 
 section3_4.html  subsection3_3_5.html  subsubsection3_3_5_6.html  tableofcontents3_1.html   Next: section3_4.html Container Widgets Up: subsection3_3_5.html The TixSelect Widget  Previous: subsubsection3_3_5_6.html Accessing the Value    Specifying Complex Selection Rules  
If you want to have more complex selection rules for the
  TixSelect widget, you can use the 
-validatecmd option. This
  option works the same as the 
-validatecmd option of the
  TixControl widget which we discusses in section
  1.2: it specifies a command to be called every
  time the user attempts to change the selection inside a TixSelect
  widget.
In the example program 1-14, the procedure
  
TwoMax will be called every time the user tries to change the
  selection of the 
.fruits widget. TwoMax limits the
  maximum number of fruits that the user to choose to be 2 by always
  truncating the value of the TixSelect widget to have no more than
  two items. If you run this program, you will find out that you can
  never select a third fruit after you have select two fruits.
   tixSelect .fruits -label "Fruits: " -radio false -validatecmd TwoMax  .fruits add apple  -text Apple  -width 6
  .fruits add orange -text Orange -width 6
  .fruits add banana -text Banana -width 6
  pack .fruits
  proc TwoMax {value} {
     if {[llength $value] $>$ 2} {
        return [lrange $value 0 1]
     } else {
        return $value
     }
  }
(Figure 1-14) Specifying More Complex Selection Rules    
http://tix.sourceforge.nethttp://tix.sourceforge.net 