Multilevel Expandable RecyclerView

With this adapter you can add expand feature to regular RecyclerView.

All objects are store in 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.

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.

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:

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:

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:

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! ;-)