Moshi (converting array json to list of object) | deserialization in Kotlin

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Moshi (converting array json to list of object) | deserialization in Kotlin | Android Studio

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Moshi (converting array json to list of object) | deserialization in Kotlin | Android Studio

last updated: 29 November 2023

Converts json array. For example:

[
{"Name": "King of Trolles", "Price": 25 },
{"Name": "House", "Price": 100 }
]

And creates a list of objects. For example:

var books: List<MyBook>? = ConvertJsonToList(moshi, json)

Note!
The ConvertJsonToObject function does not need to be changed, it is template or generic.
In order to convert json text to a list of another type, you need to:

val moshi:Moshi = Moshi.Builder().build()

var jsonText1 = """ [
     {"Name": "King of Trolles", "Price": 25 },
     {"Name": "House", "Price": 100 }
     ] """
var books: List<MyBook>? = ConvertJsonToList(moshi, jsonText1)

val jsonText2 = """ [
     { "Location": "Street sunny", "Time": "12:43:15 PM" },
     { "Location": "Street Beverly Hils", "Time": "14:01:00 PM" }
     ] """
var films: List<MyFilm>? = ConvertJsonToList(moshi, jsonText2)

Step 1. Creating a new project

Create a new simple project "Empty Views Activity" on Kotlin in Android Studio ...

Step 2. Let's change the code in the file MainActivity.kt

My added code is filled in:

Kotlin File MainActivity.kt

package com.example.androidkotlinapp1

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.squareup.moshi.JsonAdapter
import com.squareup.moshi.JsonClass
import com.squareup.moshi.Moshi
import com.squareup.moshi.Types

@JsonClass(generateAdapter = true)
data class MyBook(
     val Name: String = "",
     val Price: Int = 0
)

inline fun <reified T> ConvertJsonToList(moshi:Moshi, jsonText:String): List<T>?
{
     val listType = Types.newParameterizedType(List::class.java, T::class.java)
     val moshiAdapter: JsonAdapter<List<T>> = moshi.adapter(listType)
     return moshiAdapter.fromJson(jsonText)
}

class MainActivity : AppCompatActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
          setContentView(R.layout.activity_main)

          // my functionality
          val moshi:Moshi = Moshi.Builder().build()

          try {
               var jsonText = """ [
               {"Name": "King of Trolles", "Price": 25 },
               {"Name": "House", "Price": 100 }
               ] """

               var books: List<MyBook>? = ConvertJsonToList(moshi, jsonText)

               books!!.forEach({
                    println("Book: ${it.Name.toString()} , ${it.Price.toString()}")
               })
          }
          catch (e:Exception)
          {
               println("Exception: ${e.message}")
          }
     }
}

Explanation:

Here is my class MyBook:

@JsonClass(generateAdapter = true)
data class MyBook(
val Name: String = "",
val Price: Int = 0
)

Description:
The @JsonClass attribute is needed for JSON conversion.

Since the class will only contain data without methods, I'll use the word data.
The word data means that the compiler for the class will add new members from the parameters in the constructor.

My ConvertJsonToList function converts the json array to a list of objects of type T and returns this list:

inline fun <reified T> ConvertJsonToList(moshi:Moshi, jsonText:String): List<T>?
{
     val listType = Types.newParameterizedType(List::class.java, T::class.java)
     val moshiAdapter: JsonAdapter<List<T>> = moshi.adapter(listType)
     return moshiAdapter.fromJson(jsonText)
}

Description:
My ConvertJsonToList function returns a list of unknown type T?.

At the beginning of the function, I specified inline <reified T>, which means that the function is template or generic, i.e. it will use an unknown type T.

Or you can do it like this:

~~inline~~ fun ~~<reified T>~~ <T> ConvertJsonToList(moshi:Moshi, jsonText:String): List<T>?

At the beginning of the function, I could specify <T>, which means that the function is also template or generic, i.e. it will use an unknown type T.

Why I'm using: inline <reified T>
Answer: That's the only way I can use T::class.java

var jsonText = """ [
{"Name": "King of Trolles", "Price": 25 },
{"Name": "House", "Price": 100 }
] """

The jsonText variable contains an array in the format json.

Note! I'm using """ to use the " character inside the text.

Step 3. Let's change the code in the file build.gradle

My added code is filled in:

File build.gradle

plugins {
     id 'com.android.application'
     id 'org.jetbrains.kotlin.android'
}

apply plugin: 'kotlin-kapt'

android {
     namespace 'com.example.androidkotlinapp1'
     compileSdk 33

     defaultConfig {
          applicationId "com.example.androidkotlinapp1"
          minSdk 27
          targetSdk 33
          versionCode 1
          versionName "1.0"

          testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
     }

     buildTypes {
          release {
               minifyEnabled false
               proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
          }
     }
     compileOptions {
          sourceCompatibility JavaVersion.VERSION_1_8
          targetCompatibility JavaVersion.VERSION_1_8
     }
     kotlinOptions {
          jvmTarget = '1.8'
     }
}

dependencies {
     implementation 'androidx.core:core-ktx:1.7.0'
     implementation 'androidx.appcompat:appcompat:1.6.1'
     implementation 'com.google.android.material:material:1.9.0'
     implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
     testImplementation 'junit:junit:4.13.2'
     androidTestImplementation 'androidx.test.ext:junit:1.1.5'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'

     // Moshi deserialization
     implementation 'com.squareup.moshi:moshi:1.14.0'
     kapt 'com.squareup.moshi:moshi-kotlin-codegen:1.14.0'
}

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Error "Failed to find the generated JsonAdapter class for class com.example.androidkotlinapp1.MyBook" | Exception | Kotlin | Moshi | Android Studio