Debugging Using Stetho in Open Event Android

The Open Event Android project helps event organizers to generator Apps (apk format) for their events/conferences by providing api end point or zip generated using Open Event server. In this android app data is fetched from the internet using network calls to the Open Event server and the data of the event is stored in a database. It is difficult to debug an app with so many network calls and database connectivity. A way to approach this is using  Stetho which is very helpful tool for debugging an app which deals with network calls and database.  

Stetho is Facebook’s open source project works as debug bridge for android applications which gives powerful Chrome Developers Tools for debugging android applications using Chrome desktop browser.

What can you do using stetho ?

  • Analyze network traffic
  • Inspect elements(layouts/views)  
  • View SQLite database in table format
  • Run queries on SQLite database
  • View shared preference and edit it
  • Manipulate android app from command line

Setup

1. Add Gradle dependency

To add stetho in your app add ‘com.facebook.stetho:stetho:1.5.0’ dependency in your app  module’s build.gradle file. This dependency is strictly required.

dependencies{
    compile 'com.facebook.stetho:stetho:1.5.0'
}

For network inspection add one of the following dependency according to which you will be using

'com.facebook.stetho:stetho-okhttp:1.5.0'
'com.facebook.stetho:stetho-okhttp3:1.5.0'
'com.facebook.stetho:stetho-urlconnection:1.5.0'

2. Initialize stetho

Initialize stetho in class MyApplication which extends Application class by overriding  onCreate() method. Make sure you have added MyAppication in manifest.

public class MyApplication extends Application {
    public void onCreate() {
        super.onCreate()
        Stetho.initializeWithDefaults(this);
    }
}

Stetho.initializeWithDefaults(this) initializes stetho with defaults configuration(without network inspection and more). It will be able to debug database.

Manifest file

<Application   android:name=”.MyApplication    …   />

For enabling network inspection add StethoInterceptor  in OkHttpClient

new OkHttpClient.Builder()
    .addNetworkInterceptor(new StethoInterceptor())
    .build();

Using Chrome Developer Tools

1. Open Inspect window

Run stetho initialized app on device or emulator then start Google chrome and type chrome://inspect. You will see you device with your app’s package name. Click on “inspect”2. Network Inspection

Go to Network tab. It will show all network calls. With almost all info like url(path), method, returned status code, returned data type, size, time taken etc.

You can also see preview of image and preview, response of returned json data by clicking on Name.

3. SQLite Database

Go to “Resources”  tab and select “Web SQL”. You will see database file(.db). By clicking on database file you will see all tables in that database file. And by clicking on table name you will see data in row-column format for that table.

4. Run queries on SQLite database

Same as above go to “Resources”  tab and select “Web SQL”. You will see database file(.db). By clicking on database file you will see console on right side, where you can run queries on SQLite database. Example,

SELECT * FROM tracks ;

5. Shared Preferences Inspection

Go to “Resources”  tab and select “Local Storage”. You will show all files that your app used to save key-value pairs in shared preference and by clicking on file you will see all key-value pairs.

6. Element(View/Layout) Inspection

Go to “Elements” tab. You will see top layout/view in view hierarchy. By clicking it you will see child layout/view of that layout/view. On hover on layout/view you view will be inspected in your device/emulator.

 

In this blog the most important have been put forward, but there are still  some nice stuff available,like:

  • An integration with JavaScript Console : Enables JavaScript code execution that can interact with the application
  • Dumpapp  : It allows an integration higher than the Developer Tools, enabling the development of custom plugins.

By now, you must have realized that stetho can significantly improve your debugging experience. To learn more about stetho, refer to

Recyclerview in Open Event Android: A great upgradation to ListView

Recently, I was fixing a trivial bug in the Open Event Android app, an interesting thing caught my attention. Most of the lists in the app where actually not implemented using the traditional ListView, but instead used something called RecyclerView. The beautiful transitions that make this app the beauty it is, is due to the amazing and easy to code Recycler Views used in it.

