CFilterEdit: Use Regular Expressions to Filter Your Input

• Download source files - 28.99 KB
• Download demo project - 46.13 KB

 

 

Introduction

Ever since computers were invented, data validation has been an important concern. When it comes to a user interface, the fastest way to validate data is whilst it is being input. Strange, then, that there is no standard Windows edit control that tackles this problem for any kind of data.

This validating edit control aims to provide the ultimate Framework for data validation, no matter how complex the data you are attempting to input is.

Design Decisions

• Validation must be clean and reliable
• The control should be usable exactly like CEdit
• Only a handful of visual effects will be included as standard
• 'WM_KILLFOCUS is the wrong time to do field validation'
• Auto-formatting should be easy to add from a derived class
• FilterEdit must stay as simple as possible and not get too bloated!

Intercepted Windows Messages

The following Windows messages are trapped for validation purposes:

• EM_REPLACESEL
• WM_CLEAR
• WM_CHAR
• WM_CUT
• WM_KEYDOWN
• WM_KEYUP
• WM_KILLFOCUS
• WM_PASTE
• WM_SETFOCUS
• WM_SETTEXT

... and these are trapped to perform the visual effects:

• WM_CTLCOLOR
• WM_PAINT

Windows Message Overrides for Validation

CBaseEdit::OnChar

WM_CHAR is the Windows message that every validating edit control ever written for Windows must have trapped. This is where a single character can be checked to see if the control will accept it or not.

CBaseEdit::OnKeyDown

WM_KEYDOWN is where the Delete key, Ctrl-X, Ctrl-C and Ctrl-V are trapped.

CBaseEdit::OnKillFocus

Again, WM_KILLFOCUS is a very popular message to trap. However, rather than trying to set the focus back to the control in the event that the input is incomplete, we just flag the error and allow the focus to switch normally.

CBaseEdit::OnSetFocus

WM_SETFOCUS is trapped simply so that we can set any colours we need to and display a tooltip if required.

CBaseEdit::WindowProc

This is where the rest of the Windows messages we are interested in are processed.

How to Derive Your Own Custom Control

Here are the four obvious things you might want to do:

• Override SemanticCheck

  See the CUIntRangeEdit example to see how this works.

• Trap WM_CHAR yourself

  By trapping characters yourself, you can automatically format input and perform semantic validation as the user types. Refer to theCDateTimeEdit example to see how this works.

• Trap WM_KILLFOCUS yourself

  You may want to perform extra formatting when the user leaves the control. Again, see the CDateTimeEdit example. Don't forget to callCBaseEdit::OnKillFocus if you do this!

• Override SyntaxCheck

  This is if you want to pre-process the string before running the syntax checking. See CDateTimeEdit for an example.

Example Controls Included in the ZIP

• CCurrencyEdit
• CDateTimeEdit
• CFloatEdit
• CIntEdit
• CUIntEdit
• CUIntRangeEdit
• CSpin

Tooltip Support

You might want to explain the data format for your controls at runtime. For this reason, Balloon Help support is included. To include this support, you must call CreateToolTip:

 Collapse

BOOL CEditTestDlg::OnInitDialog()
{
    CDialog::OnInitDialog ();
    ...
    m_DateEdit.CreateToolTip (this, _T("Tooltip text here"));
    ...
}

The C++ Standard Regular Expression Library

The boost::regex library has been accepted into the C++ Standard Library. Due to its partial match support, the library is also ideal for this control. Get the Boost library here.

TO DO

• Add more demo controls
• Tutorial for deriving controls

Feedback

All feedback is most welcome!