8 Input handling

Input can come from various sources, for example, from the user, a sync operation or a resource file. All input must be handled correctly to make sure it follows the constraints for the given situation and does not lead to strange or unexpected results.

The application should give notification when the user attempts to enter a value that is out-of-bounds or incorrect in some other way.

The application must be able to handle invalid input values.

The application should use Unicode characters by default.

Unprintable characters should be removed from list views, but kept in edit views if it is possible to enter them.

If an input string is entered to be used as a filename, no illegal characters are allowed. The illegal characters should not be removed automatically but instead the user should be notified. A complete path for a filename can not consist of more than 256 characters.

Strings used as filenames must not contain any illegal characters and must not consist of more than 256 characters.

Strings that do not fit on the screen should be wrapped or truncated. Truncations are followed by the Unicode character HORIZONTAL ELLIPSIS (U+2026).

Applications should be able to handle unusual key presses without panicking, that is, the application always ends up in a stable state.

Examples of unusual key presses and scenarios that should be handled:

• Activating the same icon or button repeatedly before the application has time to respond,

• Concurrent screen tap and confirmation key press,

• Closing a dialog before it has fully opened by tapping the Cancel button or by pressing the Back button,

• Long confirm presses.

The application should be able to handle unusual key presses without panicking.