Data Class Example Using Kotlin

Data classes are a powerful kind of classes which avoid the boilerplate we need in Java to create POJO: classes which are used to keep state, but are very simple in the operations they do. They usually only provide plain getters and setters to access to

their fields. Defining a new data class is very easy:

data class Student(var name:String,var Roll no:Int,var Address:String)

1. Creating New Project in Kotlin

• Open Android Studio.
• Go to File => New => New Project.Give Name To your application. Then, check Include Kotlin Support and click next button.
• Select minimum SDK you need. However, we have selected 21 as minimum SDK. Then, click next button.
• Then, select Empty Activity => click next => click finish.

2. For Custom ListView We need two XML file main xml file contain listView and Other Contain a Single ROW which we want to Show in ListView.Here we Have Two XML file

1.  main_activity.xml
2.  list_row.xml

main_activity.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:orientation="vertical"
    tools:context=".MainActivity">

    <ListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

list_row.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="4dp">


    <TextView
        android:id="@+id/tvName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:gravity="center"
        android:padding="4dp"
        android:text="Name :"
        android:textColor="@android:color/black"
        android:textSize="22sp" />

    <TextView
        android:id="@+id/name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="5dp"
        android:layout_toEndOf="@+id/tvName"
        android:gravity="center"
        android:padding="4dp"
        android:textColor="@color/colorPrimary"
        android:textSize="22sp" />

    <TextView
        android:id="@+id/tvId"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignStart="@+id/tvName"
        android:layout_marginTop="35dp"
        android:gravity="center"
        android:padding="4dp"
        android:text="Id :"
        android:textColor="@android:color/black"
        android:textSize="18sp" />

    <TextView
        android:id="@+id/id"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/name"
        android:layout_alignTop="@+id/tvId"
        android:gravity="center"
        android:padding="4dp"
        android:textColor="@color/colorPrimary"
        android:textSize="18sp" />

</RelativeLayout>

3. MainActivity.kt

package com.dharmendra.dataclass

import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.widget.ListView
import android.widget.Toast
import java.util.*

class MainActivity : AppCompatActivity() {

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

        //Find View By Id For Listview
        val listView = findViewById<ListView>(R.id.listView)


        //Array That contain names which we add to our DataModel Class
        val names = arrayOf("Dharmendra", "Vishal", "Sachin", "Raj", "Jatin", "Krishank", "Rishu")

        //Initialize ArrayList of DataModel Class
        var list = ArrayList<DataModel>()


        //For loop that add name From names Array and index as Id in DataModel Class
        //Add object of DataModel in to ArrayList

        for (i in 0 until names.size) {

            val myData = DataModel(i, names[i])

            list.add(myData)

        }

        //We Have Created Custom Adapter Class in that we pass Context,ArrayList of DataModel
        val customAdapter = CustomAdapter(this, list)

        //Set Adapter to ArrayList
        listView.adapter = customAdapter

        //On Click for ListView Item
        listView.setOnItemClickListener { parent, view, position, id ->

            val name = customAdapter.getItem(position).name
            val id = customAdapter.getItem(position).id

            Toast.makeText(this, "Name:$name\n Id: $id", Toast.LENGTH_LONG).show()
        }


    }


}


//DataModel Class which take and store id and name
data class DataModel(var id: Int, var name: String)

4. Now We have to Create Class CustomAdapter.Right Click on Package name---->New--->Kotlin File/Class.

Now Select Class in Kind and Add name of Class.Here Our Class name is CustomAdapter.

5. After Class is Created add parameter to Class(passed in Main Activity) and extend with BaseAdapter()

Ex:

class CustomAdapter(context: Context,list: ArrayList<DataModel>) : BaseAdapter() {

..

..

..

}

You will get Some Error Put Your Cursor on Red line And Press Alt+Enter and click on Implement Members and Select All Methods and click Ok.

CustomAdapter.kt

package com.dharmendra.dataclass

import android.app.Activity
import android.content.Context
import android.view.View
import android.view.ViewGroup
import android.widget.BaseAdapter
import android.widget.TextView


/*We Have Created Constructor of Custom Adapter and Pass
                context
                ArrayList<DataModel> which Contain our Data
                */

//Here We extend over Adapter With BaseAdapter()


class CustomAdapter(context: Context, list: ArrayList<DataModel>) : BaseAdapter() {


    //Passing Values to Local Variables

    private var list = list
    private var context = context


    //Auto Generated Method

    override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View? {

        var myView = convertView
        val holder: ViewHolder

        if (convertView == null) {


            //If Over View is Null than we Inflater view using Layout Inflater

            val mInflater = (context as Activity).layoutInflater

            //Inflating our list_row.

            myView = mInflater.inflate(R.layout.list_row, parent, false)

            //Create Object of ViewHolder Class and set our View to it

            holder = ViewHolder()

            //Find view By Id For all our Widget taken in list_row.

            /*Here !! are use for non-null asserted two prevent From null.
             you can also use Only Safe (?.)

            */


            holder.name = myView!!.findViewById(R.id.name)
            holder.id = myView.findViewById(R.id.id)

            //Set A Tag to Identify our view.

            myView.setTag(holder)


        } else {

            //If Ouer View in not Null than Just get View using Tag and pass to holder Object.

            holder = myView!!.getTag() as ViewHolder
        }


        //Getting our data at position of List
        val data = getItem(position)


        //Set Name to our TextView
        holder.name!!.text = data.name

        //Set Id to our TextView
        holder.id!!.text = data.id.toString()


        return myView
    }

    //Auto Generated Method

    override fun getItem(position: Int): DataModel {
        //Return the Data at Position of ArrayList.
        return list.get(position)
    }


    //Auto Generated Method

    override fun getItemId(position: Int): Long {
        return 0
    }

    //Auto Generated Method

    override fun getCount(): Int {

        //Return Size Of ArrayList
        return list.size
    }

    //Create A class To hold over View like we taken in list_row.xml
    class ViewHolder {

        var name: TextView? = null
        var id: TextView? = null

    }
}

Output:-