Category Archives: Retrofit

Rebuilding a legacy app from scratch: MadridBus revamp (I)

MadridBus was the second application that we released in Quoders to the app store. It is an adaptation from the original BilbaoBus, an app to get public transport information like routes, stops info, timetable, etc. It was born just as a learning side project but we got good traction from the beginning  and it grew up having more public transport agencies, improved UI, etc.

screen-shot-2016-10-01-at-09-27-38On the other hand MadridBus wasn’t so popular, probably because there were already a few decent applications in the market for the city of Madrid, so we didn’t focus so much on it. As a result, now days the app looks and feel really outdated, the UI is clunky and the plumbing of the app are really ugly and not maintainable.

So for this reason I have decided to rebuild the app from the scratch as one of my side projects. It will be open source published in Github. I will be explaining here in the blog all the design and implementation decisions, the different techniques, libraries, etc. The goal, apart from having a new and better application, is to have a project that could be a reference for new Android developers and hopefully help them to have a better understanding in how to implement from zero an Android app following good practices, patterns and explain the usage of Android concepts and most used libraries.

In this post I am going to give a quick summary of the different features, patterns, design and other elements that I am going to use following the best practices and modern Android development techniques. In following post I will be describing in more detail each of these elements and explaining the implementation and the source code will be available on Github.

Minimum Viable Product scope and features

So first thing first, let’s define the MVP (Minimum Viable Product) features and requisites.

The current published version of MadridBus has five main features:

    • Go To: This feature allows the user to search a route between point A to B, either pointing in the map or searching by address. This functionality, despite being really useful when you don’t know the city or the best route, interestingly it’s not very used as our Google Analytics data reveals.
    • Line List: Display the list of all the lines (day and night) available and allows the user to see the stops for a specific line and then the next bus time.
    • Stops List: Display a list of all the bus stops in the network. This functionality again is not really very useful, unless you know the name of the stop and want to look up.
    • Favourites: This is really useful as the user can save here to have quick access to the favourites stops, like work, home, etc.
    • News: Display a list of news fro the rss service of the bus agency. Useful when there are disruptions, changes, etc.

So for the MVP of the new app, taking into account what features the users are really using in the published app,  I’m going to go for the Line List, Favourites and News. Also we will be releasing an Android Wear app that will displayFor the V2, we will be adding the Go To feature and maybe the Stops list.

App architecture: Data access and storage

A public transport application needs to work with an extensive and complex source of data containing lines information, time tables, real time, geolocation, etc.

For MadridBus we are going to need two different set of data that we will retrieve from the Madrid public transport agency web servers:

The first one are static data that needs to be downloaded periodically and stored in the device for quick access offline.  This set of data contains the bus lines info, route s, stops position, etc.

The second type of data are the real time information, this will be accessed when we needs to display the real time info of the next bus for a specific stop.

To accomplish this network access we are going to use the well known library Retrofit from Square.  There are other options like Volley from Google but in my personal opinion and as you can see in some reviews like this, Retrofit is much better option. For more information you can check my blog post about Retrofit.

For the data storage on the device we are going to use a local data base managed with the library Realm. Databases in Android usually is a pain to implement using the SQLite API, but with real we simplify and make more robust and less error prone our data base implementation. It supports multithreading, encryption, reactive extensions, etc.

UI Layer: Material design

So now let’s talk about the UI layer. As we mentioned before, for the version 1 we are going to implement just the Line list, Favourites and News functionalities.

We can see clearly three different features that will need three direct access from the home screen. So following the Material Design guidelines we are going to use the recently added Bottom Navigation widget that will give us access to the three different features of the app. As we can see in the documentation,  this component is recommended for between three and five sections. In case we needed more is recommended to use a Tab view component or maybe using the left navigation drawer.

So the first option is the Home view and it will display a Google Maps showing the location of the user and the nearest bus stops. The second option will be the Line List, using a Recycler view to display the lines info, and the third option will be News screen, again using a Recycler view. We will post designs and wireframes in a future post when we start implementing this.

UI Layer: The MVP pattern

The MVP is now days one of the most used patterns in the Android community  when it comes to organise the UI layer. There are multiple benefits like much more modular, reusable and testable code. For a complete description and explanation of the pattern take a look to one of my previous blog post.

As a quick summary, the Activities, Fragments and custom views will be the View layer of the pattern and they will contain only pure UI functionalities.

The Presenter will be a man in the middle layer that will work as intermediary between the Views and the Model. They will respond to events and actions from the user on the View and it will perform any action required using the Model layer.

