SharedPrefJson

package ドメイン.sharedprefjson

import android.content.Context

import android.content.SharedPreferences

import androidx.appcompat.app.AppCompatActivity

import android.os.Bundle

import android.view.View

import android.widget.Toast

import com.google.gson.Gson

import com.google.gson.reflect.TypeToken

import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    companion object {

        const val PREF_FILE_NAME = "record"

        const val PREF_SET_KEY = "scores"

    }

    private lateinit var preferences: SharedPreferences

    private val initBtnListener = View.OnClickListener {

        val scores = listOf(

            Score("Geri", 71),

            Score("Enoch", 82),

            Score("Pamela", 62),

            Score("Cornelius", 100),

            Score("Joanna", 59)

        )

        listView.adapter = ScoreAdapter(this, scores)

    }

    private val saveBtnListener = View.OnClickListener {

        val adapter = listView.adapter as ScoreAdapter

        val scores = adapter.scores

        // *** scores: List<Score> を JSON に変換 ***

        // Gson Instance 生成して、toJson() を呼んで Json を作成する

//        val json = Gson().toJson(scores)

        val json = scores.toJson()

        // SharedPreferences に保存する

        preferences.edit().putString(PREF_SET_KEY, json).apply()

        Toast.makeText(applicationContext, "保存しました", Toast.LENGTH_SHORT).show()

    }

    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)

        preferences = getSharedPreferences(PREF_FILE_NAME, Context.MODE_PRIVATE)

        btnInit.setOnClickListener(initBtnListener)

        btnSave.setOnClickListener(saveBtnListener)

        // SharedPreferences から読み込んでデータを表示させる

        showData()

    }

    private fun showData() {

        val data = preferences.getString(PREF_SET_KEY, null)

        if (data != null) {

//            val type = object : TypeToken<List<Score>>() {}.type

//            val scores = Gson().fromJson<List<Score>>(data, type)

//

//            listView.adapter = ScoreAdapter(this, scores)

            listView.adapter = ScoreAdapter(this, data.fromJson())

        }

    }

}

package ドメイン.sharedprefjson

import com.google.gson.Gson

import com.google.gson.reflect.TypeToken

data class Score(val name: String, val score: Int)

fun List<Score>.toJson(): String = Gson().toJson(this)

fun String.fromJson(): List<Score> =

    Gson().fromJson<List<Score>>(this, object : TypeToken<List<Score>>() {}.type)

package ドメイン.sharedprefjson

import android.content.Context

import android.view.LayoutInflater

import android.view.View

import android.view.ViewGroup

import android.widget.BaseAdapter

import android.widget.TextView

class ScoreAdapter(

    private val context: Context,

    val scores: List<Score>

) : BaseAdapter() {

    override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View =

        (convertView ?: createView(parent)).apply {

            val item = getItem(position)

            (tag as ViewHolder).run {

                name.text = item.name

                score.text = item.score.toString()

            }

        }

    override fun getItem(position: Int) = scores[position]

    override fun getItemId(position: Int) = position.toLong()

    override fun getCount() = scores.size

    private fun createView(parent: ViewGroup?) =

        LayoutInflater.from(context).inflate(R.layout.list_item_row, parent, false).apply {

            tag = ViewHolder(this)

        }

    class ViewHolder(view: View) {

        val name: TextView = view.findViewById(R.id.txtName)

        val score: TextView = view.findViewById(R.id.txtScore)

    }

}

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {

    …… 省略 ……

}

dependencies {

    …… 省略 ……

    def gson_version = "2.8.6"

    implementation "com.google.code.gson:gson:$gson_version"

}