ListView component

ListView displays a vertically-scrollable collection of views, where each view is positioned immediatelybelow the previous view in the list.

At nowadays ListView is used as part of other ui elements to show dropdown as in AutoCompleteTextView. And for displaying the list, a more flexible and efficient RecyclerView is used.

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">
<ListView
    android:id="@+id/listView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"></ListView>
</FrameLayout>

You must specify adapter to provide data for ListView. Adapter also responsible for views of items in ListView.

listView = findViewById(R.id.listView)

val items = mutableListOf(
    "item0", "item1", "item2", "item3", "item4",
    "item5", "item6", "item7", "item8", "item9"
    )
        
val adapter = MyAdapter(this, items)

You can handle a user click on an item or a long click on an item.

listView.setOnItemClickListener { adapterView: AdapterView<*>, itemView: View, 
                         itemPosition: Int, itemId: Long ->
    Toast.makeText(
        this@MyActivity,
        // adapterView.getItemAtPosition(itemPosition).toString()
        adapter.getItem(itemPosition), 
        Toast.LENGTH_SHORT
        )
        .show()
}

adapters

You can make custom adapter by extending the BaseAdapter class.

If the dataset has changed, the adapter must call the notifyDataSetChanged() method, as the addItem() method in the example does.

To reuse views in a long list check convertView for null in getView() method.

class MyAdapter(
        context: Context, private var src: MutableList<String>,
        private val idResLayout: Int = android.R.layout.simple_list_item_1,
        private val idResTextView: Int = android.R.id.text1
    ) : BaseAdapter() {
    
    private val mInflater: LayoutInflater

    init {
        mInflater = LayoutInflater.from(context)
    }

    override fun getCount(): Int {
        return src.size
    }

    override fun getItem(position: Int): String {
        return src[position]
    }

    override fun getItemId(position: Int): Long {
        return src[position].hashCode().toLong()
    }

    override fun getView(position: Int, convertView: View?, 
                    parent: ViewGroup?): View {
        val item = getItem(position)
        val v = convertView ?: mInflater.inflate(idResLayout, parent, false)

        when {
            v is TextView -> {
                v.text = item
            }

            v is ViewGroup && idResTextView > 0 -> {
                 val tv: TextView = v.findViewById(idResTextView)
                 tv.text = item
            }
        }

            return v
        }

    fun addItem(newItem: String) {
        src.add(newItem)
        notifyDataSetChanged()
    }
}

Android provides some other adapter classes.

headers/footers

HeaderViewListAdapter allows you to specify headers and footers for your ListView.

In the custom adapter you must return count of items with the header and footer items and return proper view for them.

// suppose we want show "load more" footer
class MyAdapter(
    context: Context, private var src: MutableList<String>,
    private val idResLayout: Int = R.layout.test_item,
    private val idResTextView: Int = R.id.itemText
): BaseAdapter() {

    var footerVisible: Boolean = false
        set(value) {
            field = value
            notifyDataSetChanged()
        }
        
    override fun getCount(): Int {
        return src.size + if (footerVisible) 1 else 0
    }
    
    override fun getView(position: Int, convertView: View?, parent: ViewGroup?)
             : View {
        if(footerVisible && position==getCount()-1){
            return getFooterView()
        }
     // ...   
    }    

// ...
}

filtering

In some cases, you need to add a Filterable interface to your adapter, for example when you are working with AutoCompleteTextView.

class SearchSuggestionsAdapter(
    context: Context,
    private val src: RealmResults<Suggestion>,
    private val idResLayout: Int = android.R.layout.simple_list_item_1,
    private val idResTextView: Int = android.R.id.text1
) : BaseAdapter(),
    Filterable {

    private var mData: List<Suggestion>? = null

    private val mFilter = object : Filter() {

        override fun performFiltering(constraint: CharSequence?): 
                FilterResults {
            return FilterResults().apply{
                // typically perform filtering here
                // ...
                // values = resultList
                // count = result.size
            } 
        }

        override fun publishResults(constraint: CharSequence?, 
                results: FilterResults?) {
            // in our case do filtering in main thread     
            mData = src.where().contains("text", constraint.toString()).findAll()
            
            notifyDataSetChanged()
        }
    }
    
    override fun getFilter(): Filter {
        return mFilter
    }
    
    // ...
}

The performFiltering() method will be performed in background thread by worker, so it cannot touch ui.

Suppose you work with the Realm db, which uses separate instance of realm for each thread. Creation a new realm instance is very costly. In this case, you can perform filtering in publishResults() method.

Built-in adapters like SimpleAdapter already implement Filterable.

view holder

This is deprecated, use RecyclerView instead ListView.

Item view can be complex and contain multiple views like TextView and ImageView. Calling the findViewById() method is costly. To optimize performance you can use a holder class to keep a view references.

class ViewHolder{
    lateinit var txt : TextView
    lateinit var title : TextView
    lateinit var author : TextView
    // ...
}

Rewrite getView() method of adapter to use ViewHolder

override fun getView(position: Int, 
                 convertView: View?, parent: ViewGroup?): View {
    val item = getItem(position)
    val v = convertView ?: mInflater.inflate(idResLayout, parent, false)

    var vholder : ViewHolder = v.tag?.run {this as ViewHolder } 
                       ?: ViewHolder().apply {
                           txt = v.findViewById(itemTextId)
                           title = v.findViewById(itemTitleId)
                           // ...
                           v.tag = this
                          }

     bindView(vholder, item)
     return v
}

fun bindView(vHolder: ViewHolder, item: MyItemObject){
    vHolder.txt.text = item.text
    vHolder.title.text = item.title
    //...
}