MainActivity is as follows. Nothing comes out on the screen, but I don't know which part is wrong. How can I add the value of TV_item_name?
And in the log, it's from the DetailViewAdapter of the inner class. Log.d (logTag,onCreateViewHolder11iscaled") value is also not output, so what is the problem?
package com.example.test_recyclerview
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.cardview.widget.CardView
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.test_recyclerview.databinding.ActivityMainBinding
class MainActivity : AppCompatActivity() {
private lateinit var binding : ActivityMainBinding
var logTag : String? = "로그 MainActivity"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
val view = binding.root
setContentView(view)
Log.d(logTag,"111 onCreate is called")
binding.mRecyclerView.layoutManager = LinearLayoutManager(this)
val adapter = DetailViewAdapter()
Log.d(logTag,"222 onCreate is called")
binding.mRecyclerView.adapter = adapter
}
override fun onDestroy() {
super.onDestroy()
binding.mRecyclerView.adapter = null
}
inner class DetailViewAdapter : RecyclerView.Adapter<DetailViewAdapter.ViewHolder>() {
private var list = ArrayList<String>()
var logTag : String? = "로그 MainActivity"
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): DetailViewAdapter.ViewHolder {
Log.d(logTag,"onCreateViewHolder11 is called")
list = getItemList()
val view = LayoutInflater.from(parent.context).inflate(R.layout.item_custom_row, parent, false)
return ViewHolder(view)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
Log.d(logTag,"onBindViewHolder is called")
for (i in 1 until list.size) {
Log.d(logTag,"onBindViewHolder is called // list[$i] =" list[i])
holder.tvItem.text = list[i]
}
}
override fun getItemCount(): Int {
return list.size
}
private fun getItemList(): ArrayList<String> {
for (i in 1..8) {
list.add(i, "Item $i")
}
return list
}
inner class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
val tvItem : TextView = view.findViewById(R.id.tv_item_name)
val cardViewItem : CardView = view.findViewById(R.id.card_view_item)
}
}
}
item_custom_row.xml
<?xml version="1.0" encoding="utf-8"?>
`enter code here`<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<androidx.cardview.widget.CardView
android:id="@ id/card_view_item"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:padding="10dp"
app:cardCornerRadius="5dp"
app:cardElevation="3dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal"
tools:ignore="UseCompoundDrawables">
<ImageView
android:layout_width="50dp"
android:layout_height="50dp"
android:contentDescription="@string/app_name"
android:src="@mipmap/ic_launcher" />
<TextView
android:id="@ id/tv_item_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:textColor="@android:color/black"
android:textSize="18sp"
android:textStyle="bold"
tools:text="Item" />
</LinearLayout>
</androidx.cardview.widget.CardView>
</LinearLayout>
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="@ id/m_RecyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
CodePudding user response：
From the code you posted I can see two problems with your code.
First one is that you are trying to populate the list of data from inside the view holder. What happens is the following:
- The adapter is created
- The adapter wants to know how many viewholders it should create to see how to populate the recycler view.
- The adapter calls getItemCount and this method returns 0, since the list hasen't been populated.
- Nothing else is called since nothing else has to be executed.
So, to fix this, the easiest way would be to make getItemCount return 8 and you are set. But, a better way to fix this is to instaintiate your list outside of your adapter, in your activity for example, and pass it as a constructor parameter when you initialize your adapter.
The second problem I'm seeing is on the method onBindViewHolder. You are iterating trough the list to set the text and this will cause that for all items you will only set the text as in the last item (item 8). You need to remember that onBindViewHolder is a method that is called when a view holder needs to refresh it contents because it is going to be used to display a different item of the list, that's why this method is passed the position as parameter, so you can do something like:
holder.tvItem.text = list[position]
** As a side note for the second issue, a more general approach I have seen and used to render the contents of the view holder, is to create a public method called "bind" which is passed the item that needs to be rendered and on the view holder you will have the logic on how to paint it. Something like:
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.bind(list[position])
}
/// Inside the view holder
fun bind(item: String) {
tvItem.text = item
}
CodePudding user response：
The issue is you're assigning list in onCreateViewHolder but it won't be called since your list.size is returning 0.
Rightly pointed out in this answer
- Create list outside adapter & pass it from constructor
- Change implementation in
onBindViewHolder
Following is the complete example for your use case:
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding
var logTag: String? = "로그 MainActivity"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
val view = binding.root
setContentView(view)
Log.d(logTag, "111 onCreate is called")
binding.mRecyclerView.layoutManager = LinearLayoutManager(this)
val adapter = DetailViewAdapter(getItemList())
Log.d(logTag, "222 onCreate is called")
binding.mRecyclerView.adapter = adapter
}
private fun getItemList(): ArrayList<String> {
val list = ArrayList<String>()
for (i in 1..8) {
list.add("Item $i")
}
return list
}
override fun onDestroy() {
super.onDestroy()
binding.mRecyclerView.adapter = null
}
inner class DetailViewAdapter(private val list: ArrayList<String>) :
RecyclerView.Adapter<DetailViewAdapter.ViewHolder>() {
var logTag: String? = "로그 MainActivity"
override fun onCreateViewHolder(
parent: ViewGroup,
viewType: Int
): DetailViewAdapter.ViewHolder {
Log.d(logTag, "onCreateViewHolder11 is called")
val view =
LayoutInflater.from(parent.context).inflate(R.layout.item_custom_row, parent, false)
return ViewHolder(view)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
Log.d(logTag, "onBindViewHolder is called")
holder.tvItem.text = list[position]
}
override fun getItemCount(): Int {
return list.size
}
inner class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
val tvItem: TextView = view.findViewById(R.id.tv_item_name)
val cardViewItem: CardView = view.findViewById(R.id.card_view_item)
}
}
}