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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_DELETE or VK_BACK, and temporarily
disable the auto-complete mechanism for those key strokes.
Source code
#if !defined(AFX_COMBOBOXEX_H__115F422E_5CD5_11D1_ABBA_00A0243D1382__INCLUDED_) #define AFX_COMBOBOXEX_H__115F422E_5CD5_11D1_ABBA_00A0243D1382__INCLUDED_ #if _MSC_VER >= 1000 #pragma once #endif // _MSC_VER >= 1000 // ComboBoxEx.h : header file // // Copyright (c) Chris Maunder 1997. // Please feel free to use and distribute. ///////////////////////////////////////////////////////////////////////////// // CComboBoxEx window class CComboBoxEx : public CComboBox { // Construction public: CComboBoxEx(); // Attributes public: // Operations public: // Overrides // ClassWizard generated virtual function overrides //{{AFX_VIRTUAL(CComboBoxEx) public: virtual BOOL PreTranslateMessage(MSG* pMsg); //}}AFX_VIRTUAL // Implementation public: virtual ~CComboBoxEx(); BOOL m_bAutoComplete; // Generated message map functions protected: //{{AFX_MSG(CComboBoxEx) afx_msg void OnEditUpdate(); //}}AFX_MSG DECLARE_MESSAGE_MAP() }; ///////////////////////////////////////////////////////////////////////////// //{{AFX_INSERT_LOCATION}} // Microsoft Developer Studio will insert additional declarations immediately before the previous line. #endif // !defined(AFX_COMBOBOXEX_H__115F422E_5CD5_11D1_ABBA_00A0243D1382__INCLUDED_) // ComboBoxEx.cpp : implementation file // // Copyright (c) Chris Maunder 1997. // Please feel free to use and distribute. #include "stdafx.h" #include "ComboBoxEx.h" #ifdef _DEBUG #define new DEBUG_NEW #undef THIS_FILE static char THIS_FILE[] = __FILE__; #endif ///////////////////////////////////////////////////////////////////////////// // CComboBoxEx CComboBoxEx::CComboBoxEx() { m_bAutoComplete = TRUE; } CComboBoxEx::~CComboBoxEx() { } BEGIN_MESSAGE_MAP(CComboBoxEx, CComboBox) //{{AFX_MSG_MAP(CComboBoxEx) ON_CONTROL_REFLECT(CBN_EDITUPDATE, OnEditUpdate) //}}AFX_MSG_MAP END_MESSAGE_MAP() ///////////////////////////////////////////////////////////////////////////// // CComboBoxEx message handlers BOOL CComboBoxEx::PreTranslateMessage(MSG* pMsg) { // Need to check for backspace/delete. These will modify the text in // the edit box, causing the auto complete to just add back the text // the user has just tried to delete. if (pMsg->message == WM_KEYDOWN) { m_bAutoComplete = TRUE; int nVirtKey = (int) pMsg->wParam; if (nVirtKey == VK_DELETE || nVirtKey == VK_BACK) m_bAutoComplete = FALSE; } return CComboBox::PreTranslateMessage(pMsg); } // if we are not to auto update the text, get outta here if (!m_bAutoComplete) return; // Get the text in the edit box CString str; GetWindowText(str); int nLength = str.GetLength(); // Currently selected range DWORD dwCurSel = GetEditSel(); WORD dStart = LOWORD(dwCurSel); WORD dEnd = HIWORD(dwCurSel); // Search for, and select in, and string in the combo box that is prefixed // by the text in the edit box if (SelectString(-1, str) == CB_ERR) { SetWindowText(str); // No text selected, so restore what was there before if (dwCurSel != CB_ERR) SetEditSel(dStart, dEnd); //restore cursor postion } // Set the text selection as the additional text that we have added if (dEnd < nLength && dwCurSel != CB_ERR) SetEditSel(dStart, dEnd); else SetEditSel(nLength, -1);
Last updated: 12 Sep 1998