The QValidator class provides validation of input text, it is an abstract class. QIntValidator and QDoubleValidator inherit form QValidator and provide basic numeric-range checking. QRegularExpressionValidator provides general checking using a custom regular expression.

If the built-in validators are not sufficient you can subclass QValidator. The class has two virtual methods, validate() and fixup(). The validate() methods must be implemented by every subclass. It returns Invalid, Intermediate or Acceptable depending on whether its argument is valid for the subclass definition of valid.

Validation states

An Invalid string is clearly invalid.

Intermediate is less obvious. The concept of validity is difficult to apply when the string is incomplete (still being edited). QValidator defines Intermediate as the property of a string that is neither clearly invalid nor acceptable as a final result.

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 Intermediate.

• For a line edit which accepts integers from 10 to 1000 inclusive

  • 42 and 123 are Acceptable
  • an empty string and the number 5 are Intermediate
  • "asdf" and 1114 are both Invalid
   

• Given an editable combobox which accepts a URL

  • any well formed URL is Acceptable.
  • "http://example.com/," is Intermediate (user might be a cut and paste action that accidentally took in a comma at the end)
  • an empty string is Intermediate (user might select and delete all of the text in preparation for entering a new URL)
  • "http:///./" is Invalid
   

• Give a spin box which accepts lengths

  • "11cm" and "1in" are Acceptable
  • "11" and the empty string are Intermediate
  • "http://example.com" and "hour" are both Invalid

The fixup() method is provided for validators that can repair some user errors. The default implementation does nothing. QLineEdit, for example, will call fixup() if the user presses Enter (or Return) and the content is not currently valid. This allows the fixup() function the opportunity of performing some magic to make an Invalid string Acceptable.

A validator has a locale, set with setLocale(). It is typically used to parse localized data. For example, QIntValidator and QDoubleValidator use it to parse localized representations of integers and doubles.

QValidator is typically used with QLineEdit, QSpinBox and QComboBox.

See also

QIntValidator, QDoubleValidator, QRegularExpressionValidator