A screen shot showcasing the simplicity of the FOSSASIA Open event android app.

 

List View is one among the various views that Android provides. In a nutshell, it is literally a group of generic views in Android. Why then use an entire new and more complex view, if all that it offers is a number of views displayed together? Well, it certainly has certain add-ons to the most generic set of views like Image and TextViews in Android.

I encourage you to think about what different could the ListView be as compared to multiple declarations of TextView. The thing with multiple declarations of a Text or Image View is that they aren’t “scrollable”, that is, if you want numerous Views in a single activity, without List View, you will have to fit them on one screen, else make another activity. So, if you want a scrollable view with same basic view items, List View is the way to go about it in Android.

The next question that may arise is:

How does a Listview work?

Google defines Adapters as “a bridge between an AdapterView and the underlying data for that view”. List Views use Adapters that retrieve data from Arrays, Lists and other data structures and queries, plugs them into our List View and thus, creates a beautiful looking List in no time. In Spite of all this, List View certainly lags in various fields that deal with performance, memory and compactness issues. As a great improvement Recycler View was introduced.

Using Recyclerview you are not restricted to vertical scrollable views. It has the ability to provide horizontal, vertical, grid and staggered layouts among others, with the help of different layout managers:-

recyclerView.setLayoutManager(new StaggeredGridLayoutManager(2,StaggeredGridLayoutManager.VERTICAL));
recyclerView.setLayoutManager(new LinearLayoutManager(RecyclerView_Activity.this,LinearLayoutManager.HORIZONTAL, false));

RecyclerView.ItemDecoration class allows us to add special drawings to our view. Thus, we can add dividers, borders and much more using this class.

public class DividerItemDecoration extends RecyclerView.ItemDecoration {
 
     private Drawable mDivider;
 
     public DividerItemDecoration(Drawable divider) {
         mDivider = divider;
     }

Adding animation used to be a devil of a task in Listview days, however with the release of Recyclerview, it has become a lot more easy. RecyclerView.ItemAnimator class helps in animating items while the adapters are being changed.

Next, we have something related to the performance:-

In a List View, you might have come across the term, ‘Viewholder’, but if you haven’t, that’s okay too. However, in Recyclerview, using View Holders have been made mandatory and for a good reason. The class goes by the name RecyclerView.ViewHolder.

What exactly are View Holders?
The clean dividers and minimal design in the Recyclerview makes up for a subtle UI.

In a broader sense, it is used to provide information about the identity of an itemView and it’s position within a Recyclerview. Without View Holders we have an overhead of calling the function findViewById() for every item in our Recyclerview! This upgradation from the typical findViewById() to View Holders awards us with better and more smooth scrolling through the list.

How does Recyclerview work?

List View is an ancestor to Recyclerview. Recyclerview has everything that List View offers to us (except for a few things like setchoicemode(), which I might take up in my upcoming blog posts), and much more.

A great achievement that Android achieved through Recyclerview has been it’s ability to “recycle” views on the way. In laymen terms, if you scroll through a Recyclerview, the views that go away from the screen during scrolling are the same views that come into the screen. The only difference is that the data in the views leaving the screen is changed to the data of the views entering your screen and so they are presented as new views. In this way, a Recyclerview helps saving memory for sure as compared to List Views.

There are still a lot of other things to learn about Recycler and List Views and you find more resources here.

 

Implementing Google Maps in Open Event ember Front-end

In the deployment of the Open Event Front-end on eventyay.com we want to show an event’s location on a map using Google Maps. Since Eventyay.com requires Google map to be used at several web pages, we can use Google map as an ember component for reusability.

How did we do it? The following walks you through the entire process.

