Adding Tweet Streaming Feature in World Mood Tracker loklak App

The World Mood Tracker was added to loklak apps with the feature to display aggregated data from the emotion classifier of loklak server. The next step in the app was adding the feature to display the stream of Tweets from a country as they are discovered by loklak. With the addition of stream servlet in loklak, it was possible to utilise it in this app.

In this blog post, I will be discussing the steps taken while adding to introduce this feature in World Mood Tracker app.

Props for WorldMap component

The WorldMap component holds the view for the map displayed in the app. This is where API calls to classifier endpoint are made and results are displayed on the map. In order to display tweets on clicking a country, we need to define react props so that methods from higher level components can be called.

In order to enable props, we need to change the constructor for the component –

export default class WorldMap extends React.Component {
    constructor(props) {
        super(props);
        ...
    }
    ...
}

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We can now pass the method from parent component to enable streaming and other components can close the stream by using props in them –

export default class WorldMoodTracker extends React.Component {
    ...
    showStream(countryName, countryCode) {
        /* Do something to enable streaming component */
        ...
    }
 
    render() {
        return (
             ...
                <WorldMap showStream={this.showStream}/>
             ...
        )
    }
}

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Defining Actions on Clicking Country Map

As mentioned in an earlier blog post, World Mood Tracker uses Datamaps to visualize data on a map. In order to trigger a piece of code on clicking a country, we can use the “done” method of the Datamaps instance. This is where we use the props passed earlier –

done: function(datamap) {
    datamap.svg.selectAll('.datamaps-subunit').on('click', function (geography) {
        props.showStream(geography.properties.name, reverseCountryCode(geography.id));
    })
}

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The name and ID for the country will be used to display name and make API call to stream endpoint respectively.

The StreamOverlay Component

The StreamOverlay components hold all the utilities to display the stream of Tweets from loklak. This component is used from its parent components whose state holds info about displaying this component –

export default class WorldMoodTracker extends React.Component {
    ...
    getStreamOverlay() {
        if (this.state.enabled) {
            return (<StreamOverlay
                show={true} channel={this.state.channel}
                country={this.state.country} onClose={this.onOverlayClose}/>);
        }
    }

    render() {
        return (
            ...
                {this.getStreamOverlay()}
            ...
        )
    }
}

[SOURCE]

The corresponding props passed are used to render the component and connect to the stream from loklak server.

Creating Overlay Modal

On clicking the map, an overlay is shown. To display this overlay, react-overlays is used. The Modal component offered by the packages provides a very simple interface to define the design and interface of the component, including style, onclose hook, etc.

import {Modal} from 'react-overlays';

<Modal aria-labelledby='modal-label'
    style={modalStyle}
    backdropStyle={backdropStyle}
    show={true}
    onHide={this.close}>
    <div style={dialogStyle()}>
        ...
    </div>
</Modal>

[SOURCE]

It must be noted that modalStyle and backdropStyle are React style objects.

Dialog Style

The dialog style is defined to provide some space at the top, clicking where, the overlay is closed. To do this, vertical height units are used –

const dialogStyle = function () {
    return {
        position: 'absolute',
        width: '100%',
        top: '5vh',
        height: '95vh',
        padding: 20
        ...
    };
};

[SOURCE]

Connecting to loklak Tweet Stream

loklak sends Server Sent Events to clients connected to it. To utilise this stream, we can use the natively supported EventSource object. Event stream is started with the render method of the StreamOverlay component –

render () {
    this.startEventSource(this.props.channel);
    ...
}

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This channel is used to connect to twitter/country/<country-ID> channel on the stream and then this can be passed to EventStream constructor. On receiving a message, a list of Tweets is appended and later rendered in the view –

startEventSource(country) {
    let channel = 'twitter%2Fcountry%2F' + country;
    if (this.eventSource) {
        return;
    }
    this.eventSource = new EventSource(host + '/api/stream.json?channel=' + channel);
    this.eventSource.onmessage = (event) => {
        let json = JSON.parse(event.data);
        this.state.tweets.push(json);
        if (this.state.tweets.length > 250) {
            this.state.tweets.shift();
        }
        this.setState(this.state);
    };
}

[SOURCE]

The size of the list is restricted to 250 here, so when a newer Tweet comes in, the oldest one is chopped off. And thanks to fast DOM actions in React, the rendering doesn’t take much time.

