bitmap 保存到图片文件

val file = File(
    requireContext().getExternalFilesDir(Environment.DIRECTORY_PICTURES),
    "tmp_${System.currentTimeMillis()}.jpg"
)
val bos = BufferedOutputStream(FileOutputStream(file))
bitmap?.compress(Bitmap.CompressFormat.JPEG, 100, bos)
bos.flush()
bos.close()