ScrollableList

Learn how to efficiently display a list of text in a RecyclerView and understand its architecture.

activity_main

• RecyclerView widget helps you display a list of data.
• RecyclerView comes with built in LayoutManagers. RecyclerView delegates how items are laid out to LayoutManagers.

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="vertical"
        app:layoutManager="LinearLayoutManager"
        />
</FrameLayout>

list_item

• Use the Material Components for Android library to have your app more easily follow the recommended Material Design guidelines.
• Use MaterialCardView to display content in a Material card.

<?xml version="1.0" encoding="utf-8"?>
<com.google.android.material.card.MaterialCardView  xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp">

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <ImageView
            android:layout_width="match_parent"
            android:layout_height="194dp"
            android:id="@+id/item_image"
            android:importantForAccessibility="no"
            android:scaleType="centerCrop" />

        <TextView
            android:id="@+id/item_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="16dp"
            android:textAppearance="?attr/textAppearanceHeadline6" />

    </LinearLayout>

</com.google.android.material.card.MaterialCardView>

Model

• Use resource annotations to help ensure that the right type of resource ID is passed into a class constructor.

data class Affirmation(
    @StringRes val stringResourceId: Int,
    @DrawableRes val imageResourceId: Int
    )

Datasource

class Datasource {

    fun loadAffirmations(): List<Affirmation> {
        return listOf<Affirmation>(
            Affirmation(R.string.affirmation1, R.drawable.image1),
            Affirmation(R.string.affirmation2, R.drawable.image2),
            Affirmation(R.string.affirmation3, R.drawable.image3),
            Affirmation(R.string.affirmation4, R.drawable.image4),
            Affirmation(R.string.affirmation5, R.drawable.image5),
            Affirmation(R.string.affirmation6, R.drawable.image6),
            Affirmation(R.string.affirmation7, R.drawable.image7),
            Affirmation(R.string.affirmation8, R.drawable.image8),
            Affirmation(R.string.affirmation9, R.drawable.image9),
            Affirmation(R.string.affirmation10, R.drawable.image10),
        )
}

To implement the adapter

RecyclerView uses the adapter pattern to adapt and display the data.
ViewHolder creates and holds the views for RecyclerView.

• Create a custom ViewHolder class that represents a single list item view. Extend from RecyclerView.ViewHolder class.
• Modify the ItemAdapter class to extend from the RecyclerView.Adapter class with the custom ViewHolder class.
• Implement these methods within the adapter: getItemsCount(), onCreateViewHolder(), and onBindViewHolder().

class ItemAdapter(
    private val context: Context,
    private val dataset: List<Affirmation>
) : RecyclerView.Adapter<ItemAdapter.ItemViewHolder>() {

    class ItemViewHolder(private val view: View) : RecyclerView.ViewHolder(view) {
        val textView: TextView = view.findViewById(R.id.item_title)
        val imageView: ImageView = view.findViewById(R.id.item_image)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ItemViewHolder {
        val adapterLayout = LayoutInflater.from(parent.context)
            .inflate(R.layout.list_item, parent, false)
        return ItemViewHolder(adapterLayout)
    }

    override fun onBindViewHolder(holder: ItemViewHolder, position: Int) {
        val item = dataset[position]
        holder.textView.text = context.resources.getString(item.stringResourceId)
        holder.imageView.setImageResource(item.imageResourceId)
    }

    override fun getItemCount(): Int {
        return dataset.size
    }
}