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
  16  The aim of the validator concept is to make dialogs very much easier to write.
  17  A validator is an object that can be plugged into a control (such as a wxTextCtrl), and
  18  mediates between C++ data and the control, transferring the data in either direction
  19  and validating it. It also is able to intercept events generated
  20  by the control, providing filtering behaviour without the need to derive a new control class.
  21
  22  You can use a stock validator, such as #wxTextValidator (which does text
  23  control data transfer, validation and filtering) and
  24  #wxGenericValidator (which does data transfer for a range of controls);
  25  or you can write your own.
  26
  27  @section example Example
  28
  29  Here is an example of wxTextValidator usage.
  30
  31  @code
  32  wxTextCtrl *txt1 = new wxTextCtrl(this, -1, wxT(""),
  33      wxPoint(10, 10), wxSize(100, 80), 0,
  34      wxTextValidator(wxFILTER_ALPHA, _data.m_string));
  35  @endcode
  36
  37  In this example, the text validator object provides the following functionality:
  38
  39  @li It transfers the value of g_data.m_string (a wxString variable) to the wxTextCtrl when
  40  the dialog is initialised.
  41  @li It transfers the wxTextCtrl data back to this variable when the dialog is dismissed.
  42  @li It filters input characters so that only alphabetic characters are allowed.
  43
  44  The validation and filtering of input is accomplished in two ways. When a character is input,
  45  wxTextValidator checks the character against the allowed filter flag (wxFILTER_ALPHA in this case). If
  46  the character is inappropriate, it is vetoed (does not appear) and a warning beep sounds.
  47  The second type of validation is performed when the dialog is about to be dismissed, so if
  48  the default string contained invalid characters already, a dialog box is shown giving the
  49  error, and the dialog is not dismissed.
  50
  51  @section anatomy Anatomy of a validator
  52
  53  A programmer creating a new validator class should provide the following functionality.
  54
  55  A validator constructor is responsible for allowing the programmer to specify the kind
  56  of validation required, and perhaps a pointer to a C++ variable that is used for storing the
  57  data for the control. If such a variable address is not supplied by the user, then
  58  the validator should store the data internally.
  59
  60  The wxValidator::Validate member function should return
  61  @true if the data in the control (not the C++ variable) is valid. It should also show
  62  an appropriate message if data was not valid.
  63
  64  The wxValidator::TransferToWindow member function should
  65  transfer the data from the validator or associated C++ variable to the control.
  66
  67  The wxValidator::TransferFromWindow member function should
  68  transfer the data from the control to the validator or associated C++ variable.
  69
  70  There should be a copy constructor, and a wxValidator::Clone function
  71  which returns a copy of the validator object. This is important because validators
  72  are passed by reference to window constructors, and must therefore be cloned internally.
  73
  74  You can optionally define event handlers for the validator, to implement filtering. These handlers
  75  will capture events before the control itself does.
  76  For an example implementation, see the valtext.h and valtext.cpp files in the wxWidgets library.
  77
  78  @section dialogs How validators interact with dialogs
  79
  80  For validators to work correctly, validator functions must be called at the right times during
  81  dialog initialisation and dismissal.
  82
  83  When a wxDialog::Show is called (for a modeless dialog)
  84  or wxDialog::ShowModal is called (for a modal dialog),
  85  the function wxWindow::InitDialog is automatically called.
  86  This in turn sends an initialisation event to the dialog. The default handler for
  87  the wxEVT_INIT_DIALOG event is defined in the wxWindow class to simply call
  88  the function wxWindow::TransferDataToWindow. This
  89  function finds all the validators in the window's children and calls the TransferToWindow
  90  function for each. Thus, data is transferred from C++ variables to the dialog
  91  just as the dialog is being shown.
  92
  93  @note If you are using a window or panel instead of a dialog, you will need to
  94  call wxWindow::InitDialog explicitly before showing the
  95  window.
  96
  97  When the user clicks on a button, for example the OK button, the application should
  98  first call wxWindow::Validate, which returns @false if
  99  any of the child window validators failed to validate the window data. The button handler
 100  should return immediately if validation failed. Secondly, the application should
 101  call wxWindow::TransferDataFromWindow and
 102  return if this failed. It is then safe to end the dialog by calling EndModal (if modal)
 103  or Show (if modeless).
 104
 105  In fact, wxDialog contains a default command event handler for the wxID_OK button. It goes like
 106  this:
 107
 108  @code
 109  void wxDialog::OnOK(wxCommandEvent& event)
 110  {
 111      if ( Validate() && TransferDataFromWindow() )
 112      {
 113          if ( IsModal() )
 114              EndModal(wxID_OK);
 115          else
 116          {
 117              SetReturnCode(wxID_OK);
 118              this-Show(@false);
 119          }
 120      }
 121  }
 122  @endcode
 123
 124  So if using validators and a normal OK button, you may not even need to write any
 125  code for handling dialog dismissal.
 126
 127  If you load your dialog from a resource file, you will need to iterate through the controls
 128  setting validators, since validators can't be specified in a dialog resource.
 129
 130  */
 131
 132