How to use select / deselect all items in Recyclerview Android

In my application I have one fragment and in this fragment I have one recyclerview and 2 button.
Button 1 is Select all and button 2 is Deselect all.

I write below codes for recyclerview:

`

private lateinit var binding: ItemDayMyBinding

private lateinit var context: Context

private val TYPE_HEADER = 0
private val TYPE_DAY = 1
private var firstDayDayOfWeek = 0
private var totalDays = 0
private var todayPosition = -1

private val addedDateList = mutableListOf<PersianDate>()
private val removedDateList = mutableListOf<PersianDate>()

private val selectedDays = mutableListOf<DayEntity>()

init {
    firstDayDayOfWeek = items[0].dayOfWeek
    totalDays = items.size
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
    binding = ItemDayMyBinding.inflate(LayoutInflater.from(parent.context), parent, false)
    context = parent.context
    return ViewHolder()
}

override fun getItemCount() = 7 * 7

override fun getItemViewType(position: Int): Int {
    return if (isPositionHeader(position)) {
        TYPE_HEADER
    } else {
        TYPE_DAY
    }
}

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    holder.bind(position)
    holder.setIsRecyclable(false)
}

inner class ViewHolder : RecyclerView.ViewHolder(binding.root) {
    //Bind data
    fun bind(pos: Int) {
        binding.apply {
            var position = pos
            position += 6 - (position % 7) * 2
            //Check
            if (totalDays < position - 6 - firstDayDayOfWeek) {
                return
            } else {
                //Day
                if (!isPositionHeader(position)) {
                    if (position - 7 - firstDayDayOfWeek >= 0) {
                        val day = items[position - 7 - firstDayDayOfWeek]

                        dayTxt.isVisible = true
                        //Day text options
                        dayTxt.text = day.num
                        dayTxt.setTextColor(ContextCompat.getColor(context, R.color.black))
                        //Holiday
                        if (day.isHoliday) {
                            dayTxt.setTextColor(ContextCompat.getColor(context, R.color.mystic))
                        } else {
                            dayTxt.setTextColor(ContextCompat.getColor(context, R.color.black))
                            //Today
                            if (day.isToday) {
                                todayPosition = position
                            }
                            //Previous of today
                            if (position < todayPosition) {
                                dayTxt.setTextColor(ContextCompat.getColor(context, R.color.spanishGray))
                            } else {
                                dayTxt.setTextColor(ContextCompat.getColor(context, R.color.black))
                            }
                        }
                    } else {
                        dayTxt.isVisible = false
                    }
                } else {
                    //Header
                    dayTxt.text = NAME_OF_DAYS_OF_WEEK_NAME[position]
                    dayTxt.setTextColor(ContextCompat.getColor(context, R.color.weldonBlue))
                }
            }
        }
    }
}

private fun isPositionHeader(position: Int) = position < 7

I want when click on select all button, select all today and next days.
Not previous days!

Searched in stackoverflow and find this:

`

ArrayList<Item> selected = new ArrayList<Item>();
ArrayList<Item> items = new ArrayList<Item>();

public void selecteAll() {
    selected.clear();
    selected.addAll(items);
    notifyDataSetChanged();
}

public void clearAll() {
    selected.clear();
    notifyDataSetChanged();
}

public void bindView() {
    Item item = items.get(position);

    if(selected.contains(item) {
        // Do selected action
    } else {
       // Non selecetd ctions
    }
}

`

In this solution just select all of items, but I want just select today and next days!

How can I it?

>Solution :

Not getting exactly what you have in Item and other data but yes below code can give you hint what you can do

I want when click on select all button, select all today and next days. 

As per your requirement , you first need to determine that you need to perform selection operation or not and from where

So first you declare one boolean in your adapter class

private boolean needToSelectDays = false

after declaring it in adapter , you can make change in selectAll function like this

public void selecteAll() {
    needToSelectDays = true
    notifyDataSetChanged();
}

public void clearAll() {
    needToSelectDays = false
    notifyDataSetChanged();
}

in above code we are managing boolean variable only .. now it is time of use it and as per your code , you are binding data in ViewHolder class so you can add this code within your existing code

fun bind(pos: Int) {
   // your existing code
   if(needToSelectDays && dayGettingFromItem >= currentDay){
      // you can write here logic of selecting date
   }else{
     // you can write here logic of unselecting dat
   }
}

hope it will help you