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In computing, a check box (checkbox, tickbox, or tick box) is a graphical user interface element (widget) that permits the user to make multiple selections from a number of options. Normally, check boxes are shown on the screen as a square box that can contain white space (for false) or a tick mark or X (for true), as pictured. Adjacent to the check box is normally shown a caption describing the meaning of the check box. Inverting the state of a check box is done by clicking the mouse on the box, or the caption, or by using a keyboard shortcut, such as the space bar.
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Tri-state check box
Some applications use a check box that allows three states rather than the two (selected and not selected) provided by a normal check box. This third state is shown by greying-out the checkbox (or, less often, displaying a dash in the checkbox). This can indicate that the box cannot be selected in the system's current state. Also, where a checkbox refers to a collection of objects, a greyed-out checkbox indicates that some objects in the collection test as true (checked) while others test false (empty). The greyed-out state cannot be selected by the user, but is a way of the checkbox reporting back to the user.
For example, a checkbox presented to select files to send via FTP might use a tree view so that files can be selected one at a time, or by selecting a folder, or sub-directory. If some files in a folder were checked and others were unchecked, then the checkbox for that folder would show as greyed out, because the files it contains are a mixture of selected and unselected. Clicking on this greyed-out checkbox would have one of two reactions, depending on the way it has been programmed; on repeated clicking these two states alternate, usually without returning to the greyed-out state:
- all sub-directories and sub-files (and the checkbox) would become checked
- all sub-directories and sub-files (and the checkbox) would become unchecked
Some tri-state check box implementations enable the user to toggle among all three states, including the mixed (gray) state by remembering the state of all the checkboxes in the collection. This serves as an undo feature.
HTML
In web forms, the HTML element <input type="checkbox" /> is used to display a check box.
Unicode
In Unicode, empty and filled check boxes are represented by code points U+2610 (☐, 'BALLOT BOX'), U+2611 (☑, 'BALLOT BOX WITH CHECK'), and U+2612 (☒, 'BALLOT BOX WITH X').
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See also
Wikipedia content modification information:
- This page was last modified on 4 December 2008, at 03:38.
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