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# widget_validator(n) 0.1 tklib "widget::validator behaviour"

## Name

widget_validator - widget::validator behaviour

## Synopsis

- package require Tcl 8.5
- package require Tk 8.5
- package require widget::validator ?0.1?

- widget::validator attach w color cmdprefix
- widget::validator detach w
- widget::validator validate w

## Description

This package provides a unified validation API for ttk's entry and combobox widgets.

Please note that the validation behaviour defined in this package will not reject invalid edits. It will only highlight the entry containing invalid data and set the proper state flag.

It is the responsibility of the using package or application to decide how and when to actually reject such invalid content.

widget::validator attach w color cmdprefix

  This method adds a validating behaviour to the widget w.

  Whenever the content of the widget's entry field changes the specified cmdprefix is invoked and has to return a boolean value, where true means that content is ok, and false that the content is invalid. For more information on the command prefix see section Validation. In case of the latter the background color of the entry field is changed to color to indicate the invalidity.

  The system does not support nesting of validators on a widget, nor the attachment of multiple validators. To change validating conditions detach the current validator first before attaching the new.

  An error is thrown if the widget has already validating behaviour attached to it.

  The result of the method is the empty string.

  To achieve its aims the package overrides various configuration options of the widget the behaviour is attached to. These options are restored to their previous values on detach.

  If other behaviours are attached the validator may be rendered temporarily (partially) non-functional. Similarly, if the validator is detached while a different behaviour is also attached its restoration of configuration settings may render the other non-functional

widget::validator detach w

  This method removes the validating behaviour from the widget w and restores it to its original state.

  An error is thrown if the widget has no validating behaviour attached to it.

  The result of the method is the empty string.

widget::validator validate w

  Invoking this method forces a validation of the widget w, assuming that it has a validator behaviour attached to it.

  The result of the method is the empty string.

## Validation

The command prefix for used for validation has to have the following signature:

{*}cmdprefix text

  The argument is the text to validate.

  The result of the callback has to be a boolean value where true means that text is ok, and false that text is invalid.

## Example

    package require Tk 8.5
    package require widget::validator
    set TE {}
    set TC {}
    ttk::entry    .e -textvariable TE
    ttk::combobox .c -textvariable TC -values {fruit vegetable corn}
    ttk::combobox .n -values {fruit vegetable corn}
    ttk::button   .x -command ::exit -text Exit
    pack .e -expand 1 -fill both -side top
    pack .c -expand 1 -fill both -side top
    pack .n -expand 1 -fill both -side top
    pack .x -expand 1 -fill both -side top
    widget::validator attach .e lightblue {apply {text {
        expr {$text ne {}}
    }}}
    widget::validator attach .c yellow {apply {text {
        expr {$text ni {{} hello world}}
    }}}
    widget::validator attach .n pink {apply {text {
        expr {$text ni {{} blub}}
    }}}

## Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category widget::validator of the Tklib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

## Keywords

invalid, state management, ttk::combobox, ttk::entry, validation, widget validation