Android 画像一覧表示（遅い）

PhotoListActivity

package jp.paming.listsample

import android.Manifest
import android.content.ContentResolver
import android.content.ContentUris
import android.content.Context
import android.content.pm.PackageManager
import android.databinding.DataBindingUtil
import android.net.Uri
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.provider.MediaStore
import android.support.v4.app.ActivityCompat
import android.support.v4.content.ContextCompat
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.util.Log
import android.view.LayoutInflater
import android.view.ViewGroup
import android.widget.Toast
import jp.paming.listsample.databinding.RawPhotoBinding
import kotlinx.android.synthetic.main.activity_recycler.*
import java.util.*
import android.graphics.Bitmap



class PhotoListActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_photo_list)

        // Here, thisActivity is the current activity
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.READ_EXTERNAL_STORAGE)
            != PackageManager.PERMISSION_GRANTED) {

            // Should we show an explanation?
            if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                    Manifest.permission.READ_EXTERNAL_STORAGE)) {

                // Show an expanation to the user *asynchronously* -- don't block
                // this thread waiting for the user's response! After the user
                // sees the explanation, try again to request the permission.
                Toast.makeText(this, "パーミッションがOFFになっています。", Toast.LENGTH_SHORT).show();

            } else {

                // No explanation needed, we can request the permission.
                val permission = Manifest.permission.READ_EXTERNAL_STORAGE
                ActivityCompat.requestPermissions(this,
                    arrayOf(permission),
                    12345)

                // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
                // app-defined int constant. The callback method gets the
                // result of the request.
            }
        }else {
            val photoDataList = read()
            Log.d("photoDataList","${photoDataList}")

            recycleView.layoutManager = LinearLayoutManager(this)
            recycleView.adapter = PhotoListActivity.MyRecycleAdapter(this,
                contentResolver,
                photoDataList)

        }
    }

    // RecyclerView.ViewHolderを継承した自作ViewHolder
    // 親クラスの初期化にはBinding.rootで親Viewを渡し、
    // 子クラスはbindingを保持する
    class PhotoDataViewHolder(val binding: RawPhotoBinding) : RecyclerView.ViewHolder(binding.root)

    class MyRecycleAdapter(context: Context,val contentResolver:ContentResolver, val list:List<PhotoData>) : RecyclerView.Adapter<PhotoDataViewHolder>() {
        private val layoutInflater = LayoutInflater.from(context)

        override fun getItemCount(): Int {
            return list.size
        }

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): PhotoDataViewHolder {
            val binding: RawPhotoBinding = DataBindingUtil.inflate(layoutInflater,R.layout.raw_photo, parent, false)
            return PhotoDataViewHolder(binding)
        }

        override fun onBindViewHolder(holder: PhotoDataViewHolder, position: Int) {
            // ここではモデルに値をセットしている
            // →DataBindingにより、自動でViewに反映される
            holder.binding.date = list[position].dateString
            val bmp = MediaStore.Images.Media
                .getBitmap(contentResolver, list[position].uri)
            holder.binding.imageView.setImageBitmap(bmp)
        }
    }


    private fun read(): List<PhotoData> {
        //レコードの取得
//        var cursor = managedQuery(
//                MediaStore.Images.Media.EXTERNAL_CONTENT_URI, null, null, null,
//        null);
        val proj = arrayOf(
            MediaStore.Images.Media._ID,
            MediaStore.Images.Media.TITLE,
            MediaStore.Images.Media.DATA
            )

        val cursor = getContentResolver().query(
            MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
    //            MediaStore.Files.getContentUri("external"),
    //            proj,
            null,
            null,
            null,
            null
        ) ?: return emptyList()
        //        cursor.moveToFirst()

        Log.d("column","${cursor.columnCount}")
        for( i in (0 until cursor.columnCount) ){
            Log.d("column_name","${cursor.getColumnName(i)}")
        }
        Log.d("count", "${cursor.count}")

        val ret = ArrayList<PhotoData>()
        if (cursor.moveToFirst()){
            do {
                val id = cursor.getLong(cursor.getColumnIndex(MediaStore.Images.Media._ID))
                val added = cursor.getLong(cursor.getColumnIndex(MediaStore.Images.Media.DATE_ADDED))
                val date = Date(added)
                val bmpUri = ContentUris.withAppendedId(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, id);
                val photoData = PhotoData(bmpUri,date)
                ret.add(photoData)
            } while (cursor.moveToNext())
        }
        cursor.close()
        return ret
    }

}
class PhotoData(val uri:Uri, val date: Date){
    var dateString:String = ""
        get() = date.toString()
}