Building Simple Chat Client with Parse

The following tutorial explains how to build a very simple chat application in Android using Parse backend-as-a-service.

Note: This chat application is by no means a fully-featured or production ready chat app. This tutorial is an illustration of how to quickly build an app using Parse.

1. Setup Parse server

We can deploy our own Parse data store and push notifications systems to Back4App leveraging the server open-sourced by Parse. Parse is built on top of the MongoDB database which can be added to Heroku using MongoLab.

To follow this guide we need to setup our own Parse server. Once the Parse server is configured, we can initialize Parse within our Android app pointing the client to our self-hosted URL. After that, the tutorial works the same as before.

You will need to save application id & client key that you can find in Back4App Dashboard. Look for "App Settings" section in the right nav bar of Back4App Dashboard, then open Security&Keys.

2. Setup Parse client

Let's setup Parse into a brand new Android app following the steps below.

  • Generate a new android project in your IDE (minSDK 18) and call it SimpleChat.

    • Name the first (main) activity: ChatActivity.
    • Add this to the allprojects section of your root build.gradle::
    allprojects {
        repositories {
            google()
            jcenter()
            maven { url "https://jitpack.io" }
        }
    }
    • Add the following to your app/build.gradle:
    dependencies {
      implementation 'com.github.parse-community.Parse-SDK-Android:parse:1.24.1'
      implementation 'com.squareup.okhttp3:logging-interceptor:3.8.1' // for logging API calls to LogCat
    }
    • Make sure you have added these lines before the <application> tag in your AndroidManifest.xml.
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
  • Create an application class called ChatApplication which extends from android.app.Application

    public class ChatApplication extends Application {
        @Override
        public void onCreate() {
            super.onCreate();
    
           // Use for monitoring Parse network traffic        
            OkHttpClient.Builder builder = new OkHttpClient.Builder();
            HttpLoggingInterceptor httpLoggingInterceptor = new HttpLoggingInterceptor();
            // Can be Level.BASIC, Level.HEADERS, or Level.BODY
            httpLoggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
            // any network interceptors must be added with the Configuration Builder given this syntax
            builder.networkInterceptors().add(httpLoggingInterceptor);
    
            // set applicationId and server based on the values in the Back4App settings.
            Parse.initialize(new Parse.Configuration.Builder(this)
                 .applicationId("YOUR_APPLICATION_ID") // Application ID from Back4App Dashboard
                 .clientKey("YOUR_CLIENT_KEY") // Client Key from Back4App Dashboard
                 .clientBuilder(builder)
                 .server("https://parseapi.back4app.com").build());
        }
    }
  • Add the qualified android:name of your Application subclass to the <application> tag in your AndroidManifest.xml.

    <application
      android:name=".ChatApplication"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      ...>
          <activity 
             ... 
          />
    />

WARNING: Be sure to add the application name above after creating the custom Application class or the following code won't work!!

3. Design Messages Layout

Let's create an XML layout which allows us to post messages by typing into a text field. Open your layout file activity_chat.xml, add an EditText and a Button to compose and send text messages.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:background="@android:color/white"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- Chat messages view will go here -->

    <RelativeLayout
        android:id="@+id/rlSend"
        android:layout_alignParentBottom="true"
        android:layout_width="match_parent"
        android:paddingTop="5dp"
        android:paddingBottom="10dp"
        android:paddingLeft="0dp"
        android:paddingRight="0dp"
        android:layout_height="wrap_content" >
        <EditText
            android:id="@+id/etMessage"
            android:layout_toLeftOf="@+id/btSend"
            android:layout_alignBottom="@+id/btSend"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="top"
            android:hint="@string/message_hint"
            android:inputType="textShortMessage"
            android:imeOptions="actionSend"
            />
        <ImageButton
            android:id="@+id/btSend"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:paddingRight="10dp"
            android:layout_alignParentRight="true"
            android:contentDescription="@string/send"
            android:src="@drawable/ic_baseline_send_24"
            android:textSize="18sp" />
    </RelativeLayout>
</RelativeLayout>

The imeOptions attribute is used to control the icon in the Soft Keyboard. The gravity attribute will position the button at the center vertically AND on the right horizontally.

