docs/latex/wx/tvalidat.tex

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