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QValidator Class Reference


The QValidator class provides validation of input text. More...

#include <qvalidator.h>

Inherits QObject.

Inherited by QDoubleValidator and QIntValidator.

List of all member functions.

Public Members

Detailed Description

The QValidator class provides validation of input text.

The class itself is abstract; two subclasses provide rudimentary numeric range checking.

The class includes two virtual functions, validate() and fixup().

validate() is pure virtual, so it must be implemented by every subclass. It returns Invalid, Valid or Acceptable depending on whether its argument is valid (for the class' definition of valid).

The three states require some explanation. An Invalid string is clearly invalid. Valid is less obvious - the concept of validity is slippery when the string is incomplete (still being edited). QValidator defines Valid as the property of a string that it is not clearly invalid. Acceptable means that the string is acceptable as a final result. One might say that any string that is a plausible intermediate state during entry of an Acceptable string is Valid.

Here are some examples:

  1. For a line edit that accepts integers from 0 to 999 inclusive, 42 and 666 are Acceptable, the empty string and 1114 are Valid and asdf is Invalid.

  2. For an editable combo box that accepts URLs, any well-formed URL is Acceptable, "http://www.troll.no/," is Valid (it can be a cut-and-paste job that accidentally took in a comma at the end), the empty string is valid (the user might select and delete all of the text in preparation to entering a new URL), and "http:///./moron" is Invalid.

  3. For a spin box that accepts lengths, "11cm" and "1in" are Acceptable, "11" and the empty string are Valid, and "http://www.troll.no" and "hour" are Invalid.

    fixup() is provided for validators that can repair some or all user errors. The default does nothing. QLineEdit, for example, will call fixup() if the user presses Return and the content is not currently valid, in case fixup() can do magic. This allows some Invalid strings to be made Acceptable, too, spoiling the muddy definition above even more.

    QValidator is generally used with QLineEdit, QSpinBox and QComboBox.

    Member Function Documentation

    QValidator::QValidator ( QWidget * parent, const char * name = 0 )

    Sets up the internal data structures used by the validator. At the moment there aren't any.

    QValidator::~QValidator ()

    Deletes the validator and frees any storage and other resources used.

    void QValidator::fixup ( QString & input ) const [virtual]

    Attempts to change to be valid according to this validator's rules. Need not result in a valid string - callers of this function must re-test afterwards. The default does nothing.

    Reimplementation notes:

    Note that input may not be the only QString object referencing this string, so it's almost always necessary to detach() the string at the start of the code: 

        input.detach();

    You can change input even if you aren't able to produce a valid string. For example an ISBN validator might want to delete every character except digits and "-", even if the result is not a valid ISBN, and a last-name validator might want to remove white space from the start and end of the string, even if the resulting string is not in the list of known last names.

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    Qt version 2.0.2