Merge pull request #2 from AdrianKuta/sample

Update README.md

README.md

@@ -4,11 +4,100 @@
 [![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)
 
-<img src="https://github.com/AdrianKuta/Expandable-RecyclerView/blob/master/Demo.gif" width="300" />
+With this adapter you can add expand feature to regular RecyclerView.
+All objects are store in [Tree (Data structure)](https://github.com/AdrianKuta/Tree-Data-Structure), so adapter can create multilevel expandable groups.
+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" />
 
-This RecyclerViewAdapter use Tree(Data Structure) to keep all objects.
 ## 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! ;-)