Simple Android RecyclerView example

Question

I\'ve made a list of items a few times using Android\'s RecyclerView, but it is a rather complicated process. Going through one of the numerous tutorials online

Answer 1

You can use abstract adapter with diff utils and filter

SimpleAbstractAdapter.kt

abstract class SimpleAbstractAdapter(private var items: ArrayList = arrayListOf()) : RecyclerView.Adapter() {
   protected var listener: OnViewHolderListener? = null
   private val filter = ArrayFilter()
   private val lock = Any()
   protected abstract fun getLayout(): Int
   protected abstract fun bindView(item: T, viewHolder: VH)
   protected abstract fun getDiffCallback(): DiffCallback?
   private var onFilterObjectCallback: OnFilterObjectCallback? = null
   private var constraint: CharSequence? = ""

override fun onBindViewHolder(vh: VH, position: Int) {
    getItem(position)?.let { bindView(it, vh) }
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH {
    return VH(parent, getLayout())
}

override fun getItemCount(): Int = items.size

protected abstract class DiffCallback : DiffUtil.Callback() {
    private val mOldItems = ArrayList()
    private val mNewItems = ArrayList()

    fun setItems(oldItems: List, newItems: List) {
        mOldItems.clear()
        mOldItems.addAll(oldItems)
        mNewItems.clear()
        mNewItems.addAll(newItems)
    }

    override fun getOldListSize(): Int {
        return mOldItems.size
    }

    override fun getNewListSize(): Int {
        return mNewItems.size
    }

    override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
        return areItemsTheSame(
                mOldItems[oldItemPosition],
                mNewItems[newItemPosition]
        )
    }

    abstract fun areItemsTheSame(oldItem: T, newItem: T): Boolean

    override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
        return areContentsTheSame(
                mOldItems[oldItemPosition],
                mNewItems[newItemPosition]
        )
    }

    abstract fun areContentsTheSame(oldItem: T, newItem: T): Boolean
}

class VH(parent: ViewGroup, @LayoutRes layout: Int) : RecyclerView.ViewHolder(LayoutInflater.from(parent.context).inflate(layout, parent, false))

interface OnViewHolderListener {
    fun onItemClick(position: Int, item: T)
}

fun getItem(position: Int): T? {
    return items.getOrNull(position)
}

fun getItems(): ArrayList {
    return items
}

fun setViewHolderListener(listener: OnViewHolderListener) {
    this.listener = listener
}

fun addAll(list: List) {
    val diffCallback = getDiffCallback()
    when {
        diffCallback != null && !items.isEmpty() -> {
            diffCallback.setItems(items, list)
            val diffResult = DiffUtil.calculateDiff(diffCallback)
            items.clear()
            items.addAll(list)
            diffResult.dispatchUpdatesTo(this)
        }
        diffCallback == null && !items.isEmpty() -> {
            items.clear()
            items.addAll(list)
            notifyDataSetChanged()
        }
        else -> {
            items.addAll(list)
            notifyDataSetChanged()
        }
    }
}

fun add(item: T) {
    items.add(item)
    notifyDataSetChanged()
}

fun add(position:Int, item: T) {
    items.add(position,item)
    notifyItemInserted(position)
}

fun remove(position: Int) {
    items.removeAt(position)
    notifyItemRemoved(position)
}

fun remove(item: T) {
    items.remove(item)
    notifyDataSetChanged()
}

fun clear(notify: Boolean=false) {
    items.clear()
    if (notify) {
        notifyDataSetChanged()
    }
}

fun setFilter(filter: SimpleAdapterFilter): ArrayFilter {
    return this.filter.setFilter(filter)
}

interface SimpleAdapterFilter {
    fun onFilterItem(contains: CharSequence, item: T): Boolean
}

fun convertResultToString(resultValue: Any): CharSequence {
    return filter.convertResultToString(resultValue)
}

fun filter(constraint: CharSequence) {
    this.constraint = constraint
    filter.filter(constraint)
}

fun filter(constraint: CharSequence, listener: Filter.FilterListener) {
    this.constraint = constraint
    filter.filter(constraint, listener)
}

