Challenge 1: A Basic RecyclerView List — Solution

data class Product(val name: String, val price: Double)

// item_product.xml
// <LinearLayout ...>
//   <TextView android:id="@+id/nameText" .../>
//   <TextView android:id="@+id/priceText" .../>
// </LinearLayout>

class ProductAdapter(private val products: List<Product>) :
    RecyclerView.Adapter<ProductAdapter.ProductViewHolder>() {

    class ProductViewHolder(val binding: ItemProductBinding) :
        RecyclerView.ViewHolder(binding.root)

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
        val binding = ItemProductBinding.inflate(
            LayoutInflater.from(parent.context), parent, false
        )
        return ProductViewHolder(binding)
    }

    override fun onBindViewHolder(holder: ProductViewHolder, position: Int) {
        val product = products[position]
        holder.binding.nameText.text = product.name
        holder.binding.priceText.text = "$${product.price}"
    }

    override fun getItemCount() = products.size
}

// MainActivity.kt — inside onCreate
val products = listOf(
    Product("Keyboard", 49.99),
    Product("Mouse", 19.99),
    Product("Monitor", 179.99),
    Product("Webcam", 39.99),
    Product("Headset", 59.99)
)

binding.recyclerView.layoutManager = LinearLayoutManager(this)
binding.recyclerView.adapter = ProductAdapter(products)

Notes:
- onCreateViewHolder only runs enough times to fill the visible screen
  (plus a small buffer) — with 5 items on a typical phone screen, it
  might run all 5 times, or fewer if not all items fit at once; scrolling
  further wouldn't call it again for items already inflated once.
- onBindViewHolder runs once per item as it scrolls into view (and again
  each time a recycled holder is reused for a different position), which
  is why it should only set data on already-existing Views, never
  inflate new ones.
- The RecyclerView itself needs a layoutManager assigned (LinearLayoutManager
  here) before an adapter will actually render anything — a RecyclerView
  with an adapter but no layoutManager shows nothing.