Notice that we are using ImageButton. It allows setting a background image using android:src attribute. Now, let's add a new icon that represents a send message. Select File -> New -> Vector asset. In the "Asset Studio" dialog select "Asset Type: Clip Art". Then click on a "Clip Art" button and search for "Send" asset. You can keep defaults for the rest of the settings or experiment changing colors and outline style.

Another thing to notice is a new attribute android:contentDescription. This attribute refers to a string that we will define in a second. Although ImageButton doesn't display text, this text is used for accessibility.

  • Add the following values to res-->values-->strings.xml file.
<string name="message_hint">Say anything</string>
<string name="send">Send</string>

4. Login With Anonymous Parse user

For the sake of simplicity, we will use an anonymous user to log into our simple chat app. An anonymous user is a user that can be created without a username and password but still has all of the same capabilities as any other ParseUser. After logging out, an anonymous user is abandoned, and its data is no longer accessible.

Open your main activity class (ChatActivity.java) and make the following changes:

public class ChatActivity extends AppCompatActivity {
    static final String TAG = ChatActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat);
        // User login
        if (ParseUser.getCurrentUser() != null) { // start with existing user
            startWithCurrentUser();
        } else { // If not logged in, login as a new anonymous user
            login();
        }
    }
    
    // Get the userId from the cached currentUser object
    void startWithCurrentUser() {
        // TODO:
    }
    
    // Create an anonymous user using ParseAnonymousUtils and set sUserId 
    void login() {
        ParseAnonymousUtils.logIn(new LogInCallback() {
	    @Override
	    public void done(ParseUser user, ParseException e) {
                if (e != null) {
                    Log.e(TAG, "Anonymous login failed: ", e);
                } else {
                    startWithCurrentUser();
                }
            }
       });		
    }
}

5. Save Messages

Next, we will setup UI views in ChatActivity.java. On click of 'Send' button, we'll save the message object to Parse. This is done by constructing a new ParseObject and then calling saveInBackground() to persist data to the database.

public class ChatActivity extends AppCompatActivity {
...
    static final String USER_ID_KEY = "userId";
    static final String BODY_KEY = "body";

    EditText etMessage;
    ImageButton btSend;

...

    // Get the userId from the cached currentUser object
    void startWithCurrentUser() {
        setupMessagePosting();
    }

    // Setup button event handler which posts the entered message to Parse
    void setupMessagePosting() {
        // Find the text field and button
        etMessage = (EditText) findViewById(R.id.etMessage);
        btSend = (ImageButton) findViewById(R.id.btSend);
        
        // When send button is clicked, create message object on Parse
        btSend.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                String data = etMessage.getText().toString();
                ParseObject message = ParseObject.create("Message");
                message.put(USER_ID_KEY, ParseUser.getCurrentUser().getObjectId());
                message.put(BODY_KEY, data);
                message.saveInBackground(new SaveCallback() {
                    @Override
                    public void done(ParseException e) {
                        if(e == null) {
                    	    Toast.makeText(ChatActivity.this, "Successfully created message on Parse",
                             Toast.LENGTH_SHORT).show();
                        } else {
                            Log.e(TAG, "Failed to save message", e);
                        }
                    }
                });
                etMessage.setText(null);
            }
        });
    }
}

6. Verify Save

At this point, run your application and try to send a text to Parse. If the save was successful, you should see 'Successfully created message on Parse' toast on your screen.

WARNING If you're using self-deployed Back4App backend you might need to create a new class to save messages. Navigate to your project's Dashboard --> Core --> Database Broswer and click "Create a class". Select "Message" as a name for your class and add 2 columns:

  • userId of type String
  • body of type String

Try sending message again from the app. You can then check if the data was saved by verifying whether the objects were created in Back4App Dshboard. Navigate to your project's Dashboard --> Core --> Database Broswer --> Messages to see if the message appears there.

Refer testing Parse deployment guide for more info.

