Error Prevention

Error Prevention Comes First!

Before handling errors, you should first ask how errors can be prevented. Generally, you should design iViews and Web applications so that errors cannot occur. Preventing errors - instead of remedying them - has the following benefits:

• Users cannot come into error situations - many users have problems with recovering from errors.

• The users' work is not interrupted by error messages.

• Users are not confused or puzzled by (often cryptic) error messages.

• There is no need for a screen area that display errors.

If it is not possible to prevent errors, follow the guidelines presented in Error Handling for Fields .

How You can Prevent Errors

Often it needs some rethinking and the giving up "old habits" to find design solutions that prevent errors instead of sending an error message after an error has occurred.

In the following we provide some ideas and examples that may stimulate your imagination when looking for ways how errors can be prevented.

Prevent Wrong or Invalid Inputs - General

• Use precise descriptions and instructions - do not be too short (especially for Web applications)

• Indicate required fields (through a red asterisk *) and an explaining text

Prevent Wrong or Invalid Inputs

• Numeric fields: Prevent users from entering letters by parsing the input string.

• Date and time fields: Provide "intelligent" date and time fields that are preformatted, or provide selection controls instead of input fields (dropdown lists, spin buttons, calendar controls).

• Currency fields: Use preformatted fields.

Prevent Incomplete Inputs

• Indicate required fields (through a red asterisk *) and an explaining text

Prevent Invalid Actions

• Disable buttons that cannot be used in the current context.

• Do not offer functionality that is not needed.

Prevent Disastrous Actions

• If actions can have severe consequences for the user, add explaining texts to the respective buttons and inform the users about the consequences

• Send dialogs if users can loose data

Use Controls in the Correct and Intended Ways

• Do not use screen elements where uses expect to use them in any order, if there are dependencies or if a certain sequence of steps has to be followed.

  Example

  Do not use tabstrips for views that depend on each other and cannot be viewed at random. At best, do not force users to perform steps in a fixed sequence.

• In general, do not use controls in other than the intended ways. "Creative" use of controls clashes with the users' expectations and may lead to severe usage problems.

  Example

  Do not misuse checkboxes as radiobuttons just because you like the look of the checkboxes better.

Make the Page/iView and its Purpose Clear to the User

• Often important information is hidden while unimportant information dominates the page. In other cases users simply have no clue what an application's purpose is. Thus, provide the necessary information and arrange it so that relevant things are recognized first - this way users realize what to do on a screen and how.

• Use precise descriptions and instructions - do not be too short (especially for Web applications)