Sunday, October 20, 2019

android kotlin - Difference between takeWhile and filter

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)

        val list = mutableListOf('a','a','b','b','c','d','a','e','b','f','a','a','b','g','h','i')

        btn.setOnClickListener {
            textView.text = " List: "
            list.forEach { textView.append("$it, ") }

            // takeWhile only returns by matching condition and take first elements of the list
            val taken = list.takeWhile { it == 'a' }
            textView.append("\n\nlist.takeWhile { it == 'a' }")

            taken.forEach {
                textView.append("\n$it")
            }

            val filtered = list.filter { it == 'a' }
            textView.append("\n\nlist.filter { it == 'a' }")
            filtered.forEach {
                textView.append("\n$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="Take While vs Filter"
        app:layout_constraintStart_toStartOf="parent"
        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>
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