With AccordionRecycler you can easily create awesome RecyclerViews, containing infinitely nested items and the ability to expand or collapse any part of the View at will.

Programming language: Kotlin
License: Apache License 2.0
Latest version: v0.5

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License Android Arsenal Bintray

Android RecyclerView Adapter with nested items & expand/contract functionality

With AccordionRecycler you can easily create awesome RecyclerViews, containing infinitely nested items and the ability to expand or collapse any part of the View at will.


implementation 'com.izikode.izilib:accordionrecycler:0.5'


Have your Model Classes implement the AccordionRecyclerData interface.

  • The Adapter needs a way to get the ViewType, Primary data and the Enclosed (child) data, if existing. You use the above interface to provide those.
  • Fill the diamond operator with the type the model provides.
  • Optionally, you can use a base class as a reference for your different data sub-classes and also your ViewHolders. In the provided demo, and examples below, ColorData is the base class and it provided itself. ```kotlin abstract class ColorData : AccordionRecyclerData

data class RedData(

    var arrayOfPink: Array<PinkData> = arrayOf()

) : ColorData(RedViewHolder.VIEW_TYPE) {

override val mainData: ColorData?
        get() = this

override val enclosedDataArray: Array<out AccordionRecyclerData<out ColorData?>>?
        get() = arrayOfPink


data class GrayData( ... ) : ColorData() { ... } data class PinkData( ... ) : ColorData() { ... } data class WhiteData( ... ) : ColorData() { ... }

#### Have your ViewHolders extend the ```AccordionRecyclerViewHolder``` abstract class.
- Provide the ViewHolder constructor with the parent ViewGroup and the layout to be inflated.
- Fill the diamond operator with the type of Model being handled.
- Again, optionally, create a base ViewHolder as a reference.
abstract class ColorViewHolder<Data>( ... ) : AccordionRecyclerViewHolder<Data> where Data : ColorData

class RedViewHolder(parent: ViewGroup) : ColorViewHolder<RedData>(parent, R.layout.view_holder_red) {

    override var data: RedData? = null

    companion object {
        const val VIEW_TYPE = 2


class GrayViewHolder( ... ) : ColorViewHolder<GrayData>
class PinkViewHolder( ... ) : ColorViewHolder<GrayData>
class WhiteViewHolder( ... ) : ColorViewHolder<RedData>

Create an Adapter that extends the AccordionRecyclerAdapter abstract class.

  • Override the buildViewHolder function to provide new ViewHolder instances.
  • Override the updateViewHolder function to update each item being recycled. The AccordionRecyclerItemDetails parameter contains information about the current item and all enclosing (parent) items, when existing. This allows for unlimited visual combinations for all view types.
  • Expand/Collapse is accomplished with:
    • removeItem to remove an item and all it's child items, if existing.
    • removeEnclosedItems to remove the child items only.
    • addItems to add all items and their child items, if existing.
    • addEnclosedItems to add all items as child items to another.
  • Optionally, you can modify how each item is handled when it is iterated and added into the recycler data. You do that by overriding the processForAdditionalItems function. You can use this feature to handle edge case. One such case is shown in the demo, in which whenever a Pink item does not have any child White items, a new item is added, showing the text 'Nothing to see here'.

    class MainAccordionAdapter : AccordionRecyclerAdapter<ColorViewHolder<out ColorData>, ColorData>() {
    override fun buildViewHolder(parent: ViewGroup, viewType: Int): ColorViewHolder<out ColorData> =
            when(viewType) {
                RedViewHolder.VIEW_TYPE -> RedViewHolder(parent)
                PinkViewHolder.VIEW_TYPE -> PinkViewHolder(parent)
                WhiteViewHolder.VIEW_TYPE -> WhiteViewHolder(parent)
                else -> GrayViewHolder(parent)
    override fun updateViewHolder(position: Int, viewHolder: ColorViewHolder<out ColorData>, data: ColorData?, 
                details: AccordionRecyclerItemDetails) {
            when (viewHolder) {
                is RedViewHolder -> viewHolder.apply { ... }
                is PinkViewHolder -> viewHolder.apply { ... }
                is WhiteViewHolder -> viewHolder.apply { ... }
                else -> (viewHolder as GrayViewHolder).apply { ... }
    override fun processForAdditionalItems(position: Int, item: AccordionRecyclerData<out ColorData?>?)
            : Array<out AccordionRecyclerData<out ColorData?>?> = item?.let {
                    if (it is PinkData && it.enclosedDataArray.isNullOrEmpty()) {
                    } else {
                        super.processForAdditionalItems(position, item)
                } ?: super.processForAdditionalItems(position, item)


#### For a full example, see the sample app.

## Licence

Copyright 2018 Fanis Veizis

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

*Note that all licence references and agreements mentioned in the AccordionRecycler README section above are relevant to that project's source code only.