The first step is to: Install g-map addon-

  • ember g-map, which is an addon, is available on ember add-on library which can be found at emberobserver.com. So first import that library using ember cli command
ember install ember-g-map
  • This command adds an ember-g-map module in our node_modules and also updated package.json file of our app now our ember-g-map modules contains the following directories. The following three are required to be highlighted that serves our purpose-
  • Addon/ – this directory contains all the implementation logic which acts as a prototype for the g-map component
  • App/- this directory basically exports a copy of g-map from our Addon/ directory to the web page where it is required. The export includes the logic implement inside the Addon/ directory which can later be imported by the parent app for use.Package.json – this file holds various metadata relevant to the ember-g-map

Generate Component-

  • The next step is to generate a component event-map (we can name our component anything we want but be sure to add a hyphen between the name). The component can be generated with the help of the following command of ember cli-
ember g component public/event-map

This will add three files in our app –

event-map.js located at app/component/public/event-map.js

event-map.hbs located at app/template/component/public/event-map.hbs

event-map-test.js located at tests/integration/component/public/event-map-test.js

Define Component-

Now let us use these files to add a google map component in our app-

  • First of all, we have to tell index.hbs about our new component that we are going to add. So we add our component {{public/event-map}} in our index.hbs file which is located at app/templates/public/index.hbs And we fetch latitude, longitude and location name from model and store in the event object and pass it to our component so that this information is available in the component.
<div class="location">
<h1 id="getting-here">{{t 'Getting Here'}}</h1>
 {{public/event-map event=model.event}}
</div>
  • The event-map.js file will be used to add ui grid class to assign a class to the div of the component. This will alleviate the redundancy regarding the creation of an extra div to enclose the component and then giving it the ui grid class.
import Ember from 'ember';
 
const { Component } = Ember;
 
export default Component.extend({
 classNames: ['ui', 'stackable', 'grid']
});
  • In our event-map.hbs we have with us the latitude, longitude, and locationName available and we are good to use our g-map addon. So in our event-map.hbs we can directly add g-map and g-map-marker but make sure that we pass lat and lang attributes to it. We can use custom options like backgroundColor, draggable etc. but here we have used street view and gestureHandling. gestureHandling is set as “cooperative” so that for smaller screen device,  zooming is possible only with two fingers so that scrolling would become easy.
<div class="eight wide column event-map">
 {{#g-map lat=event.latitude lng=event.longitude 
 zoom=12 gestureHandling='cooperative' 
 streetView='StreetViewPanorama' as |context|}}
 {{g-map-marker context lat=event.latitude lng=event.longitude}}
 {{/g-map}}
</div>
<div class="eight wide column address">
 <h1>{{t 'Address'}}</h1>
 <p>{{event.locationName}}</p>
</div>
  • Next we have to decide the size of aur google map canvas on which our map is to be displayed. We define the size of our canvas in the public-event.scss file which is located under styles/pages/public-event-scss.
.event-map > .g-map {
 height: 100%;
 width: 100%;
}
 
.event-map > .g-map > .g-map-canvas {
 height: 300px;
}
  • Lastly, we have to modify our event-map-test.js file. Here we perform integration test for our component. We create a dummy object with latitude, longitude, and locationName in it and pass it to our component and then check if it renders correctly or not.
import { test } from 'ember-qunit';

import moduleForComponent from 'open-event-frontend/tests/helpers/component-helper';

import hbs from 'htmlbars-inline-precompile';

moduleForComponent('public/event-map', 'Integration | Component | public/event map');

let event = Object.create({ latitude: 37.7833, longitude: -122.4167, locationName: 'Sample event location address' });

test('it renders', function(assert) {

  this.set('event', event);

  this.render(hbs `{{public/event-map event=event}}`);

  assert.equal(this.$('.address p').text(), 'Sample event location address');

});

Now use ember s command in our ember cli and visit localhost:4200

Then open a event at the end we see our Google map integrated.

Use ember test –server command to check if all our tests (integration, acceptance, etc.) are passed.

 

Find out more at – ember-g-map

PayPal Express Checkout in Python

As per the PayPal documentation …

Express Checkout is a fast, easy way for buyers to pay with PayPal. Express Checkout eliminates one of the major causes of checkout abandonment by giving buyers all the transaction details at once, including order details, shipping options, insurance choices, and tax totals.

