More or less I use auto-complete field for a form. CJuiAutoComplete is a yii widget for this purposes.
The common use case is to make an ajax request and retrieve a list from the database. So in this case you have to write a controller action to return you a json encoded list.
What if I had a generic action to do this work for me?
In Yii, we can define an action class and ask the controller to instantiate it. And we always create ourselves actions class in rootPath/protected/extensions, and the view file we called in the actions class always are located in rootPath/protected/views/ControllerNAME or rootPath/themes/ThemeNAME/ControllerNAME, then when we use the same actions class in different controllers, we have to copy it from one controller to the other controller, so we also need the "same" view file work for us, here is an example.