checkbox.go
func (c *CheckBox) SetAllow3State(enable bool) {
	if !enable && c.state == 2 {
		c.state = 0
	}
	c.allow3state = enable
}
func (c *CheckBox) SetAllow3State(enable bool) {
	if !enable && c.state == 2 {
		c.state = 0
	}
	c.allow3state = enable
}
// SetAllow3State sets if ComboBox should use 3 states. If the current
// state is unknown and one disables Allow3State option then the current
// value resets to off