The basic steps for using express checkout to receive one-time payments are:

  1. Getting the PayPal API credentials.
  2. Making a request to the API with the transaction details to get a token
  3. Using the token to send the users to the PayPal payment page
  4. Capturing the payment and charging the user after the user completes the payment at PayPal.

We will be using PayPal’s Classic NVP (Name-value pair) API for implementing this.

Getting PayPal API Credentials

To begin with, we’ll need API Credentials.
We’ll be using the Signature API credentials which consists of

  • API Username
  • API Password
  • Signature

To obtain these, you can follow the steps at Creating and managing NVP/SOAP API credentials – PayPal Developer.

You’ll be getting two sets of credentials. Sandbox and Live. We’ll just stick to the Sandbox for now.

Now, we need sandbox test accounts for making and receiving payments. Head over to Creating Sandbox Test Accounts – PayPal Developer and create two sandbox test accounts. One would be the facilitator and one would be the buyer.

PayPal NVP Servers

All the API actions will take place by making a request to the PayPal server. PayPal has 4 different NVP servers for 4 different purposes.

  1. https://api-3t.sandbox.paypal.com/nvp – Sandbox “testing” server for use with API signature credentials.
  2. https://api-3t.paypal.com/nvp– PayPal “live” production server for use with API signature credentials.
  3. https://api.sandbox.paypal.com/nvp – Sandbox “testing” server for use with API certificate credentials.
  4. https://api.paypal.com/nvp – PayPal “live” production server for use with API certificate credentials.

We’ll be using the Sandbox “testing” server for use with API signature credentials.

Creating a transaction and obtaining the token

To create a transaction, we’ll need to make a request with all the transaction details. We can use Python requests library to easily make the requests. All requests are POST.

We’ll be calling the SetExpressCheckout method of the NVP API to obtain the token.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'SetExpressCheckout',
    'VERSION': 93,
    'PAYMENTREQUEST_0_PAYMENTACTION': 'SALE',
    'PAYMENTREQUEST_0_AMT': 100,
    'PAYMENTREQUEST_0_CURRENCYCODE': 'USD',
    'RETURNURL': 'http://localhost:5000/paypal/return/',
    'CANCELURL': 'http://localhost:5000/paypal/cancel/'
}
response = requests.post('https://api-3t.sandbox.paypal.com/nvp', data=data)  
token = dict(urlparse.parse_qsl(response.text))['TOKEN']

Here,

  • USER represents your Sandbox API Username.
  • PWD represents your Sanbox API Password.
  • SIGNATURE represents your Sandbox Signature.
  • SUBJECT represents the facilitator’s email ID.
  • PAYMENTREQUEST_0_AMT is the total transaction amount.
  • PAYMENTREQUEST_0_CURRENCYCODE is the 3 digit ISO 4217 Currency code.
  • RETURNURL is where the user will be sent to after the transaction
  • CANCELURL is where the user will be sent to if he/she cancels the transaction.

A URL-Encoded, Name-value pair response would be obtained. We can decode that into a dict by using Python’s urlparse modules.

From the response, we’re extracting the TOKEN which we will use to generate the payment URL for the user.

This token has to be retained since we’ll be using it in further steps of the process.

Redirecting the user to PayPal for Approval

With the token we obtained, we can form the payment URL.

https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_express-checkout&token=<TOKEN>

We’ll have to send the user to that URL. Once the user completes the transaction at PayPal, he/she will be returned to the RETURNURL where we’ll further process the transaction.

Obtaining approved payment details and capturing the payment

Once the user completes the transaction and gets redirected back to RETURNURL, we’ll have to obtain the confirmed payment details from PayPal. For that we can again use the token ID that we obtained before.

