Contract
Parameter key	Default value	Type
name	opt	string
label	null	string
x	active_value	nonnegative
y	active_value	nonnegative
width	active_value	nonnegative
height	active_value	nonnegative
foreground_color	black	color
background_color	white	color
visibility	active_value	boolean
tool_tip	null	type.<one_of string/>
the_value	active_value	boolean
click	opt	method

Water Contract
<class ui.item.checkbox name =opt=string label =null=string the_value =<active_value></active_value>=boolean click =opt=method />

See also: radiobutton

Checkbox displays its label next to a small rectangle. When the user clicks on it, the checkbox will toggle between checked and unchecked. the_value is set to the new value of the checkbox with 'true' meaning checked and 'false' meaning unchecked. Then the click method is called with the checkbox clicked on as the subject of the call. The default value of the_value is false indicating an unchecked state, but the_value can be initialized during button creation to 'true' if you like. the_value can also be read and set programmatically using get (or the dot syntax) and the 'set' method.

ui.<window name="mywin">
 null
 ui.<row>
  ui.<checkbox name="check0" click=<method null> <echo "the_value is " _subject.the_value/></>/>
  ui.<checkbox name="check1" the_value=true/>
 </row>
</window>
ui.mywin.center.1.<set the_value=false/> <!-- programmatically set the value -->
ui.mywin.center.1.the_value              <!-- returns false -->

Note that check1 in the above example doesn't have a click method. That's fine. Often check boxes are just read by the program when the program is ready to read them. If you want some action to happen as soon as the user clicks on the checkbox, give the checkbox a click method.