하고 싶은 일

화면 구현

app\src\main\res\layout\activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginLeft="24dp"
        android:layout_marginTop="24dp"
        android:text="フォトギャラリーを開く"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="130dp"
        android:layout_height="130dp"
        android:layout_marginTop="72dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btn"
        tools:srcCompat="@tools:sample/avatars" />

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="130dp"
        android:layout_height="130dp"
        android:layout_marginStart="32dp"
        android:layout_marginLeft="32dp"
        android:layout_marginTop="72dp"
        app:layout_constraintStart_toEndOf="@+id/imageView"
        app:layout_constraintTop_toBottomOf="@+id/btn"
        tools:srcCompat="@tools:sample/avatars" />

    <ImageView
        android:id="@+id/imageView3"
        android:layout_width="130dp"
        android:layout_height="130dp"
        android:layout_marginTop="32dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView"
        tools:srcCompat="@tools:sample/avatars" />

</androidx.constraintlayout.widget.ConstraintLayout>

메인 프로세싱 구현

MainActivity.kt

package com.example.yamato200604a

import android.content.Intent
import android.graphics.BitmapFactory
import android.net.Uri
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*

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

        // ボタン押下でフォトギャラリーを開く。
        val getButton = findViewById(R.id.btn) as Button
        getButton.setOnClickListener(object : View.OnClickListener {
            override
            fun onClick(view: View) {
                openPhotoGallery()
            }
        })
    }

    /**
     * Android端末のフォトギャラリー（写真を保存している内部フォルダ）を開く。
     * @author 大和賢一郎
     */
    private fun openPhotoGallery() {
        val intent = Intent(Intent.ACTION_OPEN_DOCUMENT)
        intent.type = "image/*"
        intent.putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true)
        intent.action = Intent.ACTION_PICK
        startActivityForResult(Intent.createChooser(intent, "Choose Photo"), CHOOSE_PHOTO_REQUEST_CODE)
    }

    companion object {
        private const val CHOOSE_PHOTO_REQUEST_CODE: Int = 43
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (requestCode == CHOOSE_PHOTO_REQUEST_CODE && resultCode == RESULT_OK) {
            val itemCount = data?.clipData?.itemCount ?: 0
            val uriList = mutableListOf<Uri>()
            for (i in 0..itemCount - 1) {
                val uri = data?.clipData?.getItemAt(i)?.uri
                uri?.let { uriList.add(it) }
            }

            val inputStream = contentResolver?.openInputStream(uriList[0])
            val image = BitmapFactory.decodeStream(inputStream)
            imageView.setImageBitmap(image)

            val inputStream2 = contentResolver?.openInputStream(uriList[1])
            val image2 = BitmapFactory.decodeStream(inputStream2)
            imageView2.setImageBitmap(image2)

            val inputStream3 = contentResolver?.openInputStream(uriList[2])
            val image3 = BitmapFactory.decodeStream(inputStream3)
            imageView3.setImageBitmap(image3)
        }
    }
}