For this project, we’re going to use a JSON file as a simple data source and write a program that rolls for the random results on the table defined in the JSON.

Setting Up a New Project

• File -> New -> New Project -> Empty Activity

Set Up the Project Structure

• src/main/java or src/main/kotlin: Root directory for our Kotlin source files.
  • com/ourapplicationname: Our application’s package.
    • data: Directory for data handling and network operations.
      • model: Contains model classes that represent the structure of our data. Our Kotlin class for the Model fits here.
      • repository: Contains repository classes that abstract the logic of data access and manipulation. They might interact with our model classes and data sources like databases, web services, or our JSON files.
    • ui: Directory for user interface related classes.
      • view: Contains activities, fragments, and any other views.
      • viewmodel: Contains ViewModel classes which hold the logic to manage the UI’s data in response to user actions.
    • util: Utility classes that provide common functionalities across the application.
• src/main/assets: Where we will keep data sources and other assets.

The JSON File

In the assets directory, I add lootTable.json that looks like this:

{
  "tableName": "Dungeon Loot Table",
  "description": "This table determines what loot you find in the dungeon.",
  "results": [
    "Gold coins",
    "Magic sword",
    "Potion of healing"
  ]
}

The Model

1. Set Up the Dependencies

We will use kotlinx to parse our JSON eventually, so we will have to edit the gradle files.

Under Gradle Scripts, there are two build.gradle.kts scripts. The one you want is marked with (Module :app).

Add the following to the existing sections:

plugins {  
id("org.jetbrains.kotlin.plugin.serialization") version "+"  
}

dependencies {  
implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:+")  
}

Be sure to sync the project when you’re done with editing this file.

Note that I use “+” when setting the version number. This will most often highlight in the editor with an option to use the latest version. You’ll notice when looking at a lot of online documentation (such as blogs like this) that they tend to list specific version numbers. You want the latest version though. So use this trick.

Also note that I use Kotlin syntax for my gradle files. Lots of online references will use groovy syntax.

2. Create the Model Class

In the data/model directory, I add the Kotlin class, LootTable.kt that looks like this:

package net.erickveil.mvi_table_roller.data.model  
import kotlinx.serialization.Serializable 

@Serializable
data class LootTable (  
	val tableName: String,  
	val description: String,  
	val results: List<String>  
)

In this model:

• @Serializable annotation is from kotlinx.serialization, indicating that this data class can be serialized and deserialized to and from JSON.
• LootTable is the main data class that represents our table, with properties matching the JSON keys: tableName, description, and results.
• tableName and description are of type String.
• results is a list of strings, each representing a possible outcome from the table.