7. Add RecyclerView to Chat Layout

Now that we have verified that messages are successfully being saved to your parse database, lets go ahead and build the UI to retrieve these messages. Open your layout file activity_chat.xml and add a RecyclerView to display the text messages from parse.

First, add the RecyclerView as a dependency in your app/build.gradle:

dependencies {
    ...
    implementation 'androidx.recyclerview:recyclerview:1.0.0'
}

Next, add your RecyclerView to the layout (scroll down to see code snippet for ConstraintLayout):

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
  android:background="@android:color/white"
  android:layout_width="match_parent"
  android:layout_height="match_parent">
    <androidx.recyclerview.widget.RecyclerView
      android:id="@+id/rvChat"
      android:transcriptMode="alwaysScroll"
      android:layout_alignParentTop="true"
      android:layout_alignParentLeft="true"
      android:layout_alignParentRight="true"
      android:layout_above="@+id/rlSend"
      android:layout_width="wrap_content"
      android:layout_height="match_parent" />
    <RelativeLayout 
      android:id="@+id/rlSend"
      android:layout_alignParentBottom="true"
      android:layout_width="match_parent"
      android:paddingTop="5dp"
      android:paddingBottom="10dp"
      android:paddingLeft="0dp"
      android:paddingRight="0dp"
      android:layout_height="wrap_content" >
      <EditText
          android:id="@+id/etMessage"
          android:layout_toLeftOf="@+id/btSend"
          android:layout_alignBottom="@+id/btSend"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:gravity="top"
          android:hint="@string/message_hint"
          android:inputType="textShortMessage"
          android:imeOptions="actionSend"
        />
        <ImageButton
            android:id="@+id/btSend"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:paddingRight="10dp"
            android:layout_alignParentRight="true"
            android:contentDescription="@string/send"
            android:src="@drawable/ic_baseline_send_24"
            android:textSize="18sp" />
    </RelativeLayout>
</RelativeLayout>

ConstraintLayout code will look like this:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <EditText
        android:id="@+id/etMessage"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:hint="@string/message_hint"
        android:imeOptions="actionSend"
        android:inputType="textShortMessage"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/btSend"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/rvChat" />

    <ImageButton
        android:id="@+id/btSend"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:paddingRight="10dp"
        android:layout_alignParentRight="true"
        android:contentDescription="@string/send"
        android:src="@drawable/ic_baseline_send_24"
        android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/etMessage"
        app:layout_constraintTop_toTopOf="@+id/etMessage" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rvChat"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        app:layout_constraintBottom_toTopOf="@+id/etMessage"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

7.1 Add layouts for incoming and outgoing messages

In this lab we will learn how to use adapter to create different views for incoming and outgoing messages. We will be showing the outgoing messages with our gravatar on the right and all the incoming messages with gravatars and sender names on the left. You can read more about creating gravatars here.

Now we need to create two layout file to represent each chat type of message - incoming & outgoing - in the list view. Put this into res/layout/message_incoming.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:paddingVertical="10dp"
    android:paddingLeft="15dp"
    android:paddingRight="60dp"
    android:clipToPadding="false">

    <TextView
        android:id="@+id/tvName"
        android:layout_marginLeft="15dp"
        android:layout_toRightOf="@+id/ivProfileOther"
        android:layout_alignTop="@+id/ivProfileOther"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingBottom="4dp"
        android:text="Johny Lindsey" />

    <ImageView
        android:id="@+id/ivProfileOther"
        android:layout_alignParentLeft="true"
        android:contentDescription="@string/profile_other"
        android:layout_width="64dp"
        android:layout_height="64dp"
        android:src="@mipmap/ic_launcher" />
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tvBody"
        android:layout_below="@+id/tvName"
        android:layout_alignLeft="@+id/tvName"
        android:background="@drawable/message_incoming"
        android:paddingVertical="12dp"
        android:paddingHorizontal="16dp"
        android:elevation="2dp"
        android:textSize="18dp"
        android:text="Someone else's message" />
</RelativeLayout>

