Is there a way to use Recycler View in Kotlin?

Question

I tried using recycler view but it is giving me some error

Can i use scrollView Instead ,are they same? How can I initialize and use a RecyclerView in Kotlin for an Android app? I'm new to Kotlin and struggling with setting up a RecyclerView to display a list of items. I need a basic example or guidance on how to start. Any help?

Answer 1

Efficient Recycling of Views: The primary advantage of RecyclerView is its ability to recycle views as you scroll through the list. This means it reuses view holders for new items that become visible, significantly reducing memory consumption and improving performance, especially for large or complex lists. ScrollView, on the other hand, does not recycle views; it simply scrolls through the content, which can lead to performance issues for large datasets. Yes,i have providedsome sample to help ,refer to this:

<androidx.recyclerview.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

https://pastebin.com/iyebvvFN 
https://pastebin.com/D0j9Nx9i
 val intent = Intent(this, MainActivity2::class.java).apply {
        putExtra("score", score)
        putStringArrayListExtra("ans", ArrayList(urans))
    }
    startActivity(intent)
}

#ON NEXT PAGE val getans:ArrayList?=intent.getStringArrayListExtra("ans") val answersText = getans?.joinToString(separator = "\n") ?: "No answers provided" val score=intent.getIntExtra("score",0)

https://pastebin.com/0Mf3VTx4

Answer 2

developer.android.com usually has good explanations for importants concepts such as this one : https://developer.android.com/develop/ui/views/layout/recyclerview

Answer 3

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import net.objecthunter.exp4j.ExpressionBuilder

class MainActivity : AppCompatActivity() {

    lateinit var resultTextView: TextView
    var lastNumeric: Boolean = false

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

        resultTextView = findViewById(R.id.textViewResult)
        val buttonOne: Button = findViewById(R.id.buttonOne)
        val buttonTwo: Button = findViewById(R.id.buttonTwo)
        val buttonThree: Button = findViewById(R.id.buttonThree)
        val buttonFour: Button = findViewById(R.id.buttonFour)
        val buttonFive: Button = findViewById(R.id.buttonFive)
        val buttonSix: Button = findViewById(R.id.buttonSix)
        val buttonSeven: Button = findViewById(R.id.buttonSeven)
        val buttonEight: Button = findViewById(R.id.buttonEight)
        val buttonNine: Button = findViewById(R.id.buttonNine)
        val buttonZero: Button = findViewById(R.id.buttonZero)

        val buttonAdd: Button = findViewById(R.id.buttonAdd)
        val buttonSubtract: Button = findViewById(R.id.buttonSubtract)
        val buttonMultiply: Button = findViewById(R.id.buttonMultiply)
        val buttonDivide: Button = findViewById(R.id.buttonDivide)
        val buttonEquals: Button = findViewById(R.id.buttonEquals)
        val buttonClear: Button = findViewById(R.id.buttonClear)

        // Initialize buttons and set their onClickListeners
        val buttons = arrayOf(buttonOne, buttonTwo, buttonThree, buttonFour, buttonFive,
            buttonSix, buttonSeven, buttonEight, buttonNine, buttonZero)

        buttons.forEach { button ->
            button.setOnClickListener { onDigitPressed((it as Button).text.toString()) }
        }

        buttonAdd.setOnClickListener { onOperationPressed("+") }
        buttonSubtract.setOnClickListener { onOperationPressed("-") }
        buttonMultiply.setOnClickListener { onOperationPressed("*") }
        buttonDivide.setOnClickListener { onOperationPressed("/") }

        buttonClear.setOnClickListener {
            resultTextView.text = ""
            lastNumeric = false
        }

        buttonEquals.setOnClickListener {
            onEquals()
        }
    }

    private fun onDigitPressed(digit: String) {
        resultTextView.append(digit)
        lastNumeric = true
    }

    private fun onOperationPressed(operation: String) {
        if (lastNumeric && !isOperatorAdded(resultTextView.text.toString())) {
            resultTextView.append(operation)
            lastNumeric = false
        }
    }

    private fun onEquals() {
        if (lastNumeric) {
            val expression = ExpressionBuilder(resultTextView.text.toString()).build()
            try {
                val result = expression.evaluate()
                resultTextView.text = result.toString()
            } catch (ex: Exception) {
                resultTextView.text = "Error"
                lastNumeric = false
            }
        }
    }

    private fun isOperatorAdded(value: String): Boolean {
        return if (value.startsWith("-")) {
            false
        } else {
            value.contains("/") || value.contains("*") || value.contains("+") || value.contains("-")
        }
    }
}