Background View Rendering

MainActivity.kt

package com.ozodrukh.pictureexploration

import android.content.Context
import android.graphics.BitmapFactory
import android.graphics.Canvas
import android.graphics.Picture
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.view.View
import java.util.*
import java.util.concurrent.Executors
import java.util.concurrent.TimeUnit

class MainActivity : AppCompatActivity() {

  private lateinit var surface: PictureView

  private val ioExecutor = Executors.newScheduledThreadPool(1)
  private val picture = Picture()

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    surface = PictureView(this)
    setContentView(surface)

    val random = Random()

    ioExecutor.scheduleAtFixedRate ({
      val imageId: Int = when(random.nextInt(2)){
        0 -> R.drawable.image
        else -> R.drawable.image2
      }

      val bitmap = BitmapFactory.decodeResource(resources, imageId)

      val start = System.currentTimeMillis()
      val canvas = picture.beginRecording(300, 300)
      canvas.drawBitmap(bitmap, 0.0f, 0.0f, null)
      picture.endRecording()
      Log.i("PictureView", "record ended in ${System.currentTimeMillis() - start}")

      bitmap.recycle()

      runOnUiThread {
        surface.picture = picture
      }

    }, 0, 1, TimeUnit.SECONDS)
  }

  class PictureView(context: Context) : View(context) {

    internal var picture: Picture? = null
      set(value) {
        invalidate()
        field = value
      }

    override fun onDraw(canvas: Canvas) {
      super.onDraw(canvas)

      picture?.let {
        val start = System.currentTimeMillis()
        Log.i("PictureView", "drawing a picture")
        canvas.drawPicture(picture)
        Log.i("PictureView", "drawing a picture in ${System.currentTimeMillis() - start}")
      }
    }

  }
}