For outgoing (our) messages create another layout file messages_outgoing:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:clipToPadding="false"
    android:paddingVertical="10dp"
    android:paddingLeft="60dp"
    android:paddingRight="15dp">

    <TextView
        android:id="@+id/tvBody"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginRight="8dp"
        android:layout_toLeftOf="@+id/ivProfileMe"
        android:background="@drawable/message_outgoing"
        android:elevation="2dp"
        android:padding="8dp"
        android:text="Your outgoing message here"
        android:textColor="@android:color/white"
        android:textSize="18dp" />

    <ImageView
        android:id="@+id/ivProfileMe"
        android:layout_width="64dp"
        android:layout_height="64dp"
        android:layout_alignParentRight="true"
        android:contentDescription="@string/profile_me"
        android:src="@mipmap/ic_launcher" />

</RelativeLayout>

Add the following values to res-->values-->strings.xml file:

<string name="profile_me">My Profile Pic</string>
<string name="profile_other">Other profile pic</string>

As we learned before, those labels can be picked up by accessibility framework in Android and pronounced to a user who relies on TalkBack

7.2 Creating chat "bubble" backgrounds

In order to re-create popular chat "bubble" UI we need to define proper backgrounds. We referred to them in the section 7.1 as @drawable/message_outgoing and @drawable/message_incoming. In res --> drawable folder create two files:

<!-- message_outgoing.xml -->
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="@color/colorPrimary" />
    <corners android:topRightRadius="5dp" android:radius="15dp" />
</shape>

and

<!-- message_incoming.xml -->
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="#fff" />
    <corners android:topLeftRadius="5dp" android:radius="15dp" />
</shape>

8. Create Model Class

Now let's create a Message.java class which will extend from ParseObject. This model class will provide message data for the RecyclerView and will be used to retrieve and save messages to Parse.

@ParseClassName("Message")
public class Message extends ParseObject {
    public static final String USER_ID_KEY = "userId";
    public static final String BODY_KEY = "body";

    public String getUserId() {
        return getString(USER_ID_KEY);
    }

    public String getBody() {
        return getString(BODY_KEY);
    }

    public void setUserId(String userId) {
        put(USER_ID_KEY, userId);
    }

    public void setBody(String body) {
        put(BODY_KEY, body);
    }
}

We also need to make sure to register this class with Parse before we call Parse.initialize within the ChatApplication.java file:

public class ChatApplication extends Application {
    // ...
    @Override
    public void onCreate() {
        super.onCreate();
        // ...
        ParseObject.registerSubclass(Message.class);

        // Use for monitoring Parse OkHttp trafic
        // Can be Level.BASIC, Level.HEADERS, or Level.BODY
        // See http://square.github.io/okhttp/3.x/logging-interceptor/ to see the options.
        OkHttpClient.Builder builder = new OkHttpClient.Builder();
        HttpLoggingInterceptor httpLoggingInterceptor = new HttpLoggingInterceptor();
        // ...

    }
    // ...
}

Finally, we refactor ChatActivity and rename the references to the model keys

...
void setupMessagePosting() {
        // Find the text field and button
        etMessage = (EditText) findViewById(R.id.etMessage);
        btSend = (ImageButton) findViewById(R.id.btSend);
        // When send button is clicked, create message object on Parse
        btSend.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String data = etMessage.getText().toString();

                // Delete the following three lines:
                //ParseObject message = ParseObject.create("Message");
                //message.put(Message.USER_ID_KEY, ParseUser.getCurrentUser().getObjectId());
                //message.put(Message.BODY_KEY, data);

                /*** START OF CHANGE **/

                // Using new `Message` Parse-backed model now
                Message message = new Message();
                message.setBody(data);
                message.setUserId(ParseUser.getCurrentUser().getObjectId());

                /*** END OF CHANGE **/

                message.saveInBackground(new SaveCallback() {
                    @Override
                    public void done(ParseException e) {
                        if(e == null) {
                    	    Toast.makeText(ChatActivity.this, "Successfully created message on Parse",
                             Toast.LENGTH_SHORT).show();
                        } else {
                            Log.e(TAG, "Failed to save message", e);
                        }
                    }
                });
                etMessage.setText(null);
            }
        });
    }
...

