This action takes after the action "Open Classes" to help the user open any file in the current project.
If the current project does not have any "Directory View" set up, the action will scan ALL the files under the project directory. (In the future it can be changed to skip the output directory and backup directory).
This is to let the user customize the scanning area, by setting up the directory view. When there are directory views set up in the project, only the files viewable under those nodes will be scanned. In this way, the user can skip certain directories, as well as adding directories that are outside the project. (Since DiretoryView was not implemented with this action in sight, the idea can be unnatural.)