fun getFilter(): Filter {
    return filter
}

interface OnFilterObjectCallback {
    fun handle(countFilterObject: Int)
}

fun setOnFilterObjectCallback(objectCallback: OnFilterObjectCallback) {
    onFilterObjectCallback = objectCallback
}

inner class ArrayFilter : Filter() {
    private var original: ArrayList = arrayListOf()
    private var filter: SimpleAdapterFilter = DefaultFilter()
    private var list: ArrayList = arrayListOf()
    private var values: ArrayList = arrayListOf()


    fun setFilter(filter: SimpleAdapterFilter): ArrayFilter {
        original = items
        this.filter = filter
        return this
    }

    override fun performFiltering(constraint: CharSequence?): Filter.FilterResults {
        val results = Filter.FilterResults()
        if (constraint == null || constraint.isBlank()) {
            synchronized(lock) {
                list = original
            }
            results.values = list
            results.count = list.size
        } else {
            synchronized(lock) {
                values = original
            }
            val result = ArrayList()
            for (value in values) {
                if (constraint!=null && constraint.trim().isNotEmpty() && value != null) {
                    if (filter.onFilterItem(constraint, value)) {
                        result.add(value)
                    }
                } else {
                    value?.let { result.add(it) }
                }
            }
            results.values = result
            results.count = result.size
        }
        return results
    }

    override fun publishResults(constraint: CharSequence, results: Filter.FilterResults) {
        items = results.values as? ArrayList ?: arrayListOf()
        notifyDataSetChanged()
        onFilterObjectCallback?.handle(results.count)
    }

}

class DefaultFilter : SimpleAdapterFilter {
    override fun onFilterItem(contains: CharSequence, item: T): Boolean {
        val valueText = item.toString().toLowerCase()
        if (valueText.startsWith(contains.toString())) {
            return true
        } else {
            val words = valueText.split(" ".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
            for (word in words) {
                if (word.contains(contains)) {
                    return true
                }
            }
        }
        return false
    }
  }
}

And extend abstract adapter with implements methods

TasksAdapter.kt

import android.annotation.SuppressLint
  import kotlinx.android.synthetic.main.task_item_layout.view.*

class TasksAdapter(private val listener:TasksListener? = null) : SimpleAbstractAdapter() {
override fun getLayout(): Int {
    return R.layout.task_item_layout
}

override fun getDiffCallback(): DiffCallback? {
    return object : DiffCallback() {
        override fun areItemsTheSame(oldItem: Task, newItem: Task): Boolean {
            return oldItem.id == newItem.id
        }

        override fun areContentsTheSame(oldItem: Task, newItem: Task): Boolean {
            return oldItem.items == newItem.items
        }
    }
}

@SuppressLint("SetTextI18n")
override fun bindView(item: Task, viewHolder: VH) {
    viewHolder.itemView.apply {
        val position = viewHolder.adapterPosition
        val customer = item.customer
        val customerName = if (customer != null) customer.name else ""
        tvTaskCommentTitle.text = customerName + ", #" + item.id
        tvCommentContent.text = item.taskAddress
        ivCall.setOnClickListener {
            listener?.onCallClick(position, item)
        }
        setOnClickListener {
            listener?.onItemClick(position, item)
        }
    }
}

 interface TasksListener : SimpleAbstractAdapter.OnViewHolderListener {
    fun onCallClick(position: Int, item: Task)
 }
}

Init adapter

mAdapter = TasksAdapter(object : TasksAdapter.TasksListener {
            override fun onCallClick(position: Int, item:Task) {
            }

            override fun onItemClick(position: Int, item:Task) {

            }
        })
rvTasks.adapter = mAdapter

and fill

mAdapter?.addAll(tasks)

add custom filter

mAdapter?.setFilter(object : SimpleAbstractAdapter.SimpleAdapterFilter {
            override fun onFilterItem(contains: CharSequence, item:Task): Boolean {
                return contains.toString().toLowerCase().contains(item.id?.toLowerCase().toString())
            }
    })

filter data

mAdapter?.filter("test")