With our model defined with Parse and properly registered, we can now use this model to store and retrieve message data.

9. Create Custom List Adapter

Create a class named ChatAdapter.java with below code. This is a custom list adapter class which provides data to list view. In other words it renders the message_incoming.xml (or message_outgoing.xml) in list by pre-filling appropriate information. We'll be using the open source Glide library to load profile images.

First, add dependency for this library to the app/build.gradle file:

...
dependencies {
    implementation 'com.github.bumptech.glide:glide:4.11.0'
}

9.1 Create a basic adapter

We start by creating a very basic ChatAdapter that extends RecyclerView.Adapter. We will initialize the adapter instance by passing context, userId and the list of our chat messages:

public class ChatAdapter extends RecyclerView.Adapter<ChatAdapter.MessageViewHolder> {

    private List<Message> mMessages;
    private Context mContext;
    private String mUserId;

    public ChatAdapter(Context context, String userId, List<Message> messages) {
        mMessages = messages;
        this.mUserId = userId;
        mContext = context;
    }

    @Override
    public int getItemCount() {
        return mMessages.size();
    }

    @Override
    public int getItemViewType(int position) {
        // TODO: implement method
    }

    @Override
    public MessageViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        // TODO: implement method
    }

    @Override
    public void onBindViewHolder(MessageViewHolder holder, int position) {
        // TODO: implement method
    }

}

We will keep implementing the adapter in the next couple chapters.

9.2 Define view types

Now it's time to define the view types and implement the code that will allow adapter to decide which view type to use for every message in our chat.

First, let's define two integer constants types MESSAGE_INCOMING and MESSAGE_OUTGOING. Their values can be choosen at random as long as they are not the same 😅

Second, we will implement getItemViewType(int position) that will return view type (incoming or outgoing) based on the message position. Our adapter should look like this:


public class ChatAdapter extends RecyclerView.Adapter<ChatAdapter.MessageViewHolder> {
...
    private static final int MESSAGE_OUTGOING = 123;
    private static final int MESSAGE_INCOMING = 321;

    @Override
    public int getItemViewType(int position) {
        if (isMe(position)) {
            return MESSAGE_OUTGOING;
        } else {
            return MESSAGE_INCOMING;
        }
    }
}

The function isMe() is a little helper function that can be implemented like this:

  private boolean isMe(int position) {
      Message message = mMessages.get(position);
      return message.getUserId() != null && message.getUserId().equals(mUserId);
  }

9.3 Creating custom ViewHolders for view types

Every message type is represented by its own view that we defined in XML layouts. Each of those views can be assigned its own ViewHolder type. If you need a refresher on ViewHolder patern, see this guide.

Let's begin by defining a common ViewHolder base class - MessageViewHolder. This class will be the lowest common denominator between Incoming and Outgoing messages. You can define those classes inside ChatAdapter class or create a separate file for ViewHolders.

public class ChatAdapter extends RecyclerView.Adapter<ChatAdapter.MessageViewHolder> {
...
   public abstract class MessageViewHolder extends RecyclerView.ViewHolder {

        public MessageViewHolder(@NonNull View itemView) {
            super(itemView);
        }

        abstract void bindMessage(Message message);
    }
}

In this example we define the class as abstract meaning it can't have any instances. Let's define actual implementations for incoming and outgoing message view holders:

...
   public abstract class MessageViewHolder extends RecyclerView.ViewHolder {

        public MessageViewHolder(@NonNull View itemView) {
            super(itemView);
        }

        abstract void bindMessage(Message message);
    }

    public class IncomingMessageViewHolder extends MessageViewHolder {
        ImageView imageOther;
        TextView body;
        TextView name;

        public IncomingMessageViewHolder(View itemView) {
            super(itemView);
            imageOther = (ImageView)itemView.findViewById(R.id.ivProfileOther);
            body = (TextView)itemView.findViewById(R.id.tvBody);
            name = (TextView)itemView.findViewById(R.id.tvName);
        }

