android kotlin - GridView item height

MainActivity.kt

package com.example.jetpack

import android.content.Context
import android.graphics.Color
import android.os.Bundle
import android.util.TypedValue
import android.view.Gravity
import android.view.View
import android.view.ViewGroup
import android.widget.ArrayAdapter
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*


class MainActivity : AppCompatActivity() {

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

        // mutable list of plants to populate grid view
        val list = mutableListOf(
            "Catalina ironwood",
            "Cabinet cherry",
            "Pale corydalis",
            "Pink corydalis",
            "Belle Isle cress",
            "Orange coneflower",
            "Coast polypody",
            "Water fern"
        )

        // set the grid view item height in dp and convert it to pixels
        val itemHeight = 90.dpToPixels(this)


        // array adapter for grid view
        val adapter = object : ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1,list) {
            override fun getView(
                position: Int, convertView: View?,
                parent: ViewGroup
            ): View {

                return (super.getView(position, convertView, parent) as TextView)
                    .apply {
                        text = list[position]
                        gravity = Gravity.CENTER

                        // grid view vertical spacing, horizontal spacing and
                        // item background color together make border between items
                        setBackgroundColor(Color.parseColor("#7DF9FF"))

                        // set grid view item height in pixels
                        layoutParams.height = itemHeight
                    }
            }
        }

        gridView.adapter = adapter


        // set grid view item click listener
        gridView.setOnItemClickListener { adapterView, view, i, l ->
            // get grid view clicked item text
            val selectedItem = adapterView.getItemAtPosition(i).toString()
            textView.text = selectedItem
        }
    }
}


// extension function to convert dp to equivalent pixels
fun Int.dpToPixels(context: Context):Int = TypedValue.applyDimension(
    TypedValue.COMPLEX_UNIT_DIP,this.toFloat(),context.resources.displayMetrics
).toInt()

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:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:background="#F0FFFF">

    <GridView
        android:id="@+id/gridView"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:background="#8BA8B7"
        android:horizontalSpacing="3dp"
        android:numColumns="2"
        android:verticalSpacing="3dp"
        app:layout_constraintEnd_toEndOf="parent"
        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_marginTop="16dp"
        android:textColor="#004F98"
        android:textSize="30sp"
        android:fontFamily="sans-serif-condensed-medium"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/gridView"
        tools:text="TextView" />

</androidx.constraintlayout.widget.ConstraintLayout>