestorsAreExpanded(it) }
+    }
+
+    /**
+     * `Ancestor` is a node reachable by repeated proceeding from child to parent.
+     * @return `True` if parent, and all parent's ancestors are expanded.
+     */
+    private fun allAncestorsAreExpanded(node: ExpandableTreeNode<T>): Boolean {
+        var ancestor = node.parent as? ExpandableTreeNode
+        var ancestorsAreExpanded = isAncestorExpanded(ancestor)
+
+        while (ancestorsAreExpanded && ancestor != null) {
+            ancestor = ancestor.parent as? ExpandableTreeNode<T>
+            ancestorsAreExpanded = ancestorsAreExpanded.and(isAncestorExpanded(ancestor))
+        }
+
+        return ancestorsAreExpanded
+    }
+
+    private fun isAncestorExpanded(ancestor: ExpandableTreeNode<T>?): Boolean {
+        return ancestor?.expanded ?: true
     }
 
 }

expandable-recyclerview/src/main/java/com/github/adriankuta/expandable_recyclerview/ExpandableTreeNodeExt.kt

@@ -6,7 +6,7 @@ import com.github.adriankuta.datastructure.tree.ChildDeclaration
 @JvmSynthetic
 inline fun <reified T> expandableTree(
     value: T,
-    childDeclaration: ChildDeclaration<T>
+    childDeclaration: ChildDeclaration<T> = {}
 ): ExpandableTreeNode<T> {
     val treeNode = ExpandableTreeNode(value)
     treeNode.childDeclaration()

expandable-recyclerview/src/test/java/com/github/adriankuta/expandable_recyclerview/ExpandableTreeNodeTest.kt

@@ -0,0 +1,24 @@
+package com.github.adriankuta.expandable_recyclerview
+
+import org.junit.Assert
+import org.junit.Test
+
+class ExpandableTreeNodeTest {
+
+    @Test
+    fun getVisibleNode() {
+        //given
+        val root = expandableTree("Root") {
+            child("Level 1") {
+                child("Level 2") {
+                    child("Level 3") {
+                        child("Level 4")
+                    }
+                }
+            }
+        }
+        root.expanded = false
+
+        Assert.assertEquals("Root", root.onlyVisibleItems().first().value)
+    }
+}