1. A method for modifying a user-interface layer of an application executable by a data processing system having a display device and an input device without modifying the underlying functionality of the application, said method comprising: creating a task subclass for performing first and second functions in response to user input, said task subclass having one view interface; creating a view subclass having: a first user-interface layer for displaying first and second objects in a first window and for receiving user input from said first window; and a task interface for passing said user input from said first window to said task subclass via said view interface, such that said user input from said first window causes said task object to perform said first and second functions; and thereafter, modifying said view subclass by replacing said first user-interface layer with a second user-interface layer for displaying second and third windows, said second window containing said first object and not said second object and said third window containing said second object and not said first object, such that said application is modified to perform said first function in response to user input received from said second window and to perform said second function in response to user input received from said third window without said task subclass being modified.