A filterable ListAdapter for RecyclerView

README.md

Filterable List Adapter

These are the steps to use the adapter.

1. Replace the adapter extending ListAdapter with FilterableListAdapter.
2. Implement the method onFilter that provides a List and the string the was passed to the filter method
3. Update the list according the constraint

Usage

val filterAdapter = null // Your adapter instance here
filterAdapter.filter.filter(/*Pass your string here*/)

FilterableListAdapter.kt

abstract class FilterableListAdapter<T, VH : RecyclerView.ViewHolder>(
    diffCallback: DiffUtil.ItemCallback<T>
) : ListAdapter<T, VH>(diffCallback), Filterable {

    private var originalList: List<T> = currentList.toList()

    override fun getFilter(): Filter {
        return object : Filter() {
            override fun performFiltering(constraint: CharSequence?): FilterResults {
                return FilterResults().apply {
                    values = if (constraint.isNullOrEmpty())
                        originalList
                    else
                        onFilter(originalList, constraint.toString())
                }
            }

            @Suppress("UNCHECKED_CAST")
            override fun publishResults(constraint: CharSequence?, results: FilterResults?) {
                submitList(results?.values as? List<T>, true)
            }
        }
    }

    override fun submitList(list: List<T>?) {
        submitList(list, false)
    }

    abstract fun onFilter(list: List<T>, constraint: String): List<T>

    /**
     * This function is responsible for maintaining the
     * actual contents for the list for filtering
     * The submitList for parent class delegates false
     * so that a new contents can be set
     * While a filter pass true which make sure original list
     * is maintained
     *
     * @param filtered True if the list was updated using filter interface
     * */
    private fun submitList(list: List<T>?, filtered: Boolean) {
        if (!filtered)
            originalList = list ?: listOf()

        super.submitList(list)
    }

}