Permission to read another app's data?

Is there a permission to allow one app to read the (private) data/data//files/开发者_开发问答... files of another application? If not, how do backup programs like MyBackup work?

C

On a side-note, in the unlikely event that you're the one who's writing both applications, you can make them share the same sandbox by signing them the same way.

Is there a permission to allow one app to read the (private) data/data//files/... files of another application?

No.

If not, how do backup programs like MyBackup work?

They backup and restore only things with public APIs. That includes some data from the operating system and some things from applications specifically integrated with them.