Saturday, October 26, 2019

android kotlin - List groupBy 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 = listOf("RED","GREEN","YELLOW","MAGENTA","PINK","WHITE","BLACK","BLUE",
            "SALMON","MAROON","PURPLE")

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

            // Iterate through the list
            list.forEach {
                textView.append("\n$it")
            }
        }

        btnGroupBy.setOnClickListener {
            // Groups the colors by it length
            val groups:Map<Int,List<String>> = list.groupBy { it.length }

            textView.text = ""
            groups.forEach{
                val length = it.key
                val colors = it.value

                textView.append("\n${colors.size} Color(s) length is $length : ")
                colors.forEach {
                    textView.append("$it, ")
                }
            }
        }
    }
}
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/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/btnGroupBy"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="groupBy"
        app:layout_constraintStart_toEndOf="@+id/btn"
        app:layout_constraintTop_toTopOf="parent" />
    <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>