Sensitivity

Sometimes it does not make sense to allow the user to interact with a control in the current context, for example, to press a Paste button when the clipboard is empty. At these times, make the control insensitive to minimize the risk of user error. While a control is insensitive, it will appear dimmed and will not be able to receive the focus, although assistive technologies like screenreaders will still be able to detect and report it.

It is usually better to make a control insensitive than to hide it altogether. This way, the user can learn about functionality they may be able to use later, even if it is not available right now.

Figure 6-1 Two check boxes: sensitive (top) and insensitive (bottom)

6.3.1. Locked Controls

In a network-managed environment, like a computer lab, system administrators usually want to "lock down" the values of certain settings, or remove them from the user interface altogether. This makes it easier for them to troubleshoot any problems that their users may encounter. In GNOME, the correct way for the system administrator to do this is by restricting write access to the GConf keys corresponding to those settings.

When you are designing your application, consider which settings a system administrator might want to make unavailable to users. These may typically include:

Settings that, if set wrongly, could prevent the application from functioning at all. For example, proxy settings in a network application.
Settings that could refer to networked resources. For example, the Templates directory in an office application, where shared stationery such as fax cover sheets might be stored.
Settings that customize the user interface, other than those required for accessibility. For example, certain menu, keyboard or toolbar customization options.

Your application needs to decide every time these controls are displayed whether or not they are available for editing, depending on the writeable state of the GConf key that holds its value. In the simplest case, your code for each control could look like that in the example below.

Example 6-1 Sample code fragment showing how to make a GConf-locked control insensitive

if (!gconf_key_is_writable (http_proxy))
        gtk_widget_set_sensitive (http_proxy_field, FALSE);

Include a section for system administrators in your user guide, explaining which settings they can lock, and their corresponding GConf keys.

Explain to the user why these controls cannot be edited at this time. You can do this with static text, tooltips or online help, depending on the situation. For example:

Figure 6-2 Example of a dialog with locked controls

Note that although they cannot be edited, the settings are still visible and selectable, and may be copied to the clipboard.

Sensitivity

6.3.1. Locked Controls

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