Một trong những tính năng khả năng sử dụng tốt đẹp của một giao diện là người dùng có rất nhiều tính linh hoạt về nhiệm vụ trình tự. Đối với hầu hết các phần, tất cả các yếu tố trên màn hình có sẵn cho họ vào mọi lúc. Tuy nhiên, khi bạn tạo sử dụng các trường hợp và màn hình mockup của bạn, | 16 Chapter 13 Designing the Graphical User Interface If the user makes a mistake that can be caught immediately it is appropriate to give them some sort of instant feedback such as warning noise or a blinking element. Dialog Boxes One of the nice usability features of a GUI is that the user has a great deal of flexibility in terms of sequencing tasks. For the most part all elements on the screen are available to him or her at all times. However when you create your use-cases and your mockup screens you might run into situations that call for a strict sequence of events to take place. Counter to the normal GUI flexibility there will be times when for a particular action to take place you have to follow a fixed path. An obvious case is when the user chooses to save his or her work. When the save request is made no other work on the active project should take place until the save is either completed or abandoned. We use the term nonmodal to describe a GUI s typical openness. With a fixed-path situation like the save operation described above the term is not surprisingly modal. In the GUI world a modal sequence is one that can t be interrupted. We know you re familiar with the typical sequence of events when you go to save some work say a text document or perhaps a spreadsheet. When you make the save request the system typically displays a small window in the center of the screen known as a dialog box. Once the save file dialog box has been displayed no other application actions can take place until the dialog box has been dismissed. This locking out of other actions is called modal behavior. When you create a dialog box you have the choice to make it either modal or nonmodal. Always make it nonmodal as the default. However there are times when a dialog box really should be modal but use this only when absolutely necessary. Another good example of an appropriate use for a modal dialog box is when the user wants to open a network connection. Once the request is made no
