5. Multiplatform Mobile dev.

This small Section is completely optional, and not part of the core contents of this course. It showcases other possibilities for mobile app development, broken free from the solitary confinements of Android native code.

1. Other Native Solutions

Not everyone buys Android-based phones. Apple’s iPhone is arguably (much) more popular, and is based on iOS. Developing apps for iOS is a totally different development experience: it requires other tools, another language, and other deployment chains. This is a bad thing: it means you will have to learn to live in both worlds if you intend to release your software on both operating systems!

Development of iOS apps is done through the Xcode IDE, a proprietary IDE that only runs on MacOS. That’s right, you’ll need a Mac machine to build and deploy native iOS apps.

To program iOS apps in Xcode, you write code in Swift, a programming language created by Apple in 2014 built on top of the LLVM environment. Swift serves as a replacement for Apple’s older Objective-C that originated in the eighties. One of its strengths is its flawless interoperability with Objective-C, like Kotlin has with Java. Swift is also statically typed and also uses smart inferred typing. They both are relatively modern languages. A few similarities and differences:

val immutable = 55
var somevar: Double = 33.0

fun greet(name: String, day: String): String {
    return "Hello $name, today is $day."
}

let immutable = 55
var somevar: Double = 33

func greet(_ name: String,_ day: String) -> String {
    return "Hello \(name), today is \(day)."
}

And then there’s SwiftUI:

SwiftUI is a framework to build User Interfaces (UI) for iOS apps. With SwiftUI, you create the UIs of your iOS apps entirely with Swift code, using a novel declarative approach.

We would have loved to introduce you to the world of iOS development for a single class, but that would mean everyone must have access to Apple hardware.

Still, if you’re serious about app development, the question isn’t “which language will I learn” but “which will I learn first”. You simply cannot ignore the iPhone market!

2. Multiplatform Mobile

2.1 The Kotlin Way: KMM

To ease the development pains that come from maintaining two different code bases in two different languages, using two different IDEs, Kotlin introduced the KMM, or the Kotlin Multiplatform Mobile system. Get familiar with KMM here.

In essence, KMM enables you to write and maintain a shared code base for your domain logic, while it splits the UI logic to both OSes' unique capabilities, written either in Android’s Activity/Fragment/Intent system, or using SwiftUI. Your code base will look like this:

src
    | androidMain
        | MyActivity.kt
    | androidTest
    | commonMain
        | MyObject.kt
    | commonTest
    | iosMain
        | MySwiftUIWindow.swift
    | iosTest

The KMM platform: shared Kotlin business logic takes the center.

KMM will scaffold certain Swift files for you: it will generate parts of the Swift code, making it easier for the developer to build a single interface for both OSes. See the make your android application work on iOS tutorial for more in-depth information. KMM’s case studies, and especially the Netflix migration blog post are interesting reads.

You will still need access to both the Xcode and Android Studio toolchain. Therefore, we will again leave it up to the curious student with access to a Mac to discover KMM’s capabilities.

2.2 The Microsoft way: Xamarin

Microsoft developed the freely available Xamarin framework, which is:

Free. Cross-platform. Open source.
An app platform for building Android and iOS apps with .NET and C#

Using Xamarin, you can develop your apps in C# but still deploy on iOS and Android. It is fully cross-platform, and still builds natively. As the site states, Anything you can do in Objective-C or Java, you can do in C#. Looking a bit further, you will still notice two separate docs pages for iOS and Android, as the namespaces and framework libs differ quite a bit. The language might be the same, but the underlying principles are not. This is in line with what KMM tries to do.

3. Mobile Web Tools

Both leaning on Kotlin/Swift and KMM requires heavy investments. What if you could develop mobile apps in a language you’re already familiar with? Many companies opt for a JavaScript-powered solution instead, as they employ web developers that not necessarily need to take the time to learn a new web-based framework. This is a rapidly changing environment, meaning many frameworks came and went:

Web development techniques will be explained in detail in the cloud computing course in the master year.