        @Override
        public void bindMessage(Message message) {
            // TODO: implement later
        }
    }

    public class OutgoingMessageViewHolder extends MessageViewHolder {
        ImageView imageMe;
        TextView body;

        public OutgoingMessageViewHolder(View itemView) {
            super(itemView);
            imageMe = (ImageView)itemView.findViewById(R.id.ivProfileMe);
            body = (TextView)itemView.findViewById(R.id.tvBody);
        }

        @Override
        public void bindMessage(Message message) {
            // TODO: implement later
        }
    }

As you can see those ViewHolders have different view components assigned to them. This is because we previously decided to have different view layouts to easily distinguish the messages in our chat.

Next, we need to assign correct view holders based on a view type:

public class ChatAdapter extends RecyclerView.Adapter<ChatAdapter.MessageViewHolder> {
...
    @Override
    public MessageViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        LayoutInflater inflater = LayoutInflater.from(context);

        if (viewType == MESSAGE_INCOMING) {
            View contactView = inflater.inflate(R.layout.message_incoming, parent, false);
            return new IncomingMessageViewHolder(contactView);
        } else if (viewType == MESSAGE_OUTGOING) {
            View contactView = inflater.inflate(R.layout.message_outgoing, parent, false);
            return new OutgoingMessageViewHolder(contactView);
        } else {
            throw new IllegalArgumentException("Unknown view type");
        }
    }
}

In the example above we create new views from xml layout and assign them to corresponding view holders. In case if the view type is different from the ones we defined we will throw an exception. This is a good choice that follows "fail fast" programming principle. Since the "Unknown view type" is an unlikely scenario it would be better to crash application notifying a developer that something goes wrong.

9.4 Binding data to ViewHolders

In this final part of the adapter setup we will bind data from individual messages to corresponding ViewHolders. Let's start by defining how each ViewHolder displays their message:

    public class IncomingMessageViewHolder extends MessageViewHolder {
...
        @Override
        public void bindMessage(Message message) {
            Glide.with(mContext)
                    .load(getProfileUrl(message.getUserId())) 
                    .circleCrop() // create an effect of a round profile picture
                    .into(imageOther);
            body.setText(message.getBody());
            name.setText(message.getUserId()); // in addition to message show user ID
        }
    }

    public class OutgoingMessageViewHolder extends MessageViewHolder {
...

        @Override
        public void bindMessage(Message message) {
            Glide.with(mContext)
                    .load(getProfileUrl(message.getUserId()))
                    .circleCrop() // create an effect of a round profile picture
                    .into(imageMe);
            body.setText(message.getBody());
        }
    }

    // Create a gravatar image based on the hash value obtained from userId
    private static String getProfileUrl(final String userId) {
        String hex = "";
        try {
            final MessageDigest digest = MessageDigest.getInstance("MD5");
            final byte[] hash = digest.digest(userId.getBytes());
            final BigInteger bigInt = new BigInteger(hash);
            hex = bigInt.abs().toString(16);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "https://www.gravatar.com/avatar/" + hex + "?d=identicon";
    }

In the code above we use Glide library to load gravatars from a given URL. If you need a refresher on Glide see Displaying Images with the Glide Library. The method getProfileUrl() is responsible for decoding user ID and creating an image URL that can be passed into the Glide library.

Finally, we should tell ChatAdapter how (and when) to bind different message types to different view types:

public class ChatAdapter extends RecyclerView.Adapter<ChatAdapter.MessageViewHolder> {
...
    @Override
    public void onBindViewHolder(MessageViewHolder holder, int position) {
        Message message = mMessages.get(position);
        holder.bindMessage(message);
    }

}

Here you can see an example of one of the object-oriented programming principles - polymorphism - in action. Since we defined the MessageViewHolder as a parent class for both types of the message the runtime will decide what is the right bindMessage() call for a given ViewHolder.

