7. design rules


Can you think of any instances in which the user control guideline suggested by Apple is not followed? (Hint: Think about the use of dialog boxes.)


The user control guideline states that, 'The user, not the computer, initiates and controls all actions.' In the case of dialog boxes, this guideline is clearly contradicted. A dialog box can be used to indicate when an error occurs in the system. Once this error has been detected and presented to the user in the dialog box, the only action that the system allows the user is to acknowledge the error and dismiss the dialog box. The system preempts the user dialog, with good reason. The preemptive nature of the dialog box is to ensure that the user actually notices that there was an error. Presumably, the only errors that will be produced in such an intrusive manner are ones which the user must know about before proceeding, so the preemption is warranted. But sometimes dialog boxes are not used to indicate errors and they still prevent the user from performing some actions that they might otherwise wish to perform. The dialog box might be asking the user to fill in some information to specify parameters for a command. If the user does not know what to provide, then they are stuck. A lot of the time, the user can find out the information by browsing through some other part of the system, but in order to do that they must exit the dialog box (and forfeit any of the settings that they might have already entered), find out the missing information and begin again. This kind of preemption is not desirable. It is probably this kind of preemption the user control guideline is intended to prevent, but it doesn't always get applied.

Other exercises in this chapter

ex.7.1 (ans), ex.7.2 (ans), ex.7.3 (open), ex.7.4 (ans), ex.7.5 (ans), ex.7.6 (ans), ex.7.7 (tut), ex.7.8 (tut), ex.7.9 (open)

all exercises for this chapter