1 question
iOS app is sandboxed, so if your app needs to open some file types in other apps, like dropbox app does, it could list the installed apps which could open specific types of file.
How can you do that?,
2 answer
You'll want to use UIDocumentInteractionController. See also the Document Interaction Programming Guide.
3 steps
Below is the detailed steps:
(For example, we have 2 apps)
App1 creates a file anywhere in its sandbox.
App1 calls docinteraction to display the "Open In" GUI for that file
User picks "Open in App2"
The iOS copies the file from one sandbox to the other and launches App2.
App2 implements didfinishlaunchingwithURL and loads the supplied URL (which is the copy in its sandbox)
1) http://stackoverflow.com/questions/7156932/open-file-in-another-app
2) http://stackoverflow.com/questions/4801590/ios-app-to-app-trasnmission-of-data-using-new-document-support-api
3) http://stackoverflow.com/questions/2774343/how-do-i-associate-file-types-with-an-iphone-application
4) http://apple.stackexchange.com/questions/25678/downloading-and-uploading-files-through-safari-ios