Android - Build a Book Library App using Kotlin

package com.gtappdevelopers.kotlingfgproject

data class BookRVModal(
    // creating string, int and array list
    // variables for our book details
    var title: String,
    var subtitle: String,
    var authors: ArrayList<String>,
    var publisher: String,
    var publishedDate: String,
    var description: String,
    var pageCount: Int,
    var thumbnail: String,
    var previewLink: String,
    var infoLink: String,
    var buyLink: String
)

package com.gtappdevelopers.kotlingfgproject

import android.content.Context
import android.content.Intent
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import com.squareup.picasso.Picasso

class BookRVAdapter(
    // on below line we are passing variables
    // as course list and context
    private var bookList: ArrayList<BookRVModal>,
    private var ctx: Context
) : RecyclerView.Adapter<BookRVAdapter.BookViewHolder>() {
    override fun onCreateViewHolder(
        parent: ViewGroup,
        viewType: Int
    ): BookRVAdapter.BookViewHolder {
        // this method is use to inflate the layout file 
        // which we have created for our recycler view.
        // on below line we are inflating our layout file.
        val itemView = LayoutInflater.from(parent.context).inflate(
            R.layout.book_item,
            parent, false
        )
        // at last we are returning our view holder 
        // class with our item View File.
        return BookRVAdapter.BookViewHolder(itemView)
    }

    override fun onBindViewHolder(holder: BookRVAdapter.BookViewHolder, position: Int) {
        val bookInfo = bookList.get(position)
        // below line is use to set image from URL in our image view.
        Picasso.get().load(bookInfo.thumbnail).into(holder.bookIV);
        holder.bookTitleTV.text = bookInfo.title
        holder.bookPagesTV.text = "Pages : " + bookInfo.pageCount

        // below line is use to add on click listener for our item of recycler view.
        holder.itemView.setOnClickListener {
            // inside on click listener method we are calling a new activity
            // and passing all the data of that item in next intent.
            val i = Intent(ctx, BookDetailsActivity::class.java)
            i.putExtra("title", bookInfo.title)
            i.putExtra("subtitle", bookInfo.subtitle)
            i.putExtra("authors", bookInfo.authors)
            i.putExtra("publisher", bookInfo.publisher)
            i.putExtra("publishedDate", bookInfo.publishedDate)
            i.putExtra("description", bookInfo.description)
            i.putExtra("pageCount", bookInfo.pageCount)
            i.putExtra("thumbnail", bookInfo.thumbnail)
            i.putExtra("previewLink", bookInfo.previewLink)
            i.putExtra("infoLink", bookInfo.infoLink)
            i.putExtra("buyLink", bookInfo.buyLink)

            // after passing that data we are
            // starting our new  intent.
            ctx.startActivity(i)
        }

    }

    override fun getItemCount(): Int {
        return bookList.size
    }

    class BookViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        // on below line we are initializing our 
        // course name text view and our image view.
        val bookTitleTV: TextView = itemView.findViewById(R.id.idTVBookName)
        val bookPagesTV: TextView = itemView.findViewById(R.id.idTVBookPages)
        val bookIV: ImageView = itemView.findViewById(R.id.idIVBook)
    }
}

package com.gtappdevelopers.kotlingfgproject

import android.content.Intent
import android.net.Uri
import android.os.Bundle
import android.widget.Button
import android.widget.ImageView
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import com.squareup.picasso.Picasso

class BookDetailsActivity : AppCompatActivity() {

    // creating variables for strings,text view,
    // image views and button.
    lateinit var titleTV: TextView
    lateinit var subtitleTV: TextView
    lateinit var publisherTV: TextView
    lateinit var descTV: TextView
    lateinit var pageTV: TextView
    lateinit var publisherDateTV: TextView
    lateinit var previewBtn: Button
    lateinit var buyBtn: Button
    lateinit var bookIV: ImageView


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_book_details)
        
        // initializing our variables.
        titleTV = findViewById(R.id.idTVTitle)
        subtitleTV = findViewById(R.id.idTVSubTitle)
        publisherTV = findViewById(R.id.idTVpublisher)
        descTV = findViewById(R.id.idTVDescription)
        pageTV = findViewById(R.id.idTVNoOfPages)
        publisherDateTV = findViewById(R.id.idTVPublishDate)
        previewBtn = findViewById(R.id.idBtnPreview)
        buyBtn = findViewById(R.id.idBtnBuy)
        bookIV = findViewById(R.id.idIVbook)

        // getting the data which we have passed from our adapter class.
        val title = getIntent().getStringExtra("title")
        val subtitle = getIntent().getStringExtra("subtitle")
        val publisher = getIntent().getStringExtra("publisher")
        val publishedDate = getIntent().getStringExtra("publishedDate")
        val description = getIntent().getStringExtra("description")
        val pageCount = getIntent().getIntExtra("pageCount", 0)
        val thumbnail = getIntent().getStringExtra("thumbnail")
        val previewLink = getIntent().getStringExtra("previewLink")
        val infoLink = getIntent().getStringExtra("infoLink")
        val buyLink = getIntent().getStringExtra("buyLink")

        // after getting the data we are setting 
        // that data to our text views and image view.
        titleTV.setText(title)
        subtitleTV.setText(subtitle)
        publisherTV.setText(publisher)
        publisherDateTV.setText("Published On : " + publishedDate)
        descTV.setText(description)
        pageTV.setText("No Of Pages : " + pageCount)
        Picasso.get().load(thumbnail).into(bookIV)

