I had a need for a combobox that would auto-complete, very much like the URL edit box in the toolbar of Netscape Navigator. It was actually surprisingly simple since the base
CComboBox is so rich in functionality.
The basic idea is that every time the text in the edit box changes, check to see if there is any text in the drop down list that is prefixed by this edit box text. Handle the
CBN_EDITUPDATE message to get the text change notifications, and use GetWindowText() to get the text.
CComboBox::SelectString will look for a string in the list which is prefixed by the given string, and select it into the edit box. I then select the portion of text that was added to the users typed text so that they can continue typing and have the additions ignored if they wish. That takes care of 90% of the work.
The only trick is in handling backspaces and deletes. When a user hits delete, the text is changed, and the auto-completion routine will try to restore that text back again. Just check in
PreTranslateMessage for a
KEY_DOWN message with a virtual key of
VK_BACK, and temporarily disable the auto-complete mechanism for those key strokes.
#if _MSC_VER >= 1000
class CComboCompletion : public CComboBox
virtual BOOL PreTranslateMessage(MSG* pMsg);
afx_msg void OnEditUpdate();
#include <span class="code-string">"stdafx.h"</span>