Rendering Tweets

The Tweets are displayed as simple cards on which user can click to open it on Twitter in a new tab. It contains basic information about the Tweet – screen name and Tweet text. Images are not rendered as it would make no sense to load them when Tweets are coming at a high rate.

function getTweetHtml(json) {
    return (
        <div style={{padding: '5px', borderRadius: '3px', border: '1px solid black', margin: '10px'}}>
            <a href={json.link} target="_blank">
            <div style={{marginBottom: '5px'}}>
                <b>@{json['screen_name']}</b>
            </div>
            <div style={{overflowX: 'hidden'}}>{json['text']}</div>
            </a>
        </div>
    )
}

[SOURCE]

They are rendered using a simple map in the render method of StreamOverlay component –

<div className={styles.container} style={{'height': '100%', 'overflowY': 'auto',
    'overflowX': 'hidden', maxWidth: '100%'}}>
    {this.state.tweets.reverse().map(getTweetHtml)}
</div>

[SOURCE]

Closing Overlay

With the previous setup in place, we can now see Tweets from the loklak backend as they arrive. But the problem is that we will still be connected to the stream when we click-close the modal. Also, we would need to close the overlay from the parent component in order to stop rendering it.

We can use the onclose method for the Modal here –

close() {
    if (this.eventSource) {
        this.eventSource.close();
        this.eventSource = null;
    }
    this.props.onClose();
}

[SOURCE]

Here, props.onClose() disables rendering of StreamOverlay in the parent component.

Conclusion

In this blog post, I explained how the flow of props are used in the World Mood Tracker app to turn on and off the streaming in the overlay defined using react-overlays. This feature shows a basic setup for using the newly introduced stream API in loklak.

The motivation of such application was taken from emojitracker by mroth as mentioned in fossasia/labs.fossasia.org#136. The changes were proposed in fossasia/apps.loklak.org#315 by @singhpratyush (me).

The app can be accessed live at https://singhpratyush.github.io/world-mood-tracker/index.html.

Resources

Create an App Widget for Bookmarked Sessions for the Open Event Android App

What is an app widget?

App Widgets are miniature application views that can be embedded in other applications (such as the Home screen) and receive periodic updates. These views are referred to as Widgets in the user interface, and you can publish one with an App Widget provider. – (Android Documentation).

Android widget is an important functionality that any app can take advantage of. It could be used to show important dates, things that the user personalizes on the app etc. In the context of the Open Event Android App, it was necessary to create a bookmark widget for the Android phones so that the user could see his bookmarks on the homescreen itself and need not open the app for the same. In the open event android app, the widget was already created but it needed bug fixes and UI enhancements due to migration to the Realm database migration. Therefore, my majority of work circled around that.

Implementation

Declare the app widget in the manifest. All the updates in the application would be received by the class which extends the AppWidgetProvider if it needs to be reflected in the widget.

<receiver
   android:name=".widget.BookmarkWidgetProvider"
   android:enabled="true"
   android:label="Bookmarks">
   <intent-filter>
       <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
       <action android:name="${applicationId}.ACTION_DATA_UPDATED" />
       <action android:name="${applicationId}.UPDATE_MY_WIDGET" />
   </intent-filter>
   <meta-data
       android:name="android.appwidget.provider"
       android:resource="@xml/widget_info" />
</receiver>

 

Create a layout for the widget that is to be displayed on the homescreen. Remember to use only the views defined in the documentation. After the creation of the layout, create a custom widget updater which will broadcast the data from the app to the receiver to update the widget.

public class WidgetUpdater {
   public  static  void updateWidget(Context context){
       int widgetIds[] = AppWidgetManager.getInstance(context.getApplicationContext()).getAppWidgetIds(new ComponentName(context.getApplicationContext(), BookmarkWidgetProvider.class));
       BookmarkWidgetProvider bookmarkWidgetProvider = new BookmarkWidgetProvider();
       bookmarkWidgetProvider.onUpdate(context.getApplicationContext(), AppWidgetManager.getInstance(context.getApplicationContext()),widgetIds);
       context.sendBroadcast(new Intent(BookmarkWidgetProvider.ACTION_UPDATE));
   }
}

