Category Archives: Kotlin

Dependency injection

In software engineering, dependency injection is a technique in which an object receives other objects that it depends on. These other objects are called dependencies. In the typical “using” relationship the receiving object is called a client and the passed (that is, “injected“) object is called a service.

The code that passes the service to the client can be many kinds of things and is called the injector. Instead of the client specifying which service it will use, the injector tells the client what service to use. The “injection” refers to the passing of a dependency (a service) into the object (a client) that would use it.

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Substitutability is a principle in object-oriented programming stating that, in a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e. an object of type T may be substituted with any object of a subtype S) without altering any of the desirable properties of the program (correctness, task performed, etc.). More formally, the Liskov substitution principle (LSP) is a particular definition of a subtyping relation, called (strongbehavioral subtyping, that was initially introduced by Barbara Liskov in a 1987.

The Liskov Substitution Principle is the third of Robert C. Martin’s SOLID design principles. It extends the Open/Closed principle and enables you to replace objects of a parent class with objects of a subclass without breaking the application. This requires all subclasses to behave in the same way as the parent class.


Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it.” – Robert C. Martin

A violation of this behaviour would imply your code is not SOLID and it may be prone to malfunctioning.

Listening to EXOplayer events

Kotlin 2020 solution approach UPDATE

Events such as changes in state and playback errors are reported to registered Player.EventListener instances.

Player.EventListener has empty default methods, so you only need to implement the methods you’re interested in.

First your class, say your activity, has te conform to the Player.EventListener interface.

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kotlinx.serialization library, the chosen one

It seems clear today that kotlinx.serialization is the chosen one.

Among all the many libraries to parse JSON with Kotlin in Android. Say… Klaxon, Jackson, Gson, Json2kotlin, etc. kotlinx.serialization is presently attested champion.

There’s no doubt kotlinx.serialization is the future as it is part of Kotlin libraries now. Although it is still at the time of writing this post in incubator stage.

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