Modules wiring and communication

So as we are going to have different layers in the app following we need some mechanism to communicate with each other, passing data, etc.

There are different ways to accomplish this, we have just the traditional way using listeners, but we agree that this comes with many problems and we end up with the infamous hell of listeners.

Another better solution would be using an event bus, but this again has its own downside. The code end up being less readable it grows up having multiple events dispatching from everywhere with unexpected results.

There is a better solution and will be using RxJava. As we know it’s one of the library and techniques that has focused the attention of the Android community for a while now.

We will see in a future post and in the code of the app how to use RxJava and how to architect the app using it and all the benefits that it has. In the mean time you can have a look to my blog post about it.

Testing and Continuous Integration

Testing is often one of the most neglected aspects of the applications development process. For our application we are going to implement two main type of test: Integration Test using Espresso (UI test) and Unit Test when relevant with JUnit.

For more information about a good testing strategy take a look to my blog post about it.

Continuous Integration is another key piece of our app development as it allows us to have a build of our app everytime we submit changes to the code repository. This way we can launch our tests suite every time we make a change in the code validating it’s correctness.

For this functionality we are going to use Travis, a CI platform totally free for open source projects. Once again we will be explaining the configuration in next posts.

Summary

So that’s it for today, as mentioned before we are going to be publishing blog posts to comment and explain the implementation of the different parts of the new app as we progress coding it.

Stay tuned!

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Introduction to Android HTTP communication with Retrofit

In a previous post I described how to implement HTTP requests using the Google’s library Volley. We saw how to save lot of boilerplate code in such a critical part of our apps like the networking communication with our server using a well tested and reliable library.

We showed how straightforward is to have so useful features like parallel HTTP requests, cancel petitions, image downloads caching, etc.

But Volley is not our only option, there are more libraries out there that does a really good job,  and one of the well known and widely used is Retrofit from the Square people.  In this post you can find a very good comparison  between the two libraries where Retrofit would win as it is faster that Volley, but you better try and test by yourself and check which one would fit better on your project.

You can find here in my AndroidBootstrap project in Github how to integrate the library in an Android Studio project and a few examples of use.

 

Integration in our project

You can download the library .jar from here or if you’re using Maven:

<dependency>
 <groupId>com.squareup.okhttp</groupId>
 <artifactId>okhttp</artifactId>
 <version>2.0.0</version>
</dependency>
<dependency>
 <groupId>com.squareup.okhttp</groupId>
 <artifactId>okhttp-urlconnection</artifactId>
 <version>2.0.0</version>
</dependency>

Or if using Gradle:

compile 'com.squareup.retrofit:retrofit:1.9.0'

 

Retrofit client

The first thing we need to do is to initialise the Retrofit rest client object. You might want to use a singleton to manage the life cycle of the client if you’re planning to do frequent request on your app:

public class RestClient {

    private static final String API_URL = "http://jsonplaceholder.typicode.com";

    private static RestApi mRestApi = null;

    public static synchronized RestApi getInstance() {

        if(mRestApi == null) {

            RestAdapter adapter = new RestAdapter.Builder()
                    .setEndpoint(API_URL)
                    .build();

            mRestApi = adapter.create(RestApi.class);
        }

        return mRestApi;
    }
}

 

A simple HTTP GET request

Retrofit uses Java interfaces and annotations to define the REST API requests. Then it will generate the necessary code thto perform the HTTP requests and finally will convert the Json response in the specific pojo object using Gson.

Let’s take a look to this example:

@GET("/comments")
void getCommentsAsync(@Query("postId") String postNumber, Callback<list> callback);

As you can see “@GET” specifies the type of request and “/comments” is the path of the request.

Then we have the “@Query” annotation that specifies the addition of a param to the url which will take the value of the param “postNumber”.

Finally we can see the Callback parameter where retrofit will retrieve the object that has been created from the Json response using the Gson library.

In case we need to do a synchronous request the interface will look like this:

@GET("/comments")
List getCommentsSync(@Query("postId") String postNumber);

If we need to perform a POST operation:

@POST("/comments")
void postComment(@Body CommentItem item, Callback cb);

And if we need to add headers to our request:

@Headers("Cache-Control: max-age=640000")
@GET("/comments")
List getCommentsWithCustomHeader();

 

So this is a very brief introduction to the Retrofit library. As mentioned before you can find examples of the use and integration in my Bootstrap Android project. I’ll be adding more examples of useful libraries or snippets in the future.

And finally if you have any comment or suggestion please don’t hesitate in leave it below!

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