Android ViewHolder pattern

CategoryAdapter.kt

class CategoryAdapter(private val context: Context, private val categories: List<Category>) : BaseAdapter() {

    override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View {
        val categoryView : View
        val holder : ViewHolder
        if (convertView == null) {
            categoryView = LayoutInflater.from(this.context).inflate(R.layout.category_list_item, null)
            holder = ViewHolder()
            holder.categoryImage = categoryView.findViewById(R.id.categoryImage)
            holder.categoryName = categoryView.findViewById(R.id.categoryTitle)
            categoryView.tag = holder
        } else {
            holder = convertView.tag as ViewHolder
            categoryView = convertView
        }
        val category = this.categories[position]
        val resourceId = this.context.resources.getIdentifier(category.image, "drawable", this.context.packageName)
        holder.categoryImage?.setImageResource(resourceId)
        holder.categoryName?.text = category.title
        return categoryView
    }

    override fun getItem(position: Int): Category {
        return this.categories[position]
    }

    override fun getItemId(position: Int): Long {
        return 0
    }

    override fun getCount(): Int {
        return this.categories.count()
    }

    private class ViewHolder {
        var categoryImage : ImageView? = null
        var categoryName : TextView? = null
    }
}