 
 subsection3_3_3.html  subsection3_3_2.html  subsubsectionstar3_3_2_3.html  tableofcontents3_1.html   Next: subsection3_3_3.html Accessing The Components Up: subsection3_3_2.html Getting Started: the  Previous: subsubsectionstar3_3_2_3.html  Disabling Callbacks Temporarily    Validating User Inputs  
Sometimes it may be necessary to check the user input against certain
  criteria. For example, you may want to allow only even numbers in a
  TixControl widget. To do this, you can use the 
-validatecmd option,
  which specifies a Tcl command to call whenever the user enters a new
  value. Here is an example:
     tixControl .c -value 0 -step 2 -validatecmd evenOnly    proc evenOnly {value} {
        return [expr $value - ($value %2)]
    }
The value parameter to 
evenOnly is the new value entered by
  the user.  The 
evenOnly procedure makes sure that the new
  value is even by returning a modified, even number. The Tcl command
  specified by the 
-validatecmd must return a value which it
  deems valid and this value will be stored in the 
-value option
  of the TixControl widget.
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