How to call Functions from Android

Twilio Functions are a perfect fit for mobile app developers. You can focus on writing your app, and let Twilio host and run the server code you need.

You don't need a special Twilio SDK or library to call Twilio Functions from your mobile app—your Function will respond to a normal HTTP call. We'll use Google's Volley HTTP Networking library with this example, but you can use other HTTP libraries for Java or Android if you would like.

In this guide, we'll show you how to set up a Twilio Function, call it from a web browser, and then call that function from an Android application. Our function will return a joke as a string. You could extend it to make it choose a random joke from a list, or by category. We'll keep it brief, and just return a hard coded string.

Let's start by creating a Function and giving it the path of /joke. Be sure to set the visibility of this Function to public, to avoid any hurdles when making your HTTP calls:

With the Function created, we'll need to edit the boilerplate code that is generated for the Function—by default, it comes with some code to return TwiML. We're only going to return a joke. And it's a bad joke.

Copy the above code into the Twilio Functions code editor. Please, change the joke to something better. Press the Save button to save that code, and click Deploy All to deploy your Function.

Call a Twilio Function from the Web

To call your new Function from the web, get the Function's URL by clicking the Copy URL icon next to the path, and then paste that URL into any web browser (you don't have to be authenticated with Twilio). You'll get a text response containing whatever you return from your Function!

Call a Twilio Function from Android

We are going to use Google's open source Volley library to call our Twilio Function. Volley is a great choice, and provides built-in request classes for retrieving strings, JSON objects, and JSON Arrays.

Volley is not part of the Android SDK. You will need to include the Volley library in your build.gradle file as a dependency, like this:

dependencies {
    ...
    compile 'com.android.volley:volley:1.0.0'
    ...
}

If you are using Android Studio, be sure to Sync your gradle file after this edit.

Don't forget to also put the INTERNET permission request into your AndroidManifest.xml file as well, or you will get an exception when you make an HTTP request.

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

The Volley StringRequest constructor takes the HTTP method used (GET in our case), the URL to retrieve, and two listeners—one for a successful response, and one if there is an error. The onResponse and onErrorResponse methods will be on the main (UI) thread, so you can modify the user interface. In our case, we are just going to log the responses to the console.

Return JSON from a Twilio Function

Our previous example Function returned plain text. You can also return JSON from a Twilio Function, by passing a JavaScript object or array to the callback function. For instance, we can create another Twilio Function to return a list of jokes, along with an id and a favorite count. Create a new Function with a path of /jokes.

Parse JSON from a Twilio Function

From Android, we call this Function the same way that we did our first Function (don't forget to change the path to /jokes). We can use Volley's JsonArrayRequest object similarly to how we used StringRequest before.

You've now seen how to run Node.js code as a Twilio Function, and how your mobile application can use this as a serverless backend to provide data for your application.

Where to go next? You could extend the Function to choose a random joke from that array. You can also use Twilio functionality from inside your Function, for instance to send an SMS, or to return an access token for Video, Chat, or Sync. Check out the Programmable SMS Quickstart for Twilio Functions and Programmable Voice Quickstart for Twilio Functions for more quick introductions to these key features of Functions.