docs/doxygen/overviews/validator.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        validator
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /*!
  10
  11  @page overview_validator wxValidator overview
  12
  13  Classes: #wxValidator, #wxTextValidator,
  14  #wxGenericValidator
  15  The aim of the validator concept is to make dialogs very much easier to write.
  16  A validator is an object that can be plugged into a control (such as a wxTextCtrl), and
  17  mediates between C++ data and the control, transferring the data in either direction
  18  and validating it. It also is able to intercept events generated
  19  by the control, providing filtering behaviour without the need to derive a new control class.
  20  You can use a stock validator, such as #wxTextValidator (which does text
  21  control data transfer, validation and filtering) and
  22  #wxGenericValidator (which does data transfer for a range of controls);
  23  or you can write your own.
  24  @b Example
  25  Here is an example of wxTextValidator usage.
  26
  27  @code
  28  wxTextCtrl *txt1 = new wxTextCtrl(this, -1, wxT(""),
  29      wxPoint(10, 10), wxSize(100, 80), 0,
  30      wxTextValidator(wxFILTER_ALPHA, _data.m_string));
  31  @endcode
  32
  33  In this example, the text validator object provides the following functionality:
  34
  35
  36   It transfers the value of g_data.m_string (a wxString variable) to the wxTextCtrl when
  37  the dialog is initialised.
  38   It transfers the wxTextCtrl data back to this variable when the dialog is dismissed.
  39   It filters input characters so that only alphabetic characters are allowed.
  40
  41
  42  The validation and filtering of input is accomplished in two ways. When a character is input,
  43  wxTextValidator checks the character against the allowed filter flag (wxFILTER_ALPHA in this case). If
  44  the character is inappropriate, it is vetoed (does not appear) and a warning beep sounds.
  45  The second type of validation is performed when the dialog is about to be dismissed, so if
  46  the default string contained invalid characters already, a dialog box is shown giving the
  47  error, and the dialog is not dismissed.
  48  @b Anatomy of a validator
  49  A programmer creating a new validator class should provide the following functionality.
  50  A validator constructor is responsible for allowing the programmer to specify the kind
  51  of validation required, and perhaps a pointer to a C++ variable that is used for storing the
  52  data for the control. If such a variable address is not supplied by the user, then
  53  the validator should store the data internally.
  54  The wxValidator::Validate member function should return
  55  @true if the data in the control (not the C++ variable) is valid. It should also show
  56  an appropriate message if data was not valid.
  57  The wxValidator::TransferToWindow member function should
  58  transfer the data from the validator or associated C++ variable to the control.
  59  The wxValidator::TransferFromWindow member function should
  60  transfer the data from the control to the validator or associated C++ variable.
  61  There should be a copy constructor, and a wxValidator::Clone function
  62  which returns a copy of the validator object. This is important because validators
  63  are passed by reference to window constructors, and must therefore be cloned internally.
  64  You can optionally define event handlers for the validator, to implement filtering. These handlers
  65  will capture events before the control itself does.
  66  For an example implementation, see the valtext.h and valtext.cpp files in the wxWidgets library.
  67  @b How validators interact with dialogs
  68  For validators to work correctly, validator functions must be called at the right times during
  69  dialog initialisation and dismissal.
  70  When a wxDialog::Show is called (for a modeless dialog)
  71  or wxDialog::ShowModal is called (for a modal dialog),
  72  the function wxWindow::InitDialog is automatically called.
  73  This in turn sends an initialisation event to the dialog. The default handler for
  74  the wxEVT_INIT_DIALOG event is defined in the wxWindow class to simply call
  75  the function wxWindow::TransferDataToWindow. This
  76  function finds all the validators in the window's children and calls the TransferToWindow
  77  function for each. Thus, data is transferred from C++ variables to the dialog
  78  just as the dialog is being shown.
  79
  80  If you are using a window or panel instead of a dialog, you will need to
  81  call wxWindow::InitDialog explicitly before showing the
  82  window.
  83
  84  When the user clicks on a button, for example the OK button, the application should
  85  first call wxWindow::Validate, which returns @false if
  86  any of the child window validators failed to validate the window data. The button handler
  87  should return immediately if validation failed. Secondly, the application should
  88  call wxWindow::TransferDataFromWindow and
  89  return if this failed. It is then safe to end the dialog by calling EndModal (if modal)
  90  or Show (if modeless).
  91  In fact, wxDialog contains a default command event handler for the wxID_OK button. It goes like
  92  this:
  93
  94  @code
  95  void wxDialog::OnOK(wxCommandEvent& event)
  96  {
  97      if ( Validate() && TransferDataFromWindow() )
  98      {
  99          if ( IsModal() )
 100              EndModal(wxID_OK);
 101          else
 102          {
 103              SetReturnCode(wxID_OK);
 104              this-Show(@false);
 105          }
 106      }
 107  }
 108  @endcode
 109
 110  So if using validators and a normal OK button, you may not even need to write any
 111  code for handling dialog dismissal.
 112  If you load your dialog from a resource file, you will need to iterate through the controls
 113  setting validators, since validators can't be specified in a dialog resource.
 114
 115  */
 116
 117