How do I open a file with unknown associations in iOS?

I think it's rather impossible, but will ask anyway. My application uses file association to open some types of files. What I need is to make file associations within my app. For example I have some files in my app's Documents folder and when user wants to open that it would be a great idea to ask him in which application he would like it to 开发者_StackOverflow中文版open (like Mail app does).

It can possibly be done with URL schemes, but if I don't know what applications user has, it can't be used. So, is there any way to use the device's file associations within an application?

You should take a look at Document Interaction Programming Topics for iOS. It explains how you can use the UIDocumentInteractionController class to present the user a list of apps which support a given file.