AndroidMediaSaver.kt

@Throws(IllegalStateException::class)
private fun saveImageToDisk(bitmap: Bitmap) {
	val fileName = "..."

	if (Build.VERSION.SDK_INT < 29) {
		val canWriteStorage =
			Build.VERSION.SDK_INT < 23 || checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED
		check(canWriteStorage) { "no storage permission" }

		val directory = pictureFolder
		checkNotNull(directory) { "no storage permission" }

		if (!directory.exists()) {
			directory.mkdirs()
		}
		check(directory.exists()) { "folder could not be_created" }			
		check(directory.canWrite()) { "dir $directory exists but is not writable" }

		val file = File(directory, fileName)
		FileOutputStream(file).use { outputStream ->
			bitmap.compress(Bitmap.CompressFormat.PNG, 100, outputStream)
		}
		addToGallery(file)
	} else {
		val contentValues = ContentValues()
		with(contentValues) {
			put(MediaStore.Images.Media.RELATIVE_PATH, Environment.DIRECTORY_PICTURES) // here you can add ' + "/" + subfolderName' to put the picture into a subfolder
			put(MediaStore.Images.Media.DISPLAY_NAME, fileName)
			put(MediaStore.Images.Media.MIME_TYPE, "image/png")
		}

		val imageUri: Uri? = contentResolver.insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, contentValues)
		checkNotNull(imageUri) { "Could not get an uri for $contentValues" }

		val outputStream = contentResolver.openOutputStream(imageUri)
		checkNotNull(outputStream) { "Could not get an OutputStream for uri $imageUri" }
		outputStream.use { bitmap.compress(Bitmap.CompressFormat.PNG, 100, it) }
	}
}


@SuppressLint("SdCardPath")
@Suppress("DEPRECATION") //
private val pictureFolder: File? = run {
	arrayOf(
		Environment.getExternalStorageDirectory(),
		File("/storage/emulated/$userNum/"),
		File("/storage/emulated/legacy/"),
		File("/data/media/$userNum"),
		File("/sdcard/")
	)
		.asSequence()
		.flatMap { f -> listOf(f.canonicalPath, f.absolutePath) }
		.firstOrNull { File(it).canWrite() }
		?.let { File(it, Environment.DIRECTORY_PICTURES) } // here you can add ' + "/" + subfolderName' to put the picture into a subfolder
}

private val userNum: Int = Process.myUid() / 100000

fun addToGallery(path: String) {
	MediaScannerConnection.scanFile(this, arrayOf(path), null, null)
}

fun addToGallery(file: File) {
	addToGallery(file.absolutePath)
}