We’ll now be making a request to the GetExpressCheckoutDetails method of the API.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'GetExpressCheckoutDetails',
    'VERSION': 93,
    'TOKEN': TOKEN
}

response = requests.post('https://api-3t.sandbox.paypal.com/nvp', data=data)  
result = dict(urlparse.parse_qsl(response.text))  
payerID = result['PAYERID']

A URL-Encoded, Name-value pair response would be obtained. We can decode that into a dict by using Python’s urlparse modules.

This will provide us with information about the transaction such as transaction time, transaction amount, charges, transaction mode, etc.

But, we’re more interested in the PAYERID which we’ll need to capture/collect the payment. The money is not transferred to the facilitators account until it is captured/collected. So, be sure to collect it.

To collect it, we’ll be making another request to the DoExpressCheckoutPaymentmethod of the API using the token and the PAYERID.

import requests  
import urlparse

data = {  
    'USER': credentials['USER'],
    'PWD': credentials['PWD'],
    'SIGNATURE': credentials['SIGNATURE'],
    'SUBJECT': credentials['FACILITATOR_EMAIL'],
    'METHOD': 'DoExpressCheckoutPayment',
    'VERSION': 93,
    'TOKEN': TOKEN,
    'PAYERID': payerID,
    'PAYMENTREQUEST_0_PAYMENTACTION': 'SALE',
    'PAYMENTREQUEST_0_AMT': 100,
    'PAYMENTREQUEST_0_CURRENCYCODE': 'USD',
}

response = requests.post('https://api-3t.sandbox.paypal.com/nvp', data=data)  
result = dict(urlparse.parse_qsl(response.text))  
status = result['ACK']

All the details have to be the same as the ones provided while obtaining the token. Once we make the request, we’ll again get a URL-Encoded, Name-value pair response. We can decode that into a dict by using Python’s urlparsemodules.

From the response, ACK (Acknowledgement status) will provide us with the status of the payment.

  • Success — A successful operation.
  • SuccessWithWarning — A successful operation; however, there are messages returned in the response that you should examine.
  • Failure — The operation failed; the response also contains one or more error messages explaining the failure.
  • FailureWithWarning — The operation failed and there are messages returned in the response that you should examine.

And, we have completed the PayPal transaction flow for Express Checkout. These are just the basics and might miss a few stuff. I suggest you go through the following links too for a better understanding of everything:

For Reference:
  1. PayPal Name-Value Pair API Basics – PayPal Developer
  2. How to Create One-Time Payments Using Express Checkout – PayPal Developer

Creating a Widget for your Android App

Having a widget for your app, not only helps it to stand out among its alternatives but also provides user information on the go without having to open the app. Keeping this thought in mind, I decided to make a widget for my GSoC project. Let’s go through the steps involved.

Step 1:

Creating a new widget from Android Studio.

Open up your project for which you need a widget and navigate to the project’s Java source. Create a new sub-package there named widget. Right click on the newly created sub-package and select the New->Widget option from there.

new_widget

Follow the instructions on the next screen.

screenshot-area-2016-07-30-002554
Most of the fields here are pretty much self explanatory. After doing this and running the app in your device, you will be able to see a widget for your app in the widget picker.
Screenshot_20160730-003515_01

 

Just kidding, this was the easy part, off to more harder things now!

Step 2:

Populating the widget with data.

Now, there can be 2 broad type of widgets Information Widgets and Collection Widgets.

Information widgets are simple widgets that are used to display an information that changes with time, for example Weather Widget or a Clock Widget.

Whereas, collection widgets are widgets which display a collection of data, for example the GMail widget is a collection widget.
These are relatively complex and harder than the Information Widgets.

In this post, we will focus on making a Collection Widget.

For Collection widgets, we need two layout files, one for the widget and one for each item in the widget collection.

Go ahead and create the two layout files. The wizard automatically generates the widget_layout.xml for you, you just need to edit it up.

stock_layout.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <LinearLayout
        android:layout_width="match_parent"
        android:id="@+id/widget_toolbar"
        android:layout_height="?android:attr/actionBarSize"
        android:background="@color/colorPrimary">

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:src="@drawable/stock_up"
            android:contentDescription="@string/stock_widget" />

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:src="@drawable/stock_down"
            android:contentDescription="@string/stock_widget" />

        <TextView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginStart="32dp"
            android:gravity="center_vertical"
            android:text="@string/your_stocks"
            android:textAppearance="@android:style/TextAppearance.DeviceDefault.Widget.ActionBar.Title"
            android:layout_marginLeft="32dp" />
    </LinearLayout>

    <ListView
        android:id="@+id/widget_listView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/backGround"></ListView>

</LinearLayout>
list_item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="72dp"
    android:gravity="center_vertical"
    android:orientation="horizontal"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    >
  <TextView
      android:id="@+id/stock_symbol"
      style="@style/StockSymbolTextStyle"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:gravity="start|center_vertical"
      tools:text="List Item"
      />
</LinearLayout>

Next up, having a look at the modified files, we can see that the Widget creation wizard added some stuff into out AndroidManifest.xml and created a new java file.

Upon taking a closer look at the manifest, we can see that the widget’s java class has been registered as a <receiver/>

Next, opening up the NewAppWidget.java, we will see that it extends AppWidgetProvider and some methods are already overridden for you.

Time to edit up this file to reference to the layouts we have just created.

import android.annotation.TargetApi;
import android.app.PendingIntent;
import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.Context;
import android.content.Intent;
import android.os.Build;
import android.support.annotation.NonNull;
import android.widget.RemoteViews;

/**
 * Implementation of App Widget functionality.
 */
public class StockWidgetProvider extends AppWidgetProvider {

    private static void updateAppWidget(Context context, AppWidgetManager appWidgetManager,
                                        int appWidgetId) {
        // Construct the RemoteViews object which defines the view of out widget
        RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.widget_layout);
        // Instruct the widget manager to update the widget
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
            setRemoteAdapter(context, views);
        } else {
            setRemoteAdapterV11(context, views);
        }
        /** PendingIntent to launch the MainActivity when the widget was clicked **/
        Intent launchMain = new Intent(context, MainActivity.class);
        PendingIntent pendingMainIntent = PendingIntent.getActivity(context, 0, launchMain, 0);
        views.setOnClickPendingIntent(R.id.widget, pendingMainIntent);
        appWidgetManager.notifyAppWidgetViewDataChanged(appWidgetId,R.id.widget_listView);
        appWidgetManager.updateAppWidget(appWidgetId, views);
    }

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
        // There may be multiple widgets active, so update all of them
        for (int appWidgetId : appWidgetIds) {
            updateAppWidget(context, appWidgetManager, appWidgetId);
        }

        super.onUpdate(context, appWidgetManager, appWidgetIds);
    }

    @Override
    public void onEnabled(Context context) {
        // Enter relevant functionality for when the first widget is created
    }

    @Override
    public void onDisabled(Context context) {
        // Enter relevant functionality for when the last widget is disabled
    }

  /** Set the Adapter for out widget **/

    @TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
    private static void setRemoteAdapter(Context context, @NonNull final RemoteViews views) {
        views.setRemoteAdapter(R.id.widget_listView,
                new Intent(context, StockWidgetService.class));
    }

    
    /** Deprecated method, don't create this if you are not planning to support devices below 4.0 **/
    @SuppressWarnings("deprecation")
    private static void setRemoteAdapterV11(Context context, @NonNull final RemoteViews views) {
        views.setRemoteAdapter(0, R.id.widget_listView,
                new Intent(context, StockWidgetService.class));
    }

}

Now, create a WidgetDataProvider which will provide us with data to be displayed inside the widget.

