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Consuming a JSON REST API in Android

JSON REST API

This week’s blog post was requested by one of our readers, Jasmine.

Jasmine asked if I could write a guide on “processing JSON data for android applications using NodeJS and Express and Android Studio”.

I haven’t done anything using Android Studio in a while – and I love writing guides that you all want and need – so I thought I would give it a shot.

There are two parts to processing JSON data in Android using NodeJS and Express:

  1. Writing an app capable of processing the JSON data.
  2. Writing a backend capable of producing the JSON data to be processed.

Because there are two parts to this, naturally I’ve broken the steps down into two blog posts.

In the first guide – i.e. this one – l’ll walk you through step #1 and teach you how to create an Android app using Android Studio, which allows you to process JSON data from a REST API.

The next post will show you how to make a REST API using NodeJS and Express. (Check back next week, or better yet, sign up to my newsletter).

Alright, so let’s get started.

In this guide I’ll teach you how to make an Android app which uses the latest Volley HTTP library and allows you to efficiently make network requests and handle the response.

The app will have a text field where you can enter a GitHub username and a button that will retrieve a list of all public GitHub repositories for the provided username.

The repos will be listed in a text box with the name and last updated date.

Create Our App

Open up Android Studio and create a new project.

Next, fill out the new project form by entering the following:

Application Name: AndroidJsonParser

Company Domain: (Your company domain, or if you don’t have one, use example.com).

Then, click Next.

In the Target Android Devices screen, leave everything as default and click Next.

On the Add an Activity to Mobile screen, choose Empty Activity and then click Next.

On the Customize the Activity screen, leave everything as default and click Finish.

Wait a minute or two for the project to load…

Enable Volley and Internet Access

Let’s add the Volley library to our project.

In the Project Explorer, navigate to Gradle Scripts > build.gradle and add the following to the dependencies:

Save the file.

Then, in the Project Explorer navigate to and open app > manifests AndroidManifest.xml.

Just above the application tag, add the following line to add the INTERNET permission:

Modify the Layout

Next we are going to want to add the following elements to our activity layout:

  • EditText for a GitHub username
  • Button for getting the data once the username is entered
  • TextView for showing our results

That’s the minimum required for an effective demo.

In the project explorer, navigate to appreslayoutactivity_main.xml. Once the file opens, select the Text tab at the bottom of the screen.

Now, let’s remove the existing Hello World! text view, and add the following code:

Write our Java Code

Now, let’s write the logic for our app.

The first thing we’ll do is import the packages we need to make our app work.

You can actually do this as you go along, using the Alt Enter shortcut to auto-import. However, I found this didn’t work for all of the imports (some of the Volley and JSON packages I needed to import manually).

For simplicity, lets delete any existing import statements, and replace with the following (note: make sure you leave the package declaration on the first line, as this will be different for each person).

It will look something like this

The reason some are grey is because Android Studio is letting us know which ones are unused. Don’t worry, we’ll use them later.

Now let’s add some instance variables. Instance variables are defined when we initialise our app. These variables are used in various methods later on in the code.

We define them immediately below the “Public class MainActivity…” and above the first “@Override” statement:

So our code now looks like this:

Getting there…

Next, let’s update our “onCreate” to register our views and setup our queue. As the name suggests, “onCreate()” is the function that is created when our Android Activity (the screen in-front of our code) is created.

We need to link the view elements we created earlier (the text input, button and text output) with the instance variables we defined above, so we can use them in our code.

Update the onCreate method to look like this:

So now our code looks like this:

Next, let’s add some helper functions to our code.

I described what each function does in the comments block.

Insert the following below the onCreate() block which we just updated (below the end bracket):

So the code will look something like this:

Alright, so this is the part where we make our HTTP request.

Insert this code underneath our last function (setRepoListText). This code might look confusing but it’s actually quite simple. I’ve described what each section does in the inline comments. If you want to gain a more in-depth understanding, I highly recommend you read the official guide Transmitting Network Data Using Volley.

Now our code looks like this:

One final code change to make. You may have noticed above that in our Layout Snippet we added the following on line 25:

This basically tells Android that when the user clicks that button, call the getReposClicked() function in our app.

So the last step is to define this function.

Add this code below the Volley function we just added:

Now the code looks like this:

Alright, the code is complete!

Test Our App

Finally, let’s test our app.

At the top of Android Studio, click on the play button:

In the Select Deployment Target screen, choose either a Connected Device (if you have a real Android Device that you use to test your apps on), or a device under Available Virtual Devices.

If you don’t already have a device setup, then you can click on Create New Virtual Device and follow the steps on-screen to create a new one.

Alright, once that’s done, your app should load on the selected target.

Test it out! Enter your GitHub username and watch it retrieve a list of all your GitHub repos right before your eyes.

I hope this helped Jasmine?

If you have any questions, feedback, or want me to cover a specific topic, please let me know in the comments below!

Cheers
Mark

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