Drop-down menu for Emacs

When I am using yasnippet for a keyword that has more than one choices it opens up a new buffer instead of dropdown menu. How do I configure emacs to 开发者_运维技巧display a dropdown menu? Please see this cedet example for what I mean.

put yas-dropdown-prompt (or yas-x-prompt, if you want graphical menu like on cedet screenshots) at the first position in yas-prompt-functions variable, like this:

(require 'dropdown-list) ;; this is a separate package, that needs to be installed
(setq yas-prompt-functions
      '(yas-dropdown-prompt
        yas-ido-prompt
        yas-x-prompt
        yas-completing-prompt
        yas-no-prompt))