ComboBoxEx32 (CComboBoxEx) keyboard behaviour

Question

I have a WTL application that uses an extended combobox control (the Win32 class ComboBoxEx32) with the CBS_DROPDOWNLIST style. It works well (I can have images against each item in the box) but the keyboard behaviour is different to a normal combobox - pressing a key will not jump to the first item in the combo that starts with that letter.

For example, if I add the strings 'Arnold', 'Bob' and 'Charlie' to the combo, if I then select the combo and press 'B', then 'Bob' won't be selected.

Does anyone know how to make this work? Currently the only idea I can think of is to somehow subclass the 'actual' combobox (I can get the handle to this using the CBEM_GETCOMBOCONTROL message) and process WM_CHARTOITEM. This is a PITA so I thought I'd ask if anyone else has come across this issue before.

Answer 1

In the end I hooked the combobox control (obtained with CBEM_GETCOMBOCONTROL) and trapped the WM_CHARTOITEM message and performed my own lookup. I can post code if anyone else is interested.

Answer 2

I created a working solution and want to share that:

ComboBoxExKeyboardSupport.h

#pragma once

class CComboBoxExKeyboardSupport
{
// Construction
public:
    CComboBoxExKeyboardSupport( void );
    ~CComboBoxExKeyboardSupport( void );

// Attributes
private:
    static CSimpleMap<HWND, CComboBoxExKeyboardSupport*> responsibleMap;

    HWND hComboBoxHwnd;
    WNDPROC fpOriginalWndProc;

// Operations
private:
    static LRESULT CALLBACK StaticWndProc( HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam );
    LRESULT WndProc( HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam );
    LRESULT HandleCharToItemMessage( HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam );

    bool IsWindowsXPPlatform( void );
    bool InputMatches( CString inputChar, CString& itemText );

public:
    void Attach( CComboBoxEx& comboBoxEx );
    void Detach( void );
};

ComboBoxExKeyboardSupport.cpp

#include "StdAfx.h"
#include "ComboBoxExKeyboardSupport.h"

// Static member
CSimpleMap<HWND, CComboBoxExKeyboardSupport*> CComboBoxExKeyboardSupport::responsibleMap;

CComboBoxExKeyboardSupport::CComboBoxExKeyboardSupport( void )
{
    hComboBoxHwnd = nullptr;
    fpOriginalWndProc = nullptr;
}

CComboBoxExKeyboardSupport::~CComboBoxExKeyboardSupport( void )
{
    Detach( );
}

void CComboBoxExKeyboardSupport::Attach( CComboBoxEx& comboBoxEx )
{
    ATLASSERT( hComboBoxHwnd == nullptr );
    if( hComboBoxHwnd != nullptr )
        return;

    if( !IsWindowsXPPlatform( ) )
        return;

    LONG_PTR lpNewWndProc = reinterpret_cast<LONG_PTR>( StaticWndProc );
    LONG_PTR lpOldWndProc = 0;

    //----
    hComboBoxHwnd = comboBoxEx.GetComboBoxCtrl( )->GetSafeHwnd( );
    ATLASSERT( hComboBoxHwnd != nullptr );

    // Exchange the WndProc
    lpOldWndProc = SetWindowLongPtr( hComboBoxHwnd, GWLP_WNDPROC, lpNewWndProc );
    ATLASSERT( lpOldWndProc != 0 );
    fpOriginalWndProc = reinterpret_cast<WNDPROC>( lpOldWndProc ); 

    // Remember the handle and the old WndProc
    responsibleMap.Add( hComboBoxHwnd, this );
}

void CComboBoxExKeyboardSupport::Detