Human-Computer Interaction 3e Dix, Finlay, Abowd, Beale

exercises  -  8. implementation support

EXERCISE 8.2

Look ahead to the example of the state transition diagram for font characteristics presented in Chapter 16 (Section 16.3.3). Compare different interaction objects that could implement this kind of dialog. Use examples from existing toolkits (pull-down menus or dialog boxes) or create a novel interaction object.

answer

In the example, we want to allow the user to toggle between three font characteristics - bold, italics and underline. Pull-down menus and dialog boxes are the most frequently used methods for implementing such a dialog. A pull-down menu would have the three choices listed with some way of indicating whether the characteristic was active or not. Upon each invocation of the menu, the user could change the active status of one font characteristic. For example, they could turn on the bold feature or turn off the underline feature. The important feature of this dialog is that more complex tasks (changing the active status of two or more font characteristics) can only be achieved by separate invocations of the menu. And often the only way the user can check the status would be by popping up the menu again (without invoking any action). This last point shows that the menu design alone does not support immediate display of relevant state changes as discussed in Chapter 7 under the synthesizability principle.

Within a dialog box, the user can effect several changes at one invocation. Technically, it is not the dialog box interaction device that allows for this, but the use of toggle buttons. Each font characteristic is represented by a box that acts as a simple on/off switch for that characteristic. As an aid to the user, the toggle button can change its appearance so that the user can know its status (on or off) by looking at it. A similar interaction widget is the checkbox, which would be labelled with the particular font characteristic. Clicking on the checkbox would put a mark in the box to indicate that the characteristic is on. Another click would remove the mark. In fact, a dialog box need not be used to portray the set of toggle buttons or checkboxes, as they could be presented continually so that the user can always view the current font characteristic settings. The reason a dialog box might be used is that there may be many font characteristics to choose from and the dialog box will keep them grouped together and preserve screen space by allowing them to be hidden and used on an as-needed basis.


Other exercises in this chapter

ex.8.1 (ans), ex.8.2 (ans), ex.8.3 (tut), ex.8.4 (tut), ex.8.5 (tut)

all exercises for this chapter


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