Kotlin : Recyclerview on Fragment ,how to make the default total price is the first item multiply 1 - kotlin

Question

I got stuck in the situation ..
The idea is ,make the display total price with the first item selected multiply the first value of popup menu which is 1 ,I was trying to make the first item as the initial price ,but the total price became the first item price * selected value of popup menu ....
I have no idea what happend ..
Could you please help me check my code ,thank you so much in advance :
Product.kt
package com.gearsrun.recyclerviewfragmentapplication
data class Product(var price : String)
ProductAdapter.kt
package com.gearsrun.recyclerviewfragmentapplication
import android.graphics.Color
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import kotlinx.android.synthetic.main.item_layout.view.*
class ProductAdapter(private val productList:List<Product>): RecyclerView.Adapter<ProductAdapter.ProductViewHolder>() {
private var selectedItemPosition :Int = 0
private var mlistener : onItemClickListener ?=null
fun interface onItemClickListener{
fun onItemClick(position: Int)
}
fun setOnItemClickListener(listener: onItemClickListener){
mlistener = listener
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
val itemView = LayoutInflater.from(parent.context).inflate(R.layout.item_layout,parent,false)
return ProductViewHolder(itemView,mlistener)
}
override fun onBindViewHolder(holder: ProductAdapter.ProductViewHolder, position: Int) {
val currentItem = productList[position]
holder.price.text = currentItem.price
holder.itemView.setOnClickListener {
selectedItemPosition = position
notifyDataSetChanged()
}
if(selectedItemPosition == position){
holder.itemView.cardView.setBackgroundColor(Color.parseColor("#FAFAD2"))
}else{
holder.itemView.cardView.setBackgroundColor(Color.parseColor("#FFFFFF"))
}
}
override fun getItemCount() = productList.size
class ProductViewHolder(itemView: View,listener: onItemClickListener):RecyclerView.ViewHolder(itemView) {
val price : TextView = itemView.price
init {
itemView.setOnClickListener {
listener?.onItemClick(absoluteAdapterPosition)
}
}
}
}
fragment_home.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".fragment.HomeFragment">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical">
<!--Recycler View-->
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/giftRecycleView"
android:layout_width="match_parent"
android:layout_height="180dp"
android:layout_marginTop="30dp"
/>
<!--Selected option will display here-->
<LinearLayout
android:layout_width="match_parent"
android:gravity="center"
android:padding="16dp"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Select amount : "
android:textColor="#color/black"
android:textSize="18sp"/>
<TextView
android:id="#+id/selectedTv"
android:layout_width="100dp"
android:layout_height="60dp"
android:textStyle="bold"
android:gravity="center"
android:layout_marginLeft="10dp"
android:background="#color/black"
android:textColor="#color/white"
android:textSize="20sp"
android:text="1" />
</LinearLayout>
<!--Total price-->
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:padding="10dp"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Total : "
android:textColor="#color/black"
android:textSize="18sp"/>
<TextView
android:id="#+id/price_t"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="#color/black"
android:textSize="18sp"/>
</LinearLayout>
</LinearLayout>
</FrameLayout>
HomeFragment.kt
package com.gearsrun.recyclerviewfragmentapplication.fragment
import android.os.Bundle
import android.util.Log
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.Menu
import android.view.View
import android.view.ViewGroup
import android.widget.PopupMenu
import android.widget.Toast
import androidx.recyclerview.widget.LinearLayoutManager
import com.gearsrun.recyclerviewfragmentapplication.Product
import com.gearsrun.recyclerviewfragmentapplication.ProductAdapter
import com.gearsrun.recyclerviewfragmentapplication.R
import kotlinx.android.synthetic.main.fragment_home.*
import kotlin.properties.Delegates
class HomeFragment : Fragment(R.layout.fragment_home) {
//recyclerview
private val productList = generateProduct()
private var select_price = 0 // gift price
private var select_num = 1 //popup menu value
private fun refreshOutput(){
price_t.text = (select_num*select_price).toString()
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val adapter = ProductAdapter(productList)
giftRecycleView.adapter = adapter
adapter.setOnItemClickListener{position : Int->
select_price = productList[position].price.toInt()
refreshOutput()
}
giftRecycleView.layoutManager = LinearLayoutManager(context,LinearLayoutManager.HORIZONTAL,false)
//popup menu
val popupMenu = PopupMenu(
context,
selectedTv
)
for(i in 0..5){
popupMenu.menu.add(Menu.NONE,i,i,i.toString())
}
//handle menu clicks
popupMenu.setOnMenuItemClickListener { menuItem ->
val i = menuItem.itemId+1
selectedTv.text = i.toString()
select_num = i
refreshOutput()
true
}
//handle menu click to show menu
selectedTv.setOnClickListener {
popupMenu.show()
}
//calculate the total price
refreshOutput()
}
private fun generateProduct(): List<Product>{
val list = ArrayList<Product>()
list.add(Product("5"))
list.add(Product("6"))
list.add(Product("7"))
return list
}
}

