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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