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Display Collections - Java SDK

On this page

  • Install Adapters
  • Example Models
  • Display Collections in a ListView
  • Display Collections in a RecyclerView

Android apps often populate the UI using RecyclerView or ListView components. Realm offers adapters to display realm object collections. These collections implement the OrderedRealmCollections interface. RealmResults and RealmList are examples of these adaptors. With these adapters, UI components update when your app changes Realm objects.

Install Adapters

Add these dependencies to your application level build.gradle file:

dependencies {
   implementation 'io.realm:android-adapters:4.0.0'
   implementation 'androidx.recyclerview:recyclerview:1.1.0'
}

Realm hosts these adapters on the JCenter artifact repository. To use jcenter in your Android app, add it to your project-level build.gradle file:

buildscript {
    repositories {
        jcenter()
    }
}
allprojects {
    repositories {
        jcenter()
    }
}

Tip

See also:

Source code: realm/realm-android-adapters on GitHub.

Example Models

The examples on this page use a Realm object named Item. This class contains a string named "name" and an identifier number named "id":

import io.realm.RealmObject;
public class Item extends RealmObject {
    int id;
    String name;
    public Item() {}
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}
import io.realm.RealmObject
open class Item(var id: Int = 0,
                var name: String? = null): RealmObject()

Display Collections in a ListView

Display Realm objects in a ListView by extending RealmBaseAdapter. The adapter uses the ListAdapter interface. Implementation works like any ListAdapter. This provides support for automatically-updating Realm objects.

Subclass RealmBaseAdapter to display Item objects in a ListView:

import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.ListAdapter;
import android.widget.TextView;
import com.mongodb.realm.examples.model.java.Item;
import io.realm.OrderedRealmCollection;
import io.realm.RealmBaseAdapter;
class ExampleListAdapter extends RealmBaseAdapter<Item> implements ListAdapter {
    String TAG = "REALM_LIST_ADAPTER";
    ExampleListAdapter(OrderedRealmCollection<Item> realmResults) {
        super(realmResults);
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        if (convertView == null) {
            Log.i(TAG, "Creating view holder");
            // create a top-level layout for our item views
            LinearLayout layout = new LinearLayout(parent.getContext());
            layout.setLayoutParams(
                    new ViewGroup.LayoutParams(
                            ViewGroup.LayoutParams.MATCH_PARENT,
                            ViewGroup.LayoutParams.MATCH_PARENT));
            // create a text view to display item names
            TextView titleView = new TextView(parent.getContext());
            titleView.setLayoutParams(
                    new ViewGroup.LayoutParams(
                            ViewGroup.LayoutParams.MATCH_PARENT,
                            ViewGroup.LayoutParams.MATCH_PARENT));
            // attach the text view to the item view layout
            layout.addView(titleView);
            convertView = layout;
            viewHolder = new ViewHolder(titleView);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        // as long as we
        if (adapterData != null) {
            final Item item = adapterData.get(position);
            viewHolder.title.setText(item.getName());
            Log.i(TAG, "Populated view holder with data: " + item.getName());
        } else {
            Log.e(TAG, "No data in adapter! Failed to populate view holder.");
        }
        return convertView;
    }
    private static class ViewHolder {
        TextView title;
        public ViewHolder(TextView textView) {
            title = textView;
        }
    }
}

To display list data in an activity, instantiate a ListView. Then, attach an ExampleListAdapter:

// instantiate a ListView programmatically
ListView listView = new ListView(activity.getApplicationContext());
listView.setLayoutParams(
        new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.MATCH_PARENT));
// create an adapter with a RealmResults collection
// and attach it to the ListView
ExampleListAdapter adapter =
        new ExampleListAdapter(
                realm.where(Item.class).findAll());
listView.setAdapter(adapter);
ViewGroup.LayoutParams layoutParams =
        new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.MATCH_PARENT);
activity.addContentView(listView, layoutParams);
import android.util.Log
import android.view.View
import android.view.ViewGroup
import android.widget.LinearLayout
import android.widget.ListAdapter
import android.widget.TextView
import com.mongodb.realm.examples.model.kotlin.Item
import io.realm.OrderedRealmCollection
import io.realm.RealmBaseAdapter
internal class ExampleListAdapter(realmResults: OrderedRealmCollection<Item?>?) :
    RealmBaseAdapter<Item?>(realmResults), ListAdapter {
    var TAG = "REALM_LIST_ADAPTER"
    override fun getView(position: Int,
                         convertView: View?,
                         parent: ViewGroup): View {
        var convertView = convertView
        val viewHolder: ViewHolder
        if (convertView == null) {
            Log.i(TAG, "Creating view holder")
            // create a top-level layout for our item views
            val layout = LinearLayout(parent.context)
            layout.layoutParams = ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.MATCH_PARENT
            )
            // create a text view to display item names
            val titleView = TextView(parent.context)
            titleView.layoutParams = ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.MATCH_PARENT
            )
            // attach the text view to the item view layout
            layout.addView(titleView)
            convertView = layout
            viewHolder = ViewHolder(titleView)
            convertView.tag = viewHolder
        } else {
            viewHolder = convertView.tag as ViewHolder
        }
        // as long as we
        if (adapterData != null) {
            val item = adapterData!![position]!!
            viewHolder.title.text = item.name
            Log.i(TAG, "Populated view holder with data: ${item.name}")
        } else {
            Log.e(TAG, "No data in adapter! Failed to populate view holder.")
        }
        return convertView
    }
    private class ViewHolder(var title: TextView)
}

To display list data in an activity, instantiate a ListView. Then, attach an ExampleListAdapter:

// instantiate a ListView programmatically
val listView = ListView(activity!!.applicationContext)
listView.layoutParams = ViewGroup.LayoutParams(
    ViewGroup.LayoutParams.MATCH_PARENT,
    ViewGroup.LayoutParams.MATCH_PARENT
)
// create an adapter with a RealmResults collection
// and attach it to the ListView
val adapter = ExampleListAdapter(realm.where(Item::class.java).findAll())
listView.adapter = adapter
val layoutParams = ViewGroup.LayoutParams(
    ViewGroup.LayoutParams.MATCH_PARENT,
    ViewGroup.LayoutParams.MATCH_PARENT
)
activity!!.addContentView(listView, layoutParams)

Display Collections in a RecyclerView

Display Realm objects in a RecyclerView by extending RealmRecyclerViewAdapter. The adapter extends RecyclerView.Adapter. Implementation works like any RecyclerView adapter. This provides support for automatically-updating Realm objects.

Subclass RealmRecyclerViewAdapter to display Item objects in a RecyclerView:

import android.util.Log;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.recyclerview.widget.RecyclerView;
import com.mongodb.realm.examples.model.java.Item;
import io.realm.OrderedRealmCollection;
import io.realm.RealmRecyclerViewAdapter;
/*
 * ExampleRecyclerViewAdapter: extends the Realm-provided
 * RealmRecyclerViewAdapter to provide data
 * for a RecyclerView to display
 * Realm objects on screen to a user.
 */
class ExampleRecyclerViewAdapter
        extends RealmRecyclerViewAdapter<Item,
        ExampleRecyclerViewAdapter.ExampleViewHolder> {
    String TAG = "REALM_RECYCLER_ADAPTER";
    ExampleRecyclerViewAdapter(OrderedRealmCollection<Item> data) {
        super(data, true);
        Log.i(TAG, "Created RealmRecyclerViewAdapter for "
                + getData().size() + " items.");
    }
    @Override
    public ExampleViewHolder onCreateViewHolder(ViewGroup parent,
                                                int viewType) {
        Log.i(TAG, "Creating view holder");
        TextView textView = new TextView(parent.getContext());
        textView.setLayoutParams(
                new ViewGroup.LayoutParams(
                        ViewGroup.LayoutParams.MATCH_PARENT,
                        ViewGroup.LayoutParams.WRAP_CONTENT));
        return new ExampleViewHolder(textView);
    }
    @Override
    public void onBindViewHolder(ExampleViewHolder holder,
                                 int position) {
        final Item obj = getItem(position);
        Log.i(TAG, "Binding view holder: " + obj.getName());
        holder.data = obj;
        holder.title.setText(obj.getName());
    }
    @Override
    public long getItemId(int index) {
        return getItem(index).getId();
    }
    class ExampleViewHolder extends RecyclerView.ViewHolder {
        TextView title;
        public Item data;
        ExampleViewHolder(TextView view) {
            super(view);
            title = view;
        }
    }
}