 

Next, create a custom RemoteViewService to update the views in the widget. The reason this is required is because the app widget does not operate in the usual lifecycle of the app. And therefore a remote service is required which acts as the remote adapter to connect to the remote views. In your class, override the onGetViewFactory() method and create a new remoteViewsFactory object to get the the data from the app on updation of the bookmark list. To populate the remote views, override the getViewsAt() method.

public class BookmarkWidgetRemoteViewsService extends RemoteViewsService {

@Override
public RemoteViewsFactory onGetViewFactory(Intent intent) {

return new RemoteViewsFactory() {
   private MatrixCursor data = null;

   @Override
   public void onCreate() {
       //Called when your factory is first constructed.
   }

   @Override
   public void onDataSetChanged() {
       }

   @Override
   public RemoteViews getViewAt(int position) {
       } 
   }
}

 

Finally, create a custom AppWidgetProvider which parses the relevant fields out of the intent and updates the UI. It acts like a broadcast receiver, hence all the updates by the widgetUpdater is received here.

public class BookmarkWidgetProvider extends AppWidgetProvider {

   public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
	  RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.bookmark_widget);
             setRemoteAdapter(context, views);

   }

   @Override
   public void onReceive(@NonNull Context context, @NonNull Intent intent) {
       super.onReceive(context, intent);
   }

   private void setRemoteAdapter(Context context, @NonNull final RemoteViews views) {
       views.setRemoteAdapter(R.id.widget_list,
               new Intent(context, BookmarkWidgetRemoteViewsService.class));
   }

}

 

Conclusion

For any event based apps, it is crucial that it regularly provide updates to its users and therefore app widget forms an integral part of that whole experience.

References

 

 

Responsive Image Overlay

Image overlay is a very common concept in front-end development. It is easy to implement but difficult when we deal it with different screen sizes, where we need to cover the image with the overlay each time the screen size is changed. I have gone through various blog posts when I need to implement the same for Open-event webapp and researched a solution that works for all screen sizes without any media query.

1234

How to add an overlay to an image ?

If we need four images in a single row nearly 300*300px.  The code below shows the markup.

image-holder : The parent class to take the image and overlay inside it.

background-image: This class takes image source.

responsive-overlay: This is the key point to make it responsive. Responsive-overlay contains a class hover-state to add overlay absolutely and a class social-links.

social-links: It adds content to hover-state.

 

<div class="image-holder">
  <img class="background-image" alt="" src="">
   <div class="responsive-overlay">
     <div class="hover-state text-center preserve3d">
       <div class="social-links vertical-align">

       </div>
     </div>
   </div>
 </div>

The styling is written with SASS in .scss file as shown below.

//overlayimage and backgroundshade can be set in config.scss

 .image-holder {
   position: relative;
   overflow: hidden;
   margin-bottom: 12px;

   .background-image {
     height: 300px;
     width: 300px;
     display: block;
     margin: 0 auto;
     background-color: $background-shade;
    }
 
   .responsive-overlay {
     @include responsiveoverlay;

    .preserve3d {
       height: 300px;
      }

    .hover-state {
     @include hoverstate;
     height: 300px;
     width: 300px;
    }

  @mixin responsiveoverlay {
     height: 100%;
     position: absolute;
     top: 0;
     width: 100%;
}

   @mixin hoverstate {
     background: $overlayimage;
     display: block;
     height: 300px;
     left: 0;
     margin: 0 auto;
     opacity: 0;
     position: relative;
     top: 0;
     -moz-transition: all 0.3s ease-out;
     -webkit-transition: all 0.3s ease-out;
     transition: all 0.3s ease-out;
     width: 300px;
     z-index: 2;
   }

This code will work for responsiveness as well. The main catch here is the responsive-overlay class which is made 100% in width but set to position absolute. The images which are 300 * 300 px in size will take an overlay of the same size because of hover-state class. Instead, if we adjust sizes of images in small screens the above code will adjust overlay on the image automatically.

Like, on tablets we can have an overlay like this.

345

And on mobile screen output is like that :

23

Conclusion

Responsiveness is easy if we follow correct concepts. Here, the concepts of absolute and relative positioning in CSS have done the magic. Now we can play by adding different contents and effect on hover following the same basics.