Explore

Lab 1: November 20 2025: Books and Recycler Views

Learning outcomes:

RecyclerView

Adapter

List of custom objects

Navigation to an Edit screen

Updating data

Shared data storage (in memory only)

Recycler view and edit screen: Managing a list of Books.

⁠

Book.kt

BookRepository.kt

item_book.xml

activity_main.xml

BookAdapter.kt

MainActivity.kt

activity_edit_book.xml

EditBookActivity.kt

⁠

Step 1: Book.kt

package com.example.bookapp

data class Book(

var title: String,

var author: String

)

⁠

STEP 2 — Create the Shared Repository

⭐ This removes all complexity.

BookRepository.kt

package com.example.bookapp

object BookRepository {

val books = mutableListOf<Book>()

}

This is our in-memory database.

⁠

STEP 3 — Create the Item Layout

⁠

res/layout/item_book.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"

android:padding="16dp"

android:layout_width="match_parent"

android:layout_height="wrap_content">

<TextView

android:id="@+id/textTitle"

android:textSize="18sp"

android:textStyle="bold"

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

<TextView

android:id="@+id/textAuthor"

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

</LinearLayout>

⁠

STEP 4 — Create the Main Screen Layout

res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"

android:layout_width="match_parent"

android:layout_height="match_parent">

<Button

android:id="@+id/btnAdd"

android:text="Add Book"

android:layout_width="match_parent"

android:layout_height="wrap_content"/>

<androidx.recyclerview.widget.RecyclerView

android:id="@+id/rvBooks"

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"/>

</LinearLayout>

⁠

STEP 5 — Create the Adapter

BookAdapter.kt BookAdapter brings the recycler view to life. takes a list of books and turns each one into a visible row on the screen.

BookAdapter.kt is the code that tells the RecyclerView how to show each book and how to fill each row with data.

package com.example.bookapp

import android.view.LayoutInflater

import android.view.View

import android.view.ViewGroup

import android.widget.TextView

import androidx.recyclerview.widget.RecyclerView

class BookAdapter(

// The constructor lets the Activity tell the adapter

// what should happen when a book is clicked.

// Here you are passing into the constructor a Function - A BEHAVIOR

// It returns a Behavior, not a value

// onItemClick — saves the function so the adapter can use it inside the ViewHolder.

// When the user clicks a row, open the EditBookActivity

// and tell it which row was clicked

private val onItemClick: (Int) -> Unit

) : RecyclerView.Adapter<BookAdapter.BookViewHolder>() {

inner class BookViewHolder(view: View) : RecyclerView.ViewHolder(view) {

val title: TextView = view.findViewById(R.id.textTitle)

val author: TextView = view.findViewById(R.id.textAuthor)

init {

view.setOnClickListener {

onItemClick(bindingAdapterPosition)

}

// This means: “When someone taps this row, call the function the Activity gave me,

// and tell it my position.”

}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): BookViewHolder {

val view = LayoutInflater.from(parent.context)

.inflate(R.layout.item_book, parent, false)

return BookViewHolder(view)

}

override fun onBindViewHolder(holder: BookViewHolder, position: Int) {

val book = BookRepository.books[position]

holder.title.text = book.title

holder.author.text = book.author

}

override fun getItemCount(): Int = BookRepository.books.size

}

⁠

🚀 STEP 6 — Create MainActivity

MainActivity.kt

package com.example.bookapp

import android.content.Intent

import android.os.Bundle

import android.widget.Button

import androidx.appcompat.app.AppCompatActivity

import androidx.recyclerview.widget.LinearLayoutManager

import androidx.recyclerview.widget.RecyclerView

class MainActivity : AppCompatActivity() {

Want to print your doc?
This is not the way.

Try clicking the ··· in the right corner or using a keyboard shortcut (

CtrlP

) instead.