To display list data in an activity, instantiate a RecyclerView. Then, attach an ExampleRecyclerViewAdapter:

// instantiate a RecyclerView programmatically
RecyclerView recyclerView =
        new RecyclerView(activity.getApplicationContext());
recyclerView.setLayoutManager(
        new LinearLayoutManager(activity.getApplicationContext()));
recyclerView.setHasFixedSize(true);
recyclerView.addItemDecoration(new DividerItemDecoration(
        activity.getApplicationContext(),
        DividerItemDecoration.VERTICAL));
// create an adapter with a RealmResults collection
// and attach it to the RecyclerView
ExampleRecyclerViewAdapter adapter =
        new ExampleRecyclerViewAdapter(
                realm.where(Item.class).findAll());
recyclerView.setAdapter(adapter);
ViewGroup.LayoutParams layoutParams =
        new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.MATCH_PARENT);
activity.addContentView(recyclerView, layoutParams);
import android.util.Log
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import com.mongodb.realm.examples.model.kotlin.Item
import io.realm.OrderedRealmCollection
import io.realm.RealmRecyclerViewAdapter
/*
 * ExampleRecyclerViewAdapter: extends the Realm-provided
 * RealmRecyclerViewAdapter to provide data
 * for a RecyclerView to display
 * Realm objects on screen to a user.
 */
internal class ExampleRecyclerViewAdapter(data: OrderedRealmCollection<Item?>?) :
    RealmRecyclerViewAdapter<Item?,
            ExampleRecyclerViewAdapter.ExampleViewHolder?>(data, true) {
    var TAG = "REALM_RECYCLER_ADAPTER"
    override fun onCreateViewHolder(parent: ViewGroup,
                                    viewType: Int): ExampleViewHolder {
        Log.i(TAG, "Creating view holder")
        val textView = TextView(parent.context)
        textView.layoutParams = ViewGroup.LayoutParams(
            ViewGroup.LayoutParams.MATCH_PARENT,
            ViewGroup.LayoutParams.WRAP_CONTENT
        )
        return ExampleViewHolder(textView)
    }
    override fun onBindViewHolder(holder: ExampleViewHolder, position: Int) {
        val obj = getItem(position)
        Log.i(TAG, "Binding view holder: ${obj!!.name}")
        holder.data = obj
        holder.title.text = obj.name
    }
    override fun getItemId(index: Int): Long {
        return getItem(index)!!.id.toLong()
    }
    internal inner class ExampleViewHolder(var title: TextView)
        : RecyclerView.ViewHolder(title) {
        var data: Item? = null
    }
    init {
        Log.i(TAG,
            "Created RealmRecyclerViewAdapter for ${getData()!!.size} items.")
    }
}

To display list data in an activity, instantiate a RecyclerView. Then, attach an ExampleRecyclerViewAdapter:

// instantiate a RecyclerView programmatically
val recyclerView = RecyclerView(activity!!.applicationContext)
recyclerView.layoutManager =
    LinearLayoutManager(activity!!.applicationContext)
recyclerView.setHasFixedSize(true)
recyclerView.addItemDecoration(
    DividerItemDecoration(activity!!.applicationContext,
        DividerItemDecoration.VERTICAL))
// create an adapter with a RealmResults collection
// and attach it to the RecyclerView
val adapter = ExampleRecyclerViewAdapter(realm.where(Item::class.java).findAll())
recyclerView.adapter = adapter
val layoutParams = ViewGroup.LayoutParams(
    ViewGroup.LayoutParams.MATCH_PARENT,
    ViewGroup.LayoutParams.MATCH_PARENT
)
activity!!.addContentView(recyclerView, layoutParams)

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