You can use a static data for now (like a prefilled ArrayList, but make sure that this data should be dynamic for making the widget meaningful)

import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.os.Binder;
import android.widget.RemoteViews;
import android.widget.RemoteViewsService;

/**
 * Created by the-dagger on 24/7/16.
 */

public class WidgetDataProvider implements RemoteViewsService.RemoteViewsFactory {

    private Context context;
    private Cursor cursor;
    private Intent intent;

    //For obtaining the activity's context and intent
    public WidgetDataProvider(Context context, Intent intent) {
        this.context = context;
        this.intent = intent;
    }

    private void initCursor(){
        if (cursor != null) {
            cursor.close();
        }
        final long identityToken = Binder.clearCallingIdentity();    
        /**This is done because the widget runs as a separate thread 
        when compared to the current app and hence the app's data won't be accessible to it
        because I'm using a content provided **/
        cursor = context.getContentResolver().query(QuoteProvider.Quotes.CONTENT_URI,
                new String[]{QuoteColumns._ID, QuoteColumns.SYMBOL, QuoteColumns.BIDPRICE,
                        QuoteColumns.PERCENT_CHANGE, QuoteColumns.CHANGE, QuoteColumns.ISUP},
                QuoteColumns.ISCURRENT + " = ?",
                new String[]{"1"},null);
        Binder.restoreCallingIdentity(identityToken);
    }

    @Override
    public void onCreate() {
        initCursor();
        if (cursor != null) {
            cursor.moveToFirst();
        }
    }

    @Override
    public void onDataSetChanged() {
        /** Listen for data changes and initialize the cursor again **/
        initCursor();
    }

    @Override
    public void onDestroy() {
    cursor.close();
    }

    @Override
    public int getCount() {
        return cursor.getCount();
    }

    @Override
    public RemoteViews getViewAt(int i) {
        /** Populate your widget's single list item **/
        RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.list_item_quote);
        cursor.moveToPosition(i);
        remoteViews.setTextViewText(R.id.stock_symbol,cursor.getString(cursor.getColumnIndex(QuoteColumns.SYMBOL)));
        remoteViews.setTextViewText(R.id.bid_price,cursor.getString(cursor.getColumnIndex(QuoteColumns.BIDPRICE)));
        remoteViews.setTextViewText(R.id.change,cursor.getString(cursor.getColumnIndex(QuoteColumns.CHANGE)));
        if (cursor.getString(cursor.getColumnIndex(QuoteColumns.ISUP)).equals("1")) {
            remoteViews.setInt(R.id.change, "setBackgroundResource", R.drawable.percent_change_pill_green);
        } else {
            remoteViews.setInt(R.id.change, "setBackgroundResource", R.drawable.percent_change_pill_red);
        }
        return remoteViews;
    }

    @Override
    public RemoteViews getLoadingView() {
        return null;
    }

    @Override
    public int getViewTypeCount() {
        return 1;
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }
}

Let’s also create a service that invokes the WidgetDataProvider after a fixed interval

import android.content.Intent;
import android.widget.RemoteViewsService;

/**
 * Created by the-dagger on 24/7/16.
 */

public class StockWidgetService extends RemoteViewsService {
    @Override
    public RemoteViewsFactory onGetViewFactory(Intent intent) {
        return new WidgetDataProvider(this,intent);
    }
}

Phew.. almost done with this now.

Finally edit up the widget_info.xml located inside /res/values/xml/ of your project.

Edit it to reference the time after which your widget will be updated, the preview image which should show up in the widget picker and minimum width and height of the widget.

<?xml version="1.0" encoding="utf-8"?>
<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:initialKeyguardLayout="@layout/app_widget"
    android:initialLayout="@layout/app_widget"
    android:minHeight="110dp"
    android:minWidth="170dp"
    android:previewImage="@drawable/example_appwidget_preview"
    android:resizeMode="horizontal|vertical"
    android:updatePeriodMillis="86400000"
    android:widgetCategory="home_screen"></appwidget-provider>

Well, once this is done, go ahead and fire up your app. You will be able to see the newly created and updated widget in your homescreen.

 widget

Pretty awesome right!
Congratulations on making your first widget.

For now the app only opens a specific activity on clicking it, but you can read up a bit on how to execute a separate task on clicking each item on the list by using a pendingIntent.