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