Android kotlin: How to iterate over the characters in a string

Iterating Over Strings in Android with Kotlin

This code demonstrates two ways to iterate over the characters in a string within an Android application written in Kotlin. The application presents two buttons:

• "Iterate over string": Clicking this button iterates through the characters of a string variable without using an index property.
• "Iterate string using index": Clicking this button iterates through the characters using the string's index property.

Both button clicks update a TextView element, displaying the characters of the string one by one on separate lines.

Breakdown and Functionality

The code consists of two main parts: the MainActivity.kt file containing the Kotlin code and the activity_main.xml file defining the user interface layout.

MainActivity.kt:

1. Imports: The code imports necessary libraries for building the user interface and working with resources.
2. Class Definition: The MainActivity class inherits from AppCompatActivity, which is the base class for most activities in Android applications.
3. onCreate Method: This method is called when the activity is first created. Here:
   • The layout (activity_main.xml) is inflated using setContentView.
   • References to UI elements (buttons and TextView) are obtained using findViewById.
   • A string variable name is declared and initialized with the value "Innee".
   • Button click listeners are set for both buttons. These handle user interaction and update the TextView.
     • Clicking the first button iterates through the characters of name using a for loop that iterates over each character directly.
     • Clicking the second button iterates through the characters using a for loop that iterates over the indices of name. The character at each index is then accessed using the indexer [].

activity_main.xml:

This file defines the layout of the activity using XML. It includes:

• A LinearLayout as the root layout with vertical orientation.
• Two Button elements corresponding to the functionality of iterating over the string with and without index.
• A TextView element to display the results of the iteration.

Summary

This example showcases two ways to iterate over characters in a string using Kotlin in an Android application. It demonstrates working with UI elements and user interaction to provide a visual representation of the iteration process.

MainActivity.kt

package com.cfsuman.kotlinexamples

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.TextView


class MainActivity : AppCompatActivity() {

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

        // Get the widgets reference from xml layout
        val textView = findViewById<TextView>(R.id.text_view)
        val button = findViewById<Button>(R.id.button);
        val button2 = findViewById<Button>(R.id.button2);

        // The simple string variable
        var name = "Innee"


        // Iterate over a string characters
        button.setOnClickListener{
            textView.text = "Iterate over a string [$name] \n\n"

            // Iterate over a string without index property
            for (letter in name){
                textView.text = textView.text.toString() + letter + "\n"
            }
        }


        // Iterate over a string using index property
        button2.setOnClickListener{
            textView.text = "Iterate over a string [$name] with index property \n\n"

            // Iterate over a string using index property
            for (index in name.indices){
                textView.text = textView.text.toString() + name[index] + "\n"
            }
        }
    }
}

activity_main.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:id="@+id/root_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp"
    >
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Iterate over string"
        />
    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Iterate string using index"
        />
    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text=""
        android:textSize="18sp"
        android:textStyle="bold"
        android:textColor="#ff191d"
        android:layout_marginTop="20dp"
        />
</LinearLayout>