Apple 2 manual Error Detection

C H A P T E R 6

Data Input

When a user initiates an action that can’t be undone and could be very difficult to reverse by hand, your application should warn the user and give the user a chance to cancel the action. For example, if a user is about to change a lot of text with a search-and-replace operation that can’t be undone, display a confirmation slip that says something to the effect of, “OK to make this change? (Can’t undo).”

Error Detection

Users may notice and correct some input errors, but your application should also check input items for validity. There are a couple of approaches you can take to error checking, depending on the circumstances and users’ expectations.

One approach is to check an input item for errors as soon as a user moves on to another input item. With this approach, a user must correct an error before the input gets stale or leads to other input errors. However, a user who makes lots of mistakes may feel pestered by what seem to be nitpicking error messages.

Another approach is to check all input items in one view at the same time, when a user taps a button to confirm all the input items and close the view. This approach only disrupts the user once per view instead of once per input item. If you take this approach, try to make your error messages as specific and diagnostic as possible. It’s all too easy to make error messages vague.

6-38 Error Handling