Answer 1

If I understood correctly the popup has a value other than textView and this value is used for the calculation. And the problem comes before selecting amout.
You can set a default popup value like here
How to set a default selected option in Android popup menu?

Answer 2

First I have to say something about this piece of code. If you find yourself copy-pasting code like this, you need to step back and simplify it. Your setup of the popup menu could be cut down to this:
//add menu items to popup menu
for (i in 0..4) {
popupMenu.menu.add(Menu.NONE, i, i, (i + 1).toString())
}
//handle menu clicks
popupMenu.setOnMenuItemClickListener { menuItem ->
val i = menuItem.itemId + 1
selectedTv.text = i.toString()
select_num = i
total_price = select_num * select_price
price_t.text = total_price.toString()
true
}
And here you can see the problem. You are only updating the calculated value when the popup menu is clicked, but not when a different view is selected in the adapter. You should create a function that updates the calculation and puts it in the text view, and call them from both listeners (adapter's item click listener and the popup menu listener).
It's kind of weird to do this with local variables and more unusual to define a function inside onViewCreated(). You should promote them to private properties so the function goes outside onViewCreated(). Eliminate the total_price variable because you never use it in a useful way. It will always be out of date once something else changes, so it is not helping you at all. So your code will end up looking like:
private var select_price = 0
private var select_num = 1
private fun refreshOutput() {
price_t.text = (select_num * select_price).toString()
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val adapter = ProductAdapter(productList)
giftRecycleView.adapter = adapter
adapter.setOnItemClickListener(object :ProductAdapter.onItemClickListener{
override fun onItemClick(position: Int) {
select_price = productList[position].price.toInt()
refreshOutput()
}
})
giftRecycleView.layoutManager = LinearLayoutManager(context,LinearLayoutManager.HORIZONTAL,false)
//popup menu
val popupMenu = PopupMenu(
context,
selectedTv
)
for (i in 0..5) {
popupMenu.menu.add(Menu.NONE, i, i, i.toString())
}
//handle menu clicks
popupMenu.setOnMenuItemClickListener { menuItem ->
val i = menuItem.itemId + 1
selectedTv.text = i.toString()
select_num = i
refreshOutput()
true
}
//handle menu click to show menu
selectedTv.setOnClickListener {
popupMenu.show()
}
//calculate the total price
refreshOutput() // show initial value
}
And a couple of tips about Kotlin. You are misusing lateinit for your listener. lateinit is for properties that are guaranteed to be initialized before they are accessed anywhere else in your code. This is mostly only applicable for classes that are instantiated by reflection, and the subclass's code's first entry point is somewhere other than the constructor, like in an Activity's onCreate() or Fragment's onCreateView()/onViewCreated(). This is not true for your Adapter, so by marking the property lateinit, you are only using the keyword to subvert null-safety. The property should simply be nullable, and a null-safe call should be used with it in the one place where you actually use it.
Also, if you define your interface as a fun interface, you can take advantage of lambda syntax.
private var mlistener : onItemClickListener? = null
fun interface onItemClickListener{
fun onItemClick(position: Int)
}
fun setOnItemClickListener(listener: onItemClickListener){
mlistener = listener
}
//...
// In product view holder:
init {
itemView.setOnClickListener {
listener?.onItemClick(absoluteAdapterPosition)
}
}
// In Fragment:
adapter.setOnItemClickListener { position: Int ->
select_price = productList[position].price.toInt()
refreshOutput()
}
And finally, my answer is just explaining how to get your current code working. Really, you should convert the select_price and select_num into LiveDatas or StateFlows in a ViewModel. Then you would use these values to set up the state of your UI elements, and they will persist correctly if the screen is rotated. The way it is now, when the screen rotates, your currently selected price and number will be lost.