Android - Why Recycler view is not displaying on the device ?? . I think my code is correct but the view is not showing

Question

I just created a simple RecyclerView project which will show 30 basic things . But when i run the file it is not showing anything. In fact my whole source code is just fine.

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/rv_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="10dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:itemCount="12"
        tools:listitem="@layout/recycler_view_item" />

</androidx.constraintlayout.widget.ConstraintLayout> 

MainActivity.kt

package com.saddyahmed.recyclerview

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.constraintlayout.widget.ConstraintLayout
import androidx.recyclerview.widget.LinearLayoutManager
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        rv_main.layoutManager = LinearLayoutManager(this)
        rv_main.adapter = PostAdapter()
    }
}

PostAdapter.kt

package com.saddyahmed.recyclerview

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView


class PostAdapter : RecyclerView.Adapter<PostAdapter.PostViewHolder>() {

    class PostViewHolder(postView: View) : RecyclerView.ViewHolder(postView){

    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): PostViewHolder {
        val postView = LayoutInflater.from(parent.context).inflate(R.layout.recycler_view_item , parent ,false)
        return PostViewHolder(postView)
    }

    override fun onBindViewHolder(holder: PostViewHolder, position: Int) {

    }

    override fun getItemCount(): Int {
        return 30
    }

}

post.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="wrap_content"
    android:padding="5dp"
    android:layout_marginBottom="5dp"
    >

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="50dp"
        android:layout_height="50dp"
        tools:src="@drawable/sunny"
        app:layout_constraintStart_toStartOf="parent"
        android:layout_marginStart="8dp"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="8dp" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:text="Today is Sunny"
        android:textSize="20sp"
        android:textColor="@android:color/black"
        app:layout_constraintTop_toTopOf="@+id/imageView2"
        app:layout_constraintStart_toEndOf="@+id/imageView2"
        android:layout_marginStart="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toTopOf="@+id/textView2" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="285dp"
        android:layout_height="20dp"
        tools:text="Today is sunny day lets go there"
        app:layout_constraintBottom_toBottomOf="@+id/imageView2"
        app:layout_constraintStart_toEndOf="@+id/imageView2"
        android:layout_marginStart="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginEnd="8dp"
        app:layout_constraintHorizontal_bias="0.050" />

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:text="Actions"
        app:layout_constraintTop_toTopOf="@+id/imageView2"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginEnd="8dp" />
</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

First, add a constructor to your PostAdapter that accepts data and get your data into your PostAdapter, for example:

myDataList = ...; // Get data from somewhere
rv_main = PostAdapter(myDataList);

Then bind it in your onBindViewHolder:

override fun onBindViewHolder(holder: PostViewHolder, position: Int) {
   holder.bindData(myDataList.get(position));
}

Also getItemCount() should return myDataList.size()