Validator Overview

Validator basic concepts

The aim of the validator concept is to make dialogs very much easier to write. A validator is an object that can be plugged into a control (such as a wx.TextCtrl), and mediates between Python data and the control, transferring the data in either direction and validating it. It also is able to intercept events generated by the control, providing filtering behaviour without the need to derive a new control class.

wx.Validator can also be used to intercept keystrokes and other events within an input field. To use a validator, you have to create your own sub-class of wx.Validator (neither TextValidator nor GenericValidator are implemented in wxPython). This sub-class is then associated with your input field by calling:

myInputField.SetValidator(myValidator)

Note

Your wx.Validator sub-class must implement the wx.Validator.Clone method.

Note

Note that any wx.Window may have a validator; using the WS_EX_VALIDATE_RECURSIVELY style (see Window extended styles) you can also implement recursive validation.

Anatomy of a Validator

A programmer creating a new validator class should provide the following functionality.

A validator constructor is responsible for allowing the programmer to specify the kind of validation required, and perhaps a pointer to a Python variable that is used for storing the data for the control. If such a variable address is not supplied by the user, then the validator should store the data internally.

The wx.Validator.Validate method should return true if the data in the control (not the Python variable) is valid. It should also show an appropriate message if data was not valid.

The wx.Validator.TransferToWindow member function should transfer the data from the validator or associated Python variable to the control.

The wx.Validator.TransferFromWindow member function should transfer the data from the control to the validator or associated Python variable.

There should be a copy constructor, and a wx.Validator.Clone function which returns a copy of the validator object. This is important because validators are passed by reference to window constructors, and must therefore be cloned internally.

You can optionally define event handlers for the validator, to implement filtering. These handlers will capture events before the control itself does (see How Events are Processed).

How Validators Interact with Dialogs

For validators to work correctly, validator functions must be called at the right times during dialog initialisation and dismissal.

When a wx.Dialog.Show is called (for a modeless dialog) or wx.Dialog.ShowModal is called (for a modal dialog), the function wx.Window.InitDialog is automatically called. This in turn sends an initialisation event to the dialog. The default handler for the wxEVT_INIT_DIALOG event is defined in the wx.Window class to simply call the function wx.Window.TransferDataToWindow. This function finds all the validators in the window’s children and calls the wx.Validator.TransferToWindow function for each. Thus, data is transferred from Python variables to the dialog just as the dialog is being shown.

Note

If you are using a window or panel instead of a dialog, you will need to call wx.Window.InitDialog explicitly before showing the window.

When the user clicks on a button, for example the OK button, the application should first call wx.Window.Validate, which returns False if any of the child window validators failed to validate the window data. The button handler should return immediately if validation failed. Secondly, the application should call wx.Window.TransferDataFromWindow and return if this failed. It is then safe to end the dialog by calling wx.Dialog.EndModal (if modal) or wx.Dialog.Show (if modeless).

In fact, wx.Dialog contains a default command event handler for the ID_OK button. It goes like this:

def OnOK(self, event):

    if self.Validate() and self.TransferDataFromWindow():

        if self.IsModal():
            self.EndModal(wx.ID_OK)
        else:
            self.SetReturnCode(wx.ID_OK)
            self.Show(False)

So if using validators and a normal OK button, you may not even need to write any code for handling dialog dismissal.

If you load your dialog from a resource file, you will need to iterate through the controls setting validators, since validators can’t be specified in a dialog resource.