4. Android Development in Kotlin – Some Advance Concepts¶

¹ ² App Bundles¶

App Bundle:
- It is the compiled version of any kotlin/java code, along with any resources and static files that are needed for the app to run.
- It used to be a bundle for each device architecture, but now it is a single bundle for all architectures that should be submitted to the play store.
- The play store takes the bundle and generates the a signed APK bundle for each device architecture.
The App bundle is not a full APK, thus it can NOT be installed on a device, however it can be used to generate a signed APK, which Google Play does on your behalf.
The Play Store generates hundreds of signed APKs from the app bundle, each signed APK is optimized for a different device configuration.
bundletool is a command line tool that can be used to:
- Generate APK set from an app bundle, targeting a specific device configuration(s).
- Deploy an app bundle to a connected device.
- Perform E2E testing on a device using an app bundle and test APKs.
- Estimate the download size of an app bundle.
Basically, Google Play uses the same bundletool, so it is a good way to experiment with changes before submitting to the Play Store.

³ SQLite Database in Android¶

You can use SQLite to create databases on the user’s device and access them from your app at any time.
It is an Offline database on the user’s device, thus, no internet connection is required to access it.
The data is stored in a text file that’s convenient for SQLite engine to read and write.
The permissions required to use SQLite are:
- android.permission.READ_EXTERNAL_STORAGE
- android.permission.WRITE_EXTERNAL_STORAGE
- add them to the AndroidManifest.xml file in a <uses-permission> tag.

⁴ ⁵ Network Connection in Android¶

The Android platform includes the `HttpsURLConnection`` client, which supports TLS, streaming uploads and downloads, configurable timeouts, IPv6, and connection pooling.
Third party libraries: Retrofit (on top of OkHttp), and Ktor (kotlin native, uses coroutines, be JetBrains).
The DnsResolver interface can be used to resolve host names to IP addresses, and vice versa.
Use the Repository pattern to abstract the data layer from the rest of the app.
Network requests can NOT be done one the main thread, as a NetworkOnMainThreadException will be thrown.
Functions that perform network operations should be called from a coroutine or from a different thread (aka, should be suspend functions).
The ViewModel class is designed to store and manage UI-related data in a lifecycle conscious way. That is, it holds component state between renderers (analogy to useState in React).
Best practices:
- Before doing a request, check the network connection using ConnectivityManager or NetworkInfo.
- Avoid large data transfers if device is not connected to a Wi-Fi network.

⁶ ⁸ Exceptions in Kotlin¶

Kotlin Try Catch is used to handle the code that could throw an exception at run-time.

try {
   //code that code potentially throw and exception
 } catch(e: Some_Exception) {
   //code to handle if this exception is occurred
 } catch(e: Exception) {
   //you can have multiple catch blocks
   //code to handle if this exception is occurred
 } finally {
   //code that will be executed regardless of whether an exception is thrown or not
 }

 val x = try { someFunction() } catch(e: Exception) { 0} //x will be 0 if an exception is thrown from someFunction()

Exception is the parent class of all exceptions in Kotlin.
Other exceptions include: ArithmeticException, IOException, ClassNotFoundException.
Exceptions that do not have a suitable catch block are called uncaught exceptions, and they will cause the app to crash (still be throw even if you have a catch block for other exceptions).
Exception has:
- message property: a string that describes the exception.
- printStackTrace() method: prints the stack trace of the exception.
Ypu can throw Exception("message") to throw an exception.
Error and Exception are both subclasses of Throwable, but Error is used to indicate serious problems that a reasonable application should not try to catch, while Exceptions are caught.
Example of errors: OutOfMemoryError, StackOverflowError.
To catch all exceptions (including errors), use catch(e: Throwable).
checked exceptions are java feature where a function states what errors it throws, and the callers must handle them. Kotlin does not have this feature.

⁷ ⁹ Generics in Kotlin¶

class TouchedByAnAngle<T> {
    private T thingy;
    public T getThingy() { return thingy; }
    public void setThingy(T replacement) { thingy = replacement; }
}

val m = TouchedByAnAngle<Int>()
m.setThingy(5)
m.getThingy() //5

data class Person(val name: String, val age: Int)
val p = TouchedByAnAngle<Person>()
p.setThingy(Person("John", 20))
p.getThingy() //Person(name=John, age=20)

Any is possible to be used as a generic type, but it is not recommended.

val critters = mutableListOf(Frog(), Axolotl(), "ribbit!") //MutableList<Any> as Any is the parent of all classes in the list

Advantage of generics: Type safety, no need for type casting, and compile time checking.
As extension function allows to add methods to class without inherit a class or any design pattern.

¹⁰ Emulator¶

Advantages of Emulator: Flexibility (run any Android version, any device, any screen size), Simulate any thing (GPS, network, battery, etc), and Test apps without physical device faster.
Android Virtual Device (AVD): is a configuration that defines the characteristics of an Android phone, tablet, Wear OS, Android TV, or Automotive OS device that you want to simulate in the Android Emulator.
The Emulator saves the state of each AVD between each session; the data is stored under a specific folder in the user’s home directory.

References¶

About android app bundles. (2022, March 17). Android Developers. https://developer.android.com/guide/app-bundle ↩
Build and test your android app bundle. (2021, July 17). Android Developers. https://developer.android.com/guide/app-bundle/test ↩
Chaitanyamunje. (2021, February 25). How to create and add data to SQLite database in Android? GeeksforGeeks. Retrieved July 3, 2022, from https://www.geeksforgeeks.org/how-to-create-and-add-data-to-sqlite-database-in-android/ ↩
Connect to the network. (2022, June 21). Android Developers. https://developer.android.com/training/basics/network-ops/connecting ↩
Kamal, F. (2020, April 6). Android networking with kotlin tutorial: Getting started. raywenderlich.com. https://www.raywenderlich.com/6994782-android-networking-with-kotlin-tutorial-getting-started ↩
Kotlin exceptions. (2021, January 21). TutorialKart. https://www.tutorialkart.com/kotlin/kotlin-exceptions/ ↩
Kotlin generics. (n.d.). javaTpoint. https://www.javatpoint.com/kotlin-generics ↩
Murphy, M. L. (2021). Elements of kotlin. CommonsWare. https://commonsware.com/Kotlin/Kotlin-FINAL.pdf licensed under Creative commons 4.0. Chapter 18: Exceptions. ↩
Murphy, M. L. (2021). Elements of kotlin. CommonsWare. https://commonsware.com/Kotlin/Kotlin-FINAL.pdf licensed under Creative commons 4.0. Chapter 17: Generics. ↩
Run apps on the android emulator | Android developers. (2021, October 28). Android Developers. https://developer.android.com/studio/run/emulator ↩

4. Android Development in Kotlin – Some Advance Concepts¶

1 2 App Bundles¶

3 SQLite Database in Android¶

4 5 Network Connection in Android¶

6 8 Exceptions in Kotlin¶

7 9 Generics in Kotlin¶

10 Emulator¶

References¶

¹ ² App Bundles¶

³ SQLite Database in Android¶

⁴ ⁵ Network Connection in Android¶

⁶ ⁸ Exceptions in Kotlin¶

⁷ ⁹ Generics in Kotlin¶

¹⁰ Emulator¶