Error inflating android.support.v7.widget.CardView

Question

Before diving into the code, I do want to mention that Android Studio says The following class couldn't be found: android.support.v7.widget.CardView, even though I have it downloaded it.(Images below)

(Error saying CardView not found, though no download option is found.)

Here's the code for the activity having the error.

ContactsActivity.kt

(contactView is the RecyclerView)

package com.smartherd.msgshareapp

import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.smartherd.msgshareapp.models.Contact
import com.smartherd.msgshareapp.models.adapters.ContactAdapter
import kotlinx.android.synthetic.main.activity_contacts.*

class ContactsActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val layoutManager = LinearLayoutManager(this)
        layoutManager.orientation = LinearLayoutManager.VERTICAL

        contactsView.layoutManager = layoutManager  // Oops! contactsView is NULL!

        contactsView.adapter = ContactAdapter(this, Contact.allContacts)
    }
}

Here's activity_contact.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:baselineAligned="false"
    android:orientation="vertical"
    android:padding="10dp">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/contactsView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="vertical" />
</LinearLayout>

Contact class

package com.smartherd.msgshareapp.models

import org.json.JSONArray
import org.json.JSONObject
import java.io.File

data class Contact(val name: String, val phone: String, val email: String) {
    companion object {

       val allContacts: List<Contact>
        get() {
            val json = JSONObject(File("contacts.json").readText()).getJSONArray("contacts")
            // Looks like {"contacts": [{"name": ..., "email": ..., "phone": ...}, ...]}

            val contacts = mutableListOf<Contact>()

            var i = 0

            while (i < json.length()) {
                val name = json.getJSONObject(i).getString("name")
                val phone = json.getJSONObject(i).getString("phone")
                val email = json.getJSONObject(i).getString("email")

                contacts.add(Contact(name, phone, email))

                ++i
            }

            return contacts
        }

    }
}

And the Contact Adapter class (ContactAdapter.kt)

package com.smartherd.msgshareapp.models.adapters

import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.smartherd.msgshareapp.R
import com.smartherd.msgshareapp.models.Contact
import kotlinx.android.synthetic.main.card_contact.view.*

class ContactAdapter(val context: Context, val contacts: List<Contact>) :
    RecyclerView.Adapter<ContactAdapter.ContactHolder>() {

    inner class ContactHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        fun initialize(contact: Contact) {
            itemView.contactName.text = "${contact.name}\n${contact.email}"
            // itemView.contactImage is not set yet.
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ContactHolder =
        ContactHolder(
            LayoutInflater.from(context).inflate(R.layout.card_contact, parent, false)
        )

    override fun getItemCount(): Int = contacts.size

    override fun onBindViewHolder(holder: ContactHolder, position: Int) = holder.initialize(contacts[position])
}

Answer 1

At first add setContentView();

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main) //missing
    val recyclerView = findViewById(R.id.contactsView) as RecyclerView

Use Exact version App Level build.gradle

 dependencies {

       implementation 'com.android.support:cardview-v7:28.0.0'
       implementation 'com.android.support:recyclerview-v7:28.0.0'
      }

FYI

You are using very old versions. If you want to use latest then libraries will not work unless you make the following changes in your app:

• Upgrade compileSdkVersion to 28 or later.
• Update your app to use Jetpack (AndroidX).

AndroidX replaces the original support library APIs with packages in the androidx namespace. Read official guideline about AndroidX Overview.

Your Cardview & recyclerview will

 implementation 'androidx.cardview:cardview:1.0.0'
 implementation 'androidx.recyclerview:recyclerview:1.1.0'