        // adding on click listener for our preview button.
        previewBtn.setOnClickListener {
            if (previewLink.isNullOrEmpty()) {
                // below toast message is displayed 
                // when preview link is not present.
                Toast.makeText(
                    this@BookDetailsActivity,
                    "No preview Link present",
                    Toast.LENGTH_SHORT
                )
                    .show()
            }
            // if the link is present we are opening
            // that link via an intent.
            val uri: Uri = Uri.parse(previewLink)
            val i = Intent(Intent.ACTION_VIEW, uri)
            startActivity(i)
        }

        // adding click listener for buy button
        buyBtn.setOnClickListener {
            if (buyLink.isNullOrEmpty()) {
                // below toast message is displaying 
                // when buy link is empty.
                Toast.makeText(
                    this@BookDetailsActivity,
                    "No buy page present for this book",
                    Toast.LENGTH_SHORT
                ).show()
            }
            // if the link is present we are opening
            // the link via an intent.
            val uri = Uri.parse(buyLink)
            val i = Intent(Intent.ACTION_VIEW, uri)
            startActivity(i)
        }

    }
}

package com.gtappdevelopers.kotlingfgproject

import android.os.Bundle
import android.view.View
import android.widget.EditText
import android.widget.ImageButton
import android.widget.ProgressBar
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.GridLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.android.volley.Request
import com.android.volley.RequestQueue
import com.android.volley.toolbox.JsonObjectRequest
import com.android.volley.toolbox.Volley

class MainActivity : AppCompatActivity() {

    // on below line we are creating variables.
    lateinit var mRequestQueue: RequestQueue
    lateinit var booksList: ArrayList<BookRVModal>
    lateinit var loadingPB: ProgressBar
    lateinit var searchEdt: EditText
    lateinit var searchBtn: ImageButton

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        
        // on below line we are initializing 
        // our variable with their ids.
        loadingPB = findViewById(R.id.idLoadingPB)
        searchEdt = findViewById(R.id.idEdtSearchBooks)
        searchBtn = findViewById(R.id.idBtnSearch)

        // adding click listener for search button
        searchBtn.setOnClickListener {
            loadingPB.visibility = View.VISIBLE
            // checking if our edittext field is empty or not.
            if (searchEdt.text.toString().isNullOrEmpty()) {
                searchEdt.setError("Please enter search query")
            }
            // if the search query is not empty then we are
            // calling get book info method to load all
            // the books from the API.
            getBooksData(searchEdt.getText().toString());
        }

    }

    private fun getBooksData(searchQuery: String) {
        // creating a new array list.
        booksList = ArrayList()

        // below line is use to initialize
        // the variable for our request queue.
        mRequestQueue = Volley.newRequestQueue(this@MainActivity)

        // below line is use to clear cache this
        // will be use when our data is being updated.
        mRequestQueue.cache.clear()

        // below is the url for getting data from API in json format.
        val url = "https://www.googleapis.com/books/v1/volumes?q=$searchQuery"

        // below line we are  creating a new request queue.
        val queue = Volley.newRequestQueue(this@MainActivity)

        // on below line we are creating a variable for request 
        // and initializing it with json object request
        val request = JsonObjectRequest(Request.Method.GET, url, null, { response ->
            loadingPB.setVisibility(View.GONE);
            // inside on response method we are extracting all our json data.
            try {
                val itemsArray = response.getJSONArray("items")
                for (i in 0 until itemsArray.length()) {
                    val itemsObj = itemsArray.getJSONObject(i)
                    val volumeObj = itemsObj.getJSONObject("volumeInfo")
                    val title = volumeObj.optString("title")
                    val subtitle = volumeObj.optString("subtitle")
                    val authorsArray = volumeObj.getJSONArray("authors")
                    val publisher = volumeObj.optString("publisher")
                    val publishedDate = volumeObj.optString("publishedDate")
                    val description = volumeObj.optString("description")
                    val pageCount = volumeObj.optInt("pageCount")
                    val imageLinks = volumeObj.optJSONObject("imageLinks")
                    val thumbnail = imageLinks.optString("thumbnail")
                    val previewLink = volumeObj.optString("previewLink")
                    val infoLink = volumeObj.optString("infoLink")
                    val saleInfoObj = itemsObj.optJSONObject("saleInfo")
                    val buyLink = saleInfoObj.optString("buyLink")
                    val authorsArrayList: ArrayList<String> = ArrayList()
                    if (authorsArray.length() != 0) {
                        for (j in 0 until authorsArray.length()) {
                            authorsArrayList.add(authorsArray.optString(i))
                        }
                    }

                    // after extracting all the data we are
                    // saving this data in our modal class.
                    val bookInfo = BookRVModal(
                        title,
                        subtitle,
                        authorsArrayList,
                        publisher,
                        publishedDate,
                        description,
                        pageCount,
                        thumbnail,
                        previewLink,
                        infoLink,
                        buyLink
                    )

                    // below line is use to pass our modal
                    // class in our array list.
                    booksList.add(bookInfo)

                    // below line is use to pass our
                    // array list in adapter class.
                    val adapter = BookRVAdapter(booksList, this@MainActivity)

                    // below line is use to add linear layout
                    // manager for our recycler view.
                    val layoutManager = GridLayoutManager(this, 3)
                    val mRecyclerView = findViewById<RecyclerView>(R.id.idRVBooks) as RecyclerView

                    // in below line we are setting layout manager and
                    // adapter to our recycler view.
                    mRecyclerView.layoutManager = layoutManager
                    mRecyclerView.adapter = adapter
                }
            } catch (e: Exception) {
                e.printStackTrace()
            }


        }, { error ->
            // in this case we are simply displaying a toast message.
            Toast.makeText(this@MainActivity, "No books found..", Toast.LENGTH_SHORT)
                .show()
        })
        // at last we are adding our
        // request to our queue.
        queue.add(request)

    }
}