docs/doxygen/overviews/validator.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        validator.h
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows licence
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_validator wxValidator Overview
  12
  13 Classes: wxValidator, wxTextValidator, wxGenericValidator
  14
  15 @li @ref overview_validator_intro
  16 @li @ref overview_validator_anatomy
  17 @li @ref overview_validator_dialogs
  18
  19
  20 <hr>
  21
  22
  23 @section overview_validator_intro Validator basic concepts
  24
  25 The aim of the validator concept is to make dialogs very much easier to write.
  26 A validator is an object that can be plugged into a control (such as a
  27 wxTextCtrl), and mediates between C++ data and the control, transferring the
  28 data in either direction and validating it. It also is able to intercept events
  29 generated by the control, providing filtering behaviour without the need to
  30 derive a new control class.
  31
  32 You can use a stock validator, such as wxTextValidator (which does text control
  33 data transfer, validation and filtering) and wxGenericValidator (which does
  34 data transfer for a range of controls); or you can write your own.
  35
  36 Here is an example of wxTextValidator usage.
  37
  38 @code
  39 wxTextCtrl *txt1 = new wxTextCtrl(
  40     this, -1, wxT(""), wxDefaultPosition, wxDefaultSize, 0,
  41     wxTextValidator(wxFILTER_ALPHA, &g_data.m_string));
  42 @endcode
  43
  44 In this example, the text validator object provides the following
  45 functionality:
  46
  47 @li It transfers the value of g_data.m_string (a wxString variable) to the
  48     wxTextCtrl when the dialog is initialised.
  49 @li It transfers the wxTextCtrl data back to this variable when the dialog is
  50     dismissed.
  51 @li It filters input characters so that only alphabetic characters are allowed.
  52
  53 The validation and filtering of input is accomplished in two ways. When a
  54 character is input, wxTextValidator checks the character against the allowed
  55 filter flag (@c wxFILTER_ALPHA in this case). If the character is inappropriate,
  56 it is vetoed (does not appear) and a warning beep sounds (unless
  57 wxValidator::SetBellOnError(false) has been called).
  58 The second type of validation is performed when the dialog is about to be dismissed,
  59 so if the default string contained invalid characters already, a dialog box is shown
  60 giving the error, and the dialog is not dismissed.
  61
  62 Note that any wxWindow may have a validator; using the @c wxWS_EX_VALIDATE_RECURSIVELY
  63 style (see wxWindow extended styles) you can also implement recursive validation.
  64
  65
  66 @section overview_validator_anatomy Anatomy of a Validator
  67
  68 A programmer creating a new validator class should provide the following
  69 functionality.
  70
  71 A validator constructor is responsible for allowing the programmer to specify
  72 the kind of validation required, and perhaps a pointer to a C++ variable that
  73 is used for storing the data for the control. If such a variable address is not
  74 supplied by the user, then the validator should store the data internally.
  75
  76 The wxValidator::Validate member function should return @true if the data in
  77 the control (not the C++ variable) is valid. It should also show an appropriate
  78 message if data was not valid.
  79
  80 The wxValidator::TransferToWindow member function should transfer the data from
  81 the validator or associated C++ variable to the control.
  82
  83 The wxValidator::TransferFromWindow member function should transfer the data
  84 from the control to the validator or associated C++ variable.
  85
  86 There should be a copy constructor, and a wxValidator::Clone function which
  87 returns a copy of the validator object. This is important because validators
  88 are passed by reference to window constructors, and must therefore be cloned
  89 internally.
  90
  91 You can optionally define event handlers for the validator, to implement
  92 filtering. These handlers will capture events before the control itself does
  93 (see @ref overview_events_processing).
  94 For an example implementation, see the @c valtext.h and @c valtext.cpp files in the
  95 wxWidgets library.
  96
  97
  98 @section overview_validator_dialogs How Validators Interact with Dialogs
  99
 100 For validators to work correctly, validator functions must be called at the
 101 right times during dialog initialisation and dismissal.
 102
 103 When a wxDialog::Show is called (for a modeless dialog) or wxDialog::ShowModal
 104 is called (for a modal dialog), the function wxWindow::InitDialog is
 105 automatically called. This in turn sends an initialisation event to the dialog.
 106 The default handler for the @c wxEVT_INIT_DIALOG event is defined in the wxWindow
 107 class to simply call the function wxWindow::TransferDataToWindow.
 108 This function finds all the validators in the window's children and calls the
 109 wxValidator::TransferToWindow function for each. Thus, data is transferred from C++
 110 variables to the dialog just as the dialog is being shown.
 111
 112 @note If you are using a window or panel instead of a dialog, you will need to
 113 call wxWindow::InitDialog explicitly before showing the window.
 114
 115 When the user clicks on a button, for example the OK button, the application
 116 should first call wxWindow::Validate, which returns @false if any of the child
 117 window validators failed to validate the window data. The button handler should
 118 return immediately if validation failed. Secondly, the application should call
 119 wxWindow::TransferDataFromWindow and return if this failed. It is then safe to
 120 end the dialog by calling wxDialog::EndModal (if modal) or wxDialog::Show (if modeless).
 121
 122 In fact, wxDialog contains a default command event handler for the @c wxID_OK
 123 button. It goes like this:
 124
 125 @code
 126 void wxDialog::OnOK(wxCommandEvent& event)
 127 {
 128     if ( Validate() && TransferDataFromWindow() )
 129     {
 130         if ( IsModal() )
 131             EndModal(wxID_OK);
 132         else
 133         {
 134             SetReturnCode(wxID_OK);
 135             this->Show(false);
 136         }
 137     }
 138 }
 139 @endcode
 140
 141 So if using validators and a normal OK button, you may not even need to write
 142 any code for handling dialog dismissal.
 143
 144 If you load your dialog from a resource file, you will need to iterate through
 145 the controls setting validators, since validators can't be specified in a
 146 dialog resource.
 147
 148 */
 149