Building a Cordova App

In an earlier post I wrote about the golf score tracking application I created to learn ASP.NET Core and AngularJS. Since the initial inspiration was my son playing golf, I thought it would be good to put the application on his tablet so he could track his own scores. Cordova looked like the technology to allow me to turn my "experiment" into something my son could practically use.

I'm going to focus on my experience with Cordova and getting a mobile app running. (I'm writing this post mostly so that I don't forget the little things I ran into while getting things to work.)

Cordova is an Apache open-source project for building mobile applications using web-based technologies. I have heard about this technology for a few years at several tech conferences that I attend. The appeal of Cordova is that it should allow a developer to publish an application to multiple mobile platforms using the web-based technology that is already known. Cordova was born out of a technology called PhoneGap.

The Cordova utilities run on Node.js and can be installed using the Node Package Manager (NPM). The Getting Started page of the Cordova site has all of the basic steps necessary to get Cordova installed and the first application created. Here are the steps I followed:

1. Install Cordova.

   npm install -g cordova

2. Create a Cordova application.

   cordova create com.darrenhale.golfscoretracker golfscoretracker

   This step is different than the step listed on the Cordova Getting Started page. I was required to include the "com.darrenhale.golfscoretracker" portion to generate the application structure.
3. A Cordova application has to have "platforms" added for the deployment targets. I wanted my application to function in the browser, on Android, and on iOS

   cordova add platform browser android ios

4. Migrate the "web" application into the Cordova application structure. For me this meant:
   1. Copying my index.html page into the www folder of the Cordova application.
   2. Copying my Javascript files into www/js folder.
   3. Copying my bower_components folder into the www folder.
   4. Copying my css folder into the www folder.
   5. Copying my styles folder into the www folder.
   6. Making any path changes to the files referenced in index.html
5. At this point, I tried running the application in the browser.

   cordova run browser

Up to this point, things were great! The application worked when I called:

cordova run browser

I had also started my web API application to have a back-end process. Everything worked as expected! (I expected it to work since the AngularJS app worked in a browser already.) My next step was to run it for a mobile platform.

In my excitement, I quickly executed:

cordova run android

Guess what happened? Nothing. It was late, and I realized I was not thinking straight. It dawned on me that I needed an Android emulator to make this command work. Let the adventure begin!

At my next opportunity to work on the project, I immediately went to get the Android SDK and its corresponding emulator. I didn't realize how much the state of mobile development has changed, and I was surprised to find that the first thing I found was Android Studio. I really didn't want to download a full development environment. After some poking around I was able to find just the Android command line tools. I downloaded the package for Mac OS X and unzipped the package into a folder on my system.

I created a test device to emulate for running my application. Through trial and error, I came up with the following configuration:

• Targeted Android 6.0 - API Level 23
• CPU/ABI of ARM (armeabi-v7a)
• RAM of 512
• VM Heap of 32
• Internal Storage of 200 MiB
• Emulation Options: I selected Use Host GPU

I could now successfully start the Android emulator and interact with it. (It is important to note, the emulator is VERY SLOW to start completely. Give it time to start up.)

With the emulator running, I executed:

cordova run android

The Cordova utilities packaged my application, pushed it to the emulator, and started the application. It worked! My application started up and functioned! I realized I needed to adjust the CSS in the app to work on a smaller display, but those changes were straightforward to make. After a little more trial and error, I had an application that functioned on a mobile device.

The last change I needed to make was to replace the API calls in the application with calls to localstorage. I opted to use localstorage for two reasons: first, I wanted my son to be able to use this application without any network connectivity, and second, localstorage is a mechanism that a Cordova app can use across multiple platforms. Localstorage is essentially a key/value store using JSON as the storage mechanism. Most of the data in the golf score app is pretty simple, so I figured I could make this work. The localstorage object has a setItem() method for saving data and a getItem() method for retrieving data. I was able to replace my API calls with localstorage calls fairly easily, but the app didn't work right away. The trick I was missing was that I needed to convert my objects into a JSON format to save them and to parse JSON into my object when retrieving them. I accomplished this with JSON.stringify() and JSON.parse() respectively.

My path for learning Cordova is not unique, and I'm sure many of the challenges I have experienced aren't challenges for experienced mobile developers or Javascript developers. It was still a great learning experience and it has me excited to do more Javascript coding!