Download Files in Android - Kotlin & Java

Unless you are writing a Download Manager, downloading files in an Android application is never going to be the main business logic to solve but based on the requirement, you may need to download metafiles, media files, or documents over the Internet within your Android application. However, a reliable solution to download files in an Android application poses its own challenges including but not limited to the following list:

1. Thread Management

IO operations must be executed in a separate thread. Though there are plenty of options to achieve this such as now deprecated AsyncTask, Kotlin coroutines, or RxJava, still complex for a novice developer to properly handle the concurrency problems. Sending signals to the downloading thread to cancel or pause the download may introduce additional synchronization issues.

2. Error Handling

What if the Internet connection dropped while downloading the file? What if the application is closed while downloading/saving the file? How to handle all HTTP errors? the list goes on. Addressing all these scenarios is tedious and most of the time not possible.

3. Updating the UI

While downloading the file in a separate thread, updating a progress bar in the main thread is a challenge unless the concurrency framework you use provides an easy way. The same goes to update the UI after the file is downloaded.

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Android: List External Storage Files

This article explains how to list files from the external storage (SD Card) in Android. Though you can list files recursively using a simple method, the new Runtime Permission Model introduced in Android 6 makes it a little difficult. Let's dive into the code and see how we can list all the files recursively.

As I mentioned earlier, I am using Kotlin for Android development since it is the future of Android. If you are using Java, just copy and paste the code into your class method by method. The Android Studio will translate the method into Java for you.

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Android: Custom Font in Kotlin

Sometimes you may want to use custom font in your Android application for aesthetic requirement or to show a message in a different language. I have already written an article on how to use a Custom Font in Android four years ago. Since it has been a long time and a reader wondered if that code still works, I am writing this new article using Kotlin. However, the underlying technique hasn't change over the years and you can still use my previous article.

Step 1:

Create an Android application "Custom Font" with Kotlin support.

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Access MySQL from Android through RESTful Web Service

Finally, I found some time to write about accessing MySQL or any database that you can think about from an Android application. Android offers a built-in database known as SQLite which is supposed to be used for local data storage. For example, if you want to store your recent transactions locally in the device, you have to go with SQLite. I have already written a few articles on how to use SQLite database in Android. However, enterprise mobile applications often depend on client/server databases such as MySQL, Oracle DB or MongoDB. Whatever the database, you have chosen, the way to access them from an Android application is pretty same. In this article, I explain how to access a MySQL database from an Android application written in Kotlin.

I will use Kotlin for all upcoming Android tutorials because it is the future of Android programming. Kotlin is a JVM based language and you can easily convert a Kotlin project into Java and vice versa.

An Android application is not supposed to directly access a database deployed in a server. I do not recommend implementing JDBC connections in an Android application due to the tight coupling introduced between the application and the database. The industrial best practice requires you to implement a web service between the database and the Android application. Having a web service layer reduces the complexity of the Android application and also reduces the dependency on database specific operations. Therefore, the problem of accessing a client/server database like MySQL from an Android application can be defined as the problem of consuming a web service hosted somewhere.

Having said that, as an Android developer, you don't need to care about what is behind the web service. It may be a MySQL database, MongoDB database, a Social Media network or even a Weather Network API. What you need is the API endpoints exposed by the web service. In this article, I only explain how to connect to a web service hosted on your local machine from an Android application. However, the sample web service used in this article provides API endpoints to CRUD operations on a MySQL database. Please follow the RESTful CRUD With Java and MySQL in Minutes article and develop the web service to access a MySQL database. In the following section, you will learn how to access the web service you have created for accessing a database.

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Android: Simple Calculator in Kotlin

It has been a long time since I wrote the tutorial: Android: Simple Calculator. However, still, that tutorial attracts more readers to my blog. Therefore, I have decided to write a new article to develop the same application using Kotlin. The previous article on developing a Calculator application using Java is still valid and feel free to compare this article with the previous one.

Step 1:

Create a new Android application: Kotlin Calculator with an Empty activity. In the very first dialog, make sure that you have enabled the Kotlin support.

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