RecyclerView

Displays a scrolling list of elements based on a large data set or data that changes frequently. It is a more flexible vrsion of ListView with advanced features.

Tip: Android studio provides a Fragement (list) template to help with creating a RecyleView.

RecylerView

To display your data in a RecyclerView, you need the following parts:

• Data
  A collection.

• A RecyclerView
  The the overall container that provides the scrolling list of list items.

• Layout for one item of data
  All list items look the same.

• A layout manager
  RecyclerView requires an explicit layout manager to manage the arrangement of list items contained within it. This layout could be vertical, horizontal, or a grid.

• An adapter
  The adapter creates view holders as needed. The adapter also binds the view holders to their data. It does this by assigning the view holder to a position, and calling the adapter's onBindViewHolder() method. That method uses the view holder's position to determine what the contents should be, based on its list position.

• A view holder
  class that contains the view information for displaying one item from the item's layout. Managed by an adapter, created by extending RecyclerView.Adapter. Creates views as needed and binds view holders with data. It does this by assigning the view holder to a position, and calling the adapter's onBindViewHolder() method. That method uses the view holder's position to determine what the contents should be, based on its list position.

Terms

• Adapter: A subclass of RecyclerView.Adapter responsible for providing views that represent items in a data set.
• Position: The position of a data item within an Adapter.
• Index: The index of an attached child view as used in a call to getChildAt(int). Contrast with Position.
• Binding: The process of preparing a child view to display data corresponding to a position within the adapter.
• Recycle (view): A view previously used to display data for a specific adapter position may be placed in a cache for later reuse to display the same type of data again later. This can drastically improve performance by skipping initial layout inflation or construction.
• Scrap (view): A child view that has entered into a temporarily detached state during layout. Scrap views may be reused without becoming fully detached from the parent RecyclerView, either unmodified if no rebinding is required or modified by the adapter if the view was considered dirty.
• Dirty (view): A child view that must be rebound by the adapter before being displayed.

Create a RecyclerView

Add the support library:

build.module(Project:project)

ext.kotlin_version = '1.1.4-2' 
ext.android_support_version = "27.0.2"

build.gradle(Module:app)

implementation 'com.android.support:recyclerview-v7:$android_support_version'

Add RecyclerView to Layout

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

<?xml version="1.0" encoding="utf-8"?>
<!-- A RecyclerView with some commonly used attributes -->
<android.support.v7.widget.RecyclerView
    android:id="@+id/my_recycler_view"
    android:scrollbars="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

</android.support.design.widget.CoordinatorLayout>

swipe refresh alternative

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout 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:id="@+id/charactersView" 
   android:layout_width="match_parent" 
   android:layout_height="match_parent" 
   android:background="@android:color/white" 
   android:fitsSystemWindows="true"> 

   <android.support.v4.widget.SwipeRefreshLayout  
       xmlns:android="http://schemas.android.com/apk/res/android" 
       android:id="@+id/swipeRefreshView" 
       android:layout_width="match_parent" 
       android:layout_height="match_parent"> 

       <android.support.v7.widget.RecyclerView 
           android:id="@+id/recyclerView" 
           android:layout_width="match_parent" 
           android:layout_height="match_parent" 
           android:scrollbars="vertical" /> 

   </android.support.v4.widget.SwipeRefreshLayout> 

   <TextView 
       android:layout_width="match_parent" 
       android:layout_height="wrap_content" 
       android:layout_alignParentBottom="true" 
       android:background="@android:color/white" 
       android:gravity="center" 
       android:text="@string/copyright_notice" /> 
</RelativeLayout>

setup up in code

public class MyActivity extends Activity {
    private RecyclerView mRecyclerView;
    private RecyclerView.Adapter mAdapter;
    private RecyclerView.LayoutManager mLayoutManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_activity);
        mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);

        // use this setting to improve performance if you know that changes
        // in content do not change the layout size of the RecyclerView
        mRecyclerView.setHasFixedSize(true);

        // use a linear layout manager
        mLayoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(mLayoutManager);

        // specify an adapter (see also next example)
        mAdapter = new MyAdapter(myDataset);
        mRecyclerView.setAdapter(mAdapter);
    }
    ...
}

or for a fragment

class RecyclerViewFragment : Fragment() {

    private lateinit var recyclerView: RecyclerView
    private lateinit var dataset: Array<String>

    override fun onCreateView(inflater: LayoutInflater,
                              container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        val rootView = inflater.inflate(R.layout.recycler_view_frag,
                container, false).apply { tag = TAG}

        recyclerView = rootView.findViewById(R.id.recyclerView)

        // LinearLayoutManager is used here, this will layout the elements in a similar fashion
        // to the way ListView would layout elements. The RecyclerView.LayoutManager defines how
        // elements are laid out.
        recycleView.layoutManager = LinearLayoutManager(activity)

        // Set CustomAdapter as the adapter for RecyclerView.
        recyclerView.adapter = CustomAdapter(dataset)

        return rootView
    }

create an adapter

class CustomAdapter(private val dataSet: Array<String>) :
        RecyclerView.Adapter<CustomAdapter.ViewHolder>() {

    /**
     * Provide a reference to the type of views that you are using (custom ViewHolder)
     */
    class ViewHolder(v: View) : RecyclerView.ViewHolder(v) {
        val textView: TextView

        init {
            // Define click listener for the ViewHolder's View.
            v.setOnClickListener { Log.d(TAG, "Element $adapterPosition clicked.") }
            textView = v.findViewById(R.id.textView)
        }
    }

    // Create new views (invoked by the layout manager)
    override fun onCreateViewHolder(viewGroup: ViewGroup, viewType: Int): ViewHolder {
        // Create a new view.
        val v = LayoutInflater.from(viewGroup.context)
                .inflate(R.layout.text_row_item, viewGroup, false)

        return ViewHolder(v)
    }

    // Replace the contents of a view (invoked by the layout manager)
    override fun onBindViewHolder(viewHolder: ViewHolder, position: Int) {
        Log.d(TAG, "Element $position set.")

        // Get element from your dataset at this position and replace the contents of the view
        // with that element
        viewHolder.textView.text = dataSet[position]
    }

    // Return the size of your dataset (invoked by the layout manager)
    override fun getItemCount() = dataSet.size

    companion object {
        private val TAG = "CustomAdapter"
    }
}

The layout manager calls the adapter's onCreateViewHolder() method. That method needs to construct a RecyclerView.ViewHolder and set the view it uses to display its contents. The type of the ViewHolder must match the type declared in the Adapter class signature. Typically, it would set the view by inflating an XML layout file. Because the view holder is not yet assigned to any particular data, the method does not actually set the view's contents.

The layout manager then binds the view holder to its data. It does this by calling the adapter's onBindViewHolder() method, and passing the view holder's position in the RecyclerView. The onBindViewHolder() method needs to fetch the appropriate data, and use it to fill in the view holder's layout. For example, if the RecyclerView is displaying a list of names, the method might find the appropriate name in the list, and fill in the view holder's TextView widget.

If the list needs an update, call a notification method on the RecyclerView.Adapter object, such as notifyItemChanged(). The layout manager then rebinds any affected view holders, allowing their data to be updated.