How does "Open With" some app in iPhone work?

As far as I know, from iOS SDK 3.2, file type handling is added and an iOS application can associate itself with some file type so that other applications can open this kind of file with the application.

Because of the sandbox mechanism in iOS, I wonder when a file in appA is opened with appB, which registered itself with this kind of file, what will happen? Is 开发者_如何学编程this file copied to appB and both appA and appB keep a copy of this file? If the answer is yes, is it possible to make appB open the file under appA's document folder? I cannot find any Apple documentation on this.

For example, appA stores a Keynote document in it, if I open this Keynote document with the Keynote app, is it possible to let Keynote app to edit this document in place so that after editing, appA can see the updated document?

Any help is appreciated.

There are a few different questions in here.

When you register your app to handle types of files using the info.plist entry Document types your app will be on the list of apps that are shown when you perform an action with that file (for example tapping a file attachment in an email). Then when your app is launched, the method application:didFinishLaunchingWithOptions: is run as normal, and the launchOptions dictionary will contain the path to the file that was sent to your app. What you do with the file from there is up to you, but it is a copy of the file, not a link to it. So if the user makes changes to the file in the original app they must 'launch' your app again, with the new file.

See here for more info: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIApplicationDelegate_Protocol/Reference/Reference.html#//apple_ref/occ/intfm/UIApplicationDelegate/application:didFinishLaunchingWithOptions:

You can't access any other app's document folder with the current SDK.

Also, for sharing documents in iTunes (like Pages, Numbers etc), look into the two info.plist entries Document types and UIFileSharingEnabled. (Apples docs: http://developer.apple.com/library/ios/#documentation/General/Reference/InfoPlistKeyReference/Articles/iPhoneOSKeys.html#//apple_ref/doc/uid/TP40009252-SW20) Basically, by setting UIFileSharingEnabled to YES you will expose the /Documents directory of your app in iTunes. Then again it's up to your to show the user once they are back in your app what's in that directory.

Sndbox implemented over standard unix permissions control. All applications are stored in folders with unique name (actually, GUIDs), however owner for them is the same mobile:mobile. So it looks like they just sends full file path to application which opens the corresponding file.