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1 \section{wxValidator overview}\label{validatoroverview}
2
3 Classes: \helpref{wxValidator}{wxvalidator}, \helpref{wxTextValidator}{wxtextvalidator},
4 \helpref{wxGenericValidator}{wxgenericvalidator}
5
6 The aim of the validator concept is to make dialogs very much easier to write.
7 A validator is an object that can be plugged into a control (such as a wxTextCtrl), and
8 mediates between C++ data and the control, transferring the data in either direction
9 and validating it. It also is able to intercept events generated
10 by the control, providing filtering behaviour without the need to derive a new control class.
11
12 You can use a stock validator, such as \helpref{wxTextValidator}{wxtextvalidator} (which does text
13 control data transfer, validation and filtering) and
14 \helpref{wxGenericValidator}{wxgenericvalidator} (which does data transfer for a range of controls);
15 or you can write your own.
16
17 \wxheading{Example}
18
19 Here is an example of wxTextValidator usage.
20
21 \begin{verbatim}
22 wxTextCtrl *txt1 = new wxTextCtrl(this, -1, wxT(""),
23 wxPoint(10, 10), wxSize(100, 80), 0,
24 wxTextValidator(wxFILTER_ALPHA, &g_data.m_string));
25 \end{verbatim}
26
27 In this example, the text validator object provides the following functionality:
28
29 \begin{enumerate}\itemsep=0pt
30 \item It transfers the value of g\_data.m\_string (a wxString variable) to the wxTextCtrl when
31 the dialog is initialised.
32 \item It transfers the wxTextCtrl data back to this variable when the dialog is dismissed.
33 \item It filters input characters so that only alphabetic characters are allowed.
34 \end{enumerate}
35
36 The validation and filtering of input is accomplished in two ways. When a character is input,
37 wxTextValidator checks the character against the allowed filter flag (wxFILTER\_ALPHA in this case). If
38 the character is inappropriate, it is vetoed (does not appear) and a warning beep sounds.
39 The second type of validation is performed when the dialog is about to be dismissed, so if
40 the default string contained invalid characters already, a dialog box is shown giving the
41 error, and the dialog is not dismissed.
42
43 \wxheading{Anatomy of a validator}
44
45 A programmer creating a new validator class should provide the following functionality.
46
47 A validator constructor is responsible for allowing the programmer to specify the kind
48 of validation required, and perhaps a pointer to a C++ variable that is used for storing the
49 data for the control. If such a variable address is not supplied by the user, then
50 the validator should store the data internally.
51
52 The \helpref{wxValidator::Validate}{wxvalidatorvalidate} member function should return
53 true if the data in the control (not the C++ variable) is valid. It should also show
54 an appropriate message if data was not valid.
55
56 The \helpref{wxValidator::TransferToWindow}{wxvalidatortransfertowindow} member function should
57 transfer the data from the validator or associated C++ variable to the control.
58
59 The \helpref{wxValidator::TransferFromWindow}{wxvalidatortransferfromwindow} member function should
60 transfer the data from the control to the validator or associated C++ variable.
61
62 There should be a copy constructor, and a \helpref{wxValidator::Clone}{wxvalidatorclone} function
63 which returns a copy of the validator object. This is important because validators
64 are passed by reference to window constructors, and must therefore be cloned internally.
65
66 You can optionally define event handlers for the validator, to implement filtering. These handlers
67 will capture events before the control itself does.
68
69 For an example implementation, see the valtext.h and valtext.cpp files in the wxWidgets library.
70
71 \wxheading{How validators interact with dialogs}
72
73 For validators to work correctly, validator functions must be called at the right times during
74 dialog initialisation and dismissal.
75
76 When a \helpref{wxDialog::Show}{wxdialogshow} is called (for a modeless dialog)
77 or \helpref{wxDialog::ShowModal}{wxdialogshowmodal} is called (for a modal dialog),
78 the function \helpref{wxWindow::InitDialog}{wxwindowinitdialog} is automatically called.
79 This in turn sends an initialisation event to the dialog. The default handler for
80 the wxEVT\_INIT\_DIALOG event is defined in the wxWindow class to simply call
81 the function \helpref{wxWindow::TransferDataToWindow}{wxwindowtransferdatatowindow}. This
82 function finds all the validators in the window's children and calls the TransferToWindow
83 function for each. Thus, data is transferred from C++ variables to the dialog
84 just as the dialog is being shown.
85
86 \normalbox{If you are using a window or panel instead of a dialog, you will need to
87 call \helpref{wxWindow::InitDialog}{wxwindowinitdialog} explicitly before showing the
88 window.}
89
90 When the user clicks on a button, for example the OK button, the application should
91 first call \helpref{wxWindow::Validate}{wxwindowvalidate}, which returns false if
92 any of the child window validators failed to validate the window data. The button handler
93 should return immediately if validation failed. Secondly, the application should
94 call \helpref{wxWindow::TransferDataFromWindow}{wxwindowtransferdatafromwindow} and
95 return if this failed. It is then safe to end the dialog by calling EndModal (if modal)
96 or Show (if modeless).
97
98 In fact, wxDialog contains a default command event handler for the wxID\_OK button. It goes like
99 this:
100
101 \begin{verbatim}
102 void wxDialog::OnOK(wxCommandEvent& event)
103 {
104 if ( Validate() && TransferDataFromWindow() )
105 {
106 if ( IsModal() )
107 EndModal(wxID_OK);
108 else
109 {
110 SetReturnCode(wxID_OK);
111 this->Show(false);
112 }
113 }
114 }
115 \end{verbatim}
116
117 So if using validators and a normal OK button, you may not even need to write any
118 code for handling dialog dismissal.
119
120 If you load your dialog from a resource file, you will need to iterate through the controls
121 setting validators, since validators can't be specified in a dialog resource.
122