10. Bind Adapter to the RecyclerView

Next, we will setup the ReyclerView and bind our custom adapter to this ReyclerView within the ChatActivity.java source file:

public class ChatActivity extends AppCompatActivity {
...

    RecyclerView rvChat;    
    ArrayList<Message> mMessages;
    ChatAdapter mAdapter;
    // Keep track of initial load to scroll to the bottom of the ListView
    boolean mFirstLoad;
	
    // Setup message field and posting
    void setupMessagePosting() {
        // Find the text field and button
        etMessage = (EditText) findViewById(R.id.etMessage);
        btSend = (Button) findViewById(R.id.btSend);
        rvChat = (RecyclerView) findViewById(R.id.rvChat);
        mMessages = new ArrayList<>();
        mFirstLoad = true;
        final String userId = ParseUser.getCurrentUser().getObjectId();
        mAdapter = new ChatAdapter(ChatActivity.this, userId, mMessages);
        rvChat.setAdapter(mAdapter);

        // associate the LayoutManager with the RecylcerView
        final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(ChatActivity.this);
        rvChat.setLayoutManager(linearLayoutManager);

        // When send button is clicked, create message object on Parse
        btSend.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String data = etMessage.getText().toString();
                //ParseObject message = ParseObject.create("Message");
                //message.put(Message.USER_ID_KEY, userId);
                //message.put(Message.BODY_KEY, data);
                // Using new `Message` Parse-backed model now
                Message message = new Message();
                message.setBody(data);
                message.setUserId(ParseUser.getCurrentUser().getObjectId());
                message.saveInBackground(new SaveCallback() {
                    @Override
                    public void done(ParseException e) {
                        Toast.makeText(ChatActivity.this, "Successfully created message on Parse",
                                Toast.LENGTH_SHORT).show();
                        refreshMessages();
                    }
                });
                etMessage.setText(null);
            }
        });
    }

    // Query messages from Parse so we can load them into the chat adapter
    void refreshMessages() {
        // TODO:
    }
    ...
}

11. Receive Messages

Now we can fetch last 50 messages from parse and bind them to the RecyclerView with the use of our custom messages adapter within ChatActivity.java:

public class ChatActivity extends AppCompatActivity {
...
    static final int MAX_CHAT_MESSAGES_TO_SHOW = 50;
...
    // Query messages from Parse so we can load them into the chat adapter
    void refreshMessages() {
        // Construct query to execute
        ParseQuery<Message> query = ParseQuery.getQuery(Message.class);
        // Configure limit and sort order
        query.setLimit(MAX_CHAT_MESSAGES_TO_SHOW);

        // get the latest 50 messages, order will show up newest to oldest of this group
        query.orderByDescending("createdAt");
        // Execute query to fetch all messages from Parse asynchronously
        // This is equivalent to a SELECT query with SQL
        query.findInBackground(new FindCallback<Message>() {
            public void done(List<Message> messages, ParseException e) {
                if (e == null) {
                    mMessages.clear();
                    mMessages.addAll(messages);
                    mAdapter.notifyDataSetChanged(); // update adapter
                    // Scroll to the bottom of the list on initial load
                    if (mFirstLoad) {
                        rvChat.scrollToPosition(0);
                        mFirstLoad = false;
                    }
                } else {
                    Log.e("message", "Error Loading Messages" + e);
                }
            }
        });
    }
}

If you get to this step, you will display the newest posts ordered from newest to oldest. You can reverse the order without necessarily doing a linear sort by setting setReverseLayout to be true.

public class ChatActivity extends AppCompatActivity {

    // Get the items in the reverse order:
    void setupMessagePosting() {
        // ...
        final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(ChatActivity.this);
        linearLayoutManager.setReverseLayout(true);
        // ...
    }
    // ...
}

Now, we should be able to see the messages in the list after posting but we won't yet see them update on load or as new messages are created on other clients.

12. Refreshing Messages

Finally, let's periodically refresh the RecyclerView with latest messages using a handler. The handler will call a runnable to fetch new messages every 3 second. This is a primitive "polling" rather than the more efficient "push" technique for refreshing new messages - but will work for the purposes of this simple project.

WARNING It's important to remember, that polling often leads to redundancy, e.g. making many unnecessary requests when there was no change in data. In addition to that, frequent requests are costly due to increased battery drain and cost of cell data traffic. We will look at a couple techniques to prevent unnecessary polling when application is inactive.

...

// Create a handler which can run code periodically
static final long POLL_INTERVAL = TimeUnit.SECONDS.toMillis(3); 
Handler myHandler = new android.os.Handler();
Runnable mRefreshMessagesRunnable = new Runnable() {
    @Override
    public void run() {
       refreshMessages();
       myHandler.postDelayed(this, POLL_INTERVAL);
    }
};

...

    @Override
    protected void onResume() {
        super.onResume();

        // Only start checking for new messages when the app becomes active in foreground
        myHandler.postDelayed(mRefreshMessagesRunnable, POLL_INTERVAL);
    }

    @Override
    protected void onPause() {
        // Stop background task from refreshing messages, to avoid unnecessary traffic & battery drain
        myHandler.removeCallbacksAndMessages(null);
        super.onPause();
    }
}

The methods onResume() and onPause() are sort of mirror lifecycle callbacks. First is getting called when the Activity is ready to be resumed and about to be displayed to the user. onPause() is the exact opposite and gets called when a current Activity is about to go into background.

It's important to only start polling when onResume() is getting called and ensuring we stop listening for any callbacks as soon as activity becomes invisible. However, in production chat application you might want to run a backgroun service that will be periodically checking for messages and displaying Message notifications to a user.

See the repeating periodic tasks guide to learn more about the handler.

13. Live Queries

Alternatively, the Heroku server can be configured properly to listen to the Message object for changes (see this example). We need to add a liveQuery field in our Parse server installation. See this guide for more context.

var api = new ParseServer({
  liveQuery: { classNames: ["Message"]},
});

We can then use Parse Live Queries to listen for new messages. We can disable the use of the postDelayed() runnable that we created in the earlier step:

// myHandler.postDelayed(mRefreshMessagesRunnable, POLL_INTERVAL);

First, make sure to add the Parse LiveQuery dependency to your app/build.gradle config:

allprojects {
	repositories {
		maven { url "https://jitpack.io" }
	}
}

dependencies {
      implementation 'com.github.parse-community:ParseLiveQuery-Android:1.1.0' // for Parse Live Queries
}

Next, we will configure to listen for any newly created Message object:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // ...

    // Parse.initialize(...) should happen first, preferably in a different file such as your MyApplication.java

    // Load existing messages to begin with
    refreshMessages();

    // Make sure the Parse server is setup to configured for live queries
    // URL for server is determined by Parse.initialize() call.
    ParseLiveQueryClient parseLiveQueryClient = ParseLiveQueryClient.Factory.getClient();

    ParseQuery<Message> parseQuery = ParseQuery.getQuery(Message.class);
    // This query can even be more granular (i.e. only refresh if the entry was added by some other user)
    // parseQuery.whereNotEqualTo(USER_ID_KEY, ParseUser.getCurrentUser().getObjectId());

    // Connect to Parse server
    SubscriptionHandling<Message> subscriptionHandling = parseLiveQueryClient.subscribe(parseQuery);

    // Listen for CREATE events
    subscriptionHandling.handleEvent(SubscriptionHandling.Event.CREATE, new
        SubscriptionHandling.HandleEventCallback<Message>() {
        @Override
        public void onEvent(ParseQuery<Message> query, Message object) {
            mMessages.add(0, object);

            // RecyclerView updates need to be run on the UI thread
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    mAdapter.notifyDataSetChanged();
                    rvChat.scrollToPosition(0);
                }
            });
        }
    });
}

14. Final AndroidManifest.xml

The final manifest for this chat application looks like:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codepath.android.simplechat">

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

    <application
        android:name="com.codepath.android.simplechat.ChatApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name="com.codepath.android.simplechat.ChatActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

15. Final Output

Run your project and test it out with your pair partner. Below is the final output.

Chat App|250

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