Make Your First Android App with Kotlin (Android Kotlin Tutorial for Beginners) (Code)

Kotlin is a new official language for Android development. It’s certainly a step towards safer, readable and quicker to write code.

Kotlin supports properties, you don’t have to call “findViewById()”, and it also tries to get rid of the dreaded null reference exception.

Whether you are a complete beginner who is just starting out in Android app development or you are a Java Android developer looking for something new, you cannot go wrong with Kotlin in Android.

This post contains all the code that’s been written in this YouTube video.

MainActivity.kt

package com.resocoder.firstapptut

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.SeekBar
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

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

        val initialTextViewTranslationY = textView_progress.translationY

        seekBar.setOnSeekBarChangeListener(object: SeekBar.OnSeekBarChangeListener{
            override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
                textView_progress.text = progress.toString()

                val translationDistance = (initialTextViewTranslationY +
                        progress * resources.getDimension(R.dimen.text_anim_step) * -1)

                textView_progress.animate().translationY(translationDistance)
                if (!fromUser)
                    textView_progress.animate().setDuration(500).rotationBy(360f)
                            .translationY(initialTextViewTranslationY)
            }

            override fun onStartTrackingTouch(seekBar: SeekBar?) {

            }

            override fun onStopTrackingTouch(seekBar: SeekBar?) {

            }

        })

        button_reset.setOnClickListener { v ->
            seekBar.progress = 0
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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="com.resocoder.firstapptut.MainActivity">

    <TextView
        android:id="@+id/textView_progress"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0"
        android:textSize="60sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.369" />

    <SeekBar
        android:id="@+id/seekBar"
        android:layout_width="239dp"
        android:layout_height="40dp"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:max="10"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView_progress" />

    <Button
        android:id="@+id/button_reset"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="Reset"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/seekBar"
        app:layout_constraintVertical_bias="0.112" />

</android.support.constraint.ConstraintLayout>

dimens.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <dimen name="text_anim_step">5dp</dimen>
</resources>