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 license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /*!
  10
  11 @page overview_validator wxValidator Overview
  12
  13 Classes: wxValidator, wxTextValidator, wxGenericValidator
  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
  27 @li @ref overview_validator_example
  28 @li @ref overview_validator_anatomy
  29 @li @ref overview_validator_dialogs
  30
  31
  32 <hr>
  33
  34
  35 @section overview_validator_example Example
  36
  37 Here is an example of wxTextValidator usage.
  38
  39 @code
  40 wxTextCtrl *txt1 = new wxTextCtrl(
  41     this, -1, wxT(""), wxPoint(10, 10), wxSize(100, 80), 0,
  42     wxTextValidator(wxFILTER_ALPHA, &g_data.m_string));
  43 @endcode
  44
  45 In this example, the text validator object provides the following
  46 functionality:
  47
  48 @li It transfers the value of g_data.m_string (a wxString variable) to the
  49     wxTextCtrl when the dialog is initialised.
  50 @li It transfers the wxTextCtrl data back to this variable when the dialog is
  51     dismissed.
  52 @li It filters input characters so that only alphabetic characters are allowed.
  53
  54 The validation and filtering of input is accomplished in two ways. When a
  55 character is input, wxTextValidator checks the character against the allowed
  56 filter flag (wxFILTER_ALPHA in this case). If the character is inappropriate,
  57 it is vetoed (does not appear) and a warning beep sounds. The second type of
  58 validation is performed when the dialog is about to be dismissed, so if the
  59 default string contained invalid characters already, a dialog box is shown
  60 giving the error, and the dialog is not dismissed.
  61
  62
  63 @section overview_validator_anatomy Anatomy of a Validator
  64
  65 A programmer creating a new validator class should provide the following
  66 functionality.
  67
  68 A validator constructor is responsible for allowing the programmer to specify
  69 the kind of validation required, and perhaps a pointer to a C++ variable that
  70 is used for storing the data for the control. If such a variable address is not
  71 supplied by the user, then the validator should store the data internally.
  72
  73 The wxValidator::Validate member function should return @true if the data in
  74 the control (not the C++ variable) is valid. It should also show an appropriate
  75 message if data was not valid.
  76
  77 The wxValidator::TransferToWindow member function should transfer the data from
  78 the validator or associated C++ variable to the control.
  79
  80 The wxValidator::TransferFromWindow member function should transfer the data
  81 from the control to the validator or associated C++ variable.
  82
  83 There should be a copy constructor, and a wxValidator::Clone function which
  84 returns a copy of the validator object. This is important because validators
  85 are passed by reference to window constructors, and must therefore be cloned
  86 internally.
  87
  88 You can optionally define event handlers for the validator, to implement
  89 filtering. These handlers will capture events before the control itself does.
  90 For an example implementation, see the valtext.h and valtext.cpp files in the
  91 wxWidgets library.
  92
  93
  94 @section overview_validator_dialogs How Validators Interact with Dialogs
  95
  96 For validators to work correctly, validator functions must be called at the
  97 right times during dialog initialisation and dismissal.
  98
  99 When a wxDialog::Show is called (for a modeless dialog) or wxDialog::ShowModal
 100 is called (for a modal dialog), the function wxWindow::InitDialog is
 101 automatically called. This in turn sends an initialisation event to the dialog.
 102 The default handler for the wxEVT_INIT_DIALOG event is defined in the wxWindow
 103 class to simply call the function wxWindow::TransferDataToWindow. This function
 104 finds all the validators in the window's children and calls the
 105 TransferToWindow function for each. Thus, data is transferred from C++
 106 variables to the dialog just as the dialog is being shown.
 107
 108 @note If you are using a window or panel instead of a dialog, you will need to
 109 call wxWindow::InitDialog explicitly before showing the window.
 110
 111 When the user clicks on a button, for example the OK button, the application
 112 should first call wxWindow::Validate, which returns @false if any of the child
 113 window validators failed to validate the window data. The button handler should
 114 return immediately if validation failed. Secondly, the application should call
 115 wxWindow::TransferDataFromWindow and return if this failed. It is then safe to
 116 end the dialog by calling EndModal (if modal) or Show (if modeless).
 117
 118 In fact, wxDialog contains a default command event handler for the wxID_OK
 119 button. It goes like this:
 120
 121 @code
 122 void wxDialog::OnOK(wxCommandEvent& event)
 123 {
 124     if ( Validate() && TransferDataFromWindow() )
 125     {
 126         if ( IsModal() )
 127             EndModal(wxID_OK);
 128         else
 129         {
 130             SetReturnCode(wxID_OK);
 131             this->Show(false);
 132         }
 133     }
 134 }
 135 @endcode
 136
 137 So if using validators and a normal OK button, you may not even need to write
 138 any code for handling dialog dismissal.
 139
 140 If you load your dialog from a resource file, you will need to iterate through
 141 the controls setting validators, since validators can't be specified in a
 142 dialog resource.
 143
 144 */
 145