Kotlin Adapter

Basic

This will create a lot of reads, so only good for small data sets

• Create a List View to display your items
• In a separate layout file create an item view
• Create a new file with Kotlin Class, call it XXXAdapter or whatever. eg

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

You will have to override getView, getItem, getItemId, getCount

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

    val context = context
    val categories = categories

    override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View {
        val categoryView :View

        categoryView = LayoutInflater.from(context).inflate(R.layout.category_list_item,null)
      
        val resourceID = context.resources.getIdentifier(categories[position].image,"drawable",context.packageName)
        categoryView.categoryImage.setImageResource(resourceID)
        categoryView.categoryText.text = categories[position].title
        return categoryView
    }

    override fun getItem(position: Int): Any {
        return categories[position]
    }

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

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

Then in MainActivity or where you are calling this from:

class MainActivity : AppCompatActivity() {

    lateinit var adapter:CategoryAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        adapter = CategoryAdapter(this,DataService.categories)
        categoryListView.adapter = adapter
    }
}

Using a Holder

A holder will hold the view for reusing

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

    val context = context
    val categories = categories

    override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View {
        val categoryView :View
        val holder: ViewHolder

        if (convertView == null) { //The first time the views are presented
            categoryView = LayoutInflater.from(context).inflate(R.layout.category_list_item,null)
            holder = ViewHolder()
            holder.categoryImage  = categoryView.findViewById(R.id.categoryImage)
            holder.categoryTitle  = categoryView.findViewById(R.id.categoryText)
            println("I exist for the first time")
            categoryView.tag = holder
        } else {
            holder = convertView.tag as ViewHolder
            categoryView = convertView
            println("Recycled")
        }

        val category = categories[position]

        val resourceID = context.resources.getIdentifier(categories[position].image,"drawable",context.packageName)
        holder.categoryImage?.setImageResource(resourceID)
        holder.categoryTitle?.text = category.title
        return categoryView
    }

    override fun getItem(position: Int): Any {
        return categories[position]
    }

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

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

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