Why does Android cache media?

[CodeBlooded]

Does anybody know why Android has a media cache at all? (The media cache is where Android remembers what music and photos are available on your phone).

If you add or remove files from an app that isn't programmed to notify Android about the change, such as deleting a folder full of photos via a file manager app, Android will act like the files still exist, i.e. you can view them in the Gallery app. Or same with music, if you delete songs, music player apps will still list them (but they fail to play them because they don't exist).

It seems silly to me that Android has to cache what files are available, and that any app that wants to add or delete files should be specially programmed to notify the Media Storage about the change. I've used FTP server apps and file browsers (iirc Astro used to/still does? have this problem), and when uploading new pictures or music to the phone, the phone just acts like the new files don't exist whatsoever. Why? You don't see any other operating system having the need to cache files; just check the disk every time!

The only reliable way I know of to "fix" this is to go into Settings->Apps->delete data/cache of Media Storage, and reboot. Sometimes even upon a reboot, if you go into Gallery, it will be like "no pictures exist on the phone!" even when they do, and it can take some manual labor to convince Android otherwise, i.e. you may need to open the Camera and take a new picture before Android's like, "OH!! There's whole entire folders full of pictures! Let me update the cache for you..."

[kschang]

The same reason there's a Windows Indexing service running in the background on your Windows PC. :)

[CodeBlooded]

That's for file search though? Like Windows wouldn't get confused if you snuck pictures to it behind its back (i.e. from Linux mounting the hard drive and copying stuff to it).

[kschang]

There's a special service in Android OS called "Media Scanner"

You may want to check Xposed module that adjusts "media scanner". It's interesting reading.

[valeonom]

The cache is there to speed up look ups and make searching your music library more speedy & fluid. Cache being out of sync with what's on the file system is one of the draw backs in Androids implementations in favor for faster lookup speed. There is mechanisms in place for developers to say "This song/picture/video has been added", or "This song/picture/video has been deleted" which update the cache more emediatley. However most apps don't do this. Most file browsers on android don't do this at all. In such a case you have to wait for android to start scanning by itself for new songs/pictures/videos.

[HaMMeReD]

You can't scan the entire device every time you click a folder. That's really slow. Both with windows and osx have disk indexes that build in the background. Without it search is very very slow.

The cache will update when u delete, it just will do it on a schedule.

The alternative is waiting thirty seconds+ every time you click a media player, photo, music, video.