Saturday, November 2, 2019

android kotlin - getOrElse and getOrNull example

MainActivity.kt

package com.example.jetpack

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

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

        // Create a list with values
        val list = mutableListOf("RED","GREEN","YELLOW","WHITE")

        btn.setOnClickListener {
            textView.text = "Colors:\n"

            // Iterate through the list
            list.forEachIndexed { index, color ->
                textView.append("\n${index}. $color")
            }
        }

        btnGetOrElse.setOnClickListener {
            // get the color from index 5 or default value
            // if index is out of range, it returns value from lambda expression
            val atIndex5 = list.getOrElse(
                5, // index
                {list.first()} // default value
            )

            textView.text = "Element at index 5 or default value"
            textView.append("\n\n$atIndex5")
        }


        btnGetOrNull.setOnClickListener {
            // get the color from index 5 or null
            // if the index is out of range then it returns null
            val atIndex4 = list.getOrNull(4)

            textView.text = "Element at index 4 or default value"
            textView.append("\n\n$atIndex4")
        }
    }
}
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">
    <Button
        android:id="@+id/btnGetOrNull"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="getOrElse"
        app:layout_constraintStart_toEndOf="@+id/btnGetOrElse"
        app:layout_constraintTop_toTopOf="parent"
        android:textAllCaps="false" />
    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="List"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <Button
        android:id="@+id/btnGetOrElse"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="getOrNull"
        app:layout_constraintStart_toEndOf="@+id/btn"
        app:layout_constraintTop_toTopOf="parent"
        android:textAllCaps="false" />
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:padding="16dp"
        android:text="List Example"
        android:textAppearance="@style/TextAppearance.AppCompat.Medium"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btn"
        android:textStyle="bold" />
</androidx.constraintlayout.widget.ConstraintLayout>