How can you find a file in a project (defined as everything under a single directory) using Icicles in Emacs? The feature I am looking for is similar to that offerred by the Projectile package.
The documentation mentions that this is possible, but says nothing on how to actually do it.
The reason I want to do this with Icicles instead of Projectile is that I want to use Icicles completion features and not Projectile's ido-like interface.
There are several ways to find a file among your project files. And the doc page you cite is the best place to start. Which ways you choose can depend on how you define a project as a collection of files.
If, as you say, you define your project files as all of those in and under a single directory (i.e., recursively), then these are some ways to do what you want:
Use command icicle-locate or icicle-locate-file for the project directory -- see Find Files Anywhere, Without Knowing Where
. You can cache the set of project file names for better performance -- see Persistent Completions.
Note that these commands, like all Icicles file-visiting commands, also let you search file contents -- match file name or contents or both. See Match File Names and File Content Too.
As @Aaron suggested, you can open Dired for your project main directory, and then use one of the Icicles commands for the contents of the marked files:
M-x M-s m (command icicles-search-dired-marked-recursive) -- it uses Icicles search.
M-+ C-F (command icicle-visit-marked-file-of-content-recursive) -- it visits marked files whose content matches a search pattern. (Again, see Match File Names and File Content Too.
Create bookmarks to Dired listings of your project directory. They can have different sets of files marked or omitted. If you use Bookmak+ then markings, omissions, and inserted subdirectories are all recorded as part of the bookmark.
Use Dired+ for even more possibilities -- synergy among Dired, Icicles and Bookmark+.
In particular, all of the things mentioned here, and more, are available from the Dired+ menus. (That will help you learn their keys.)
In particular, see submenu Marked Here and Below of menu-bar menu Multiple (which deals with marked files). It is the menu for acting on files anywhere below the current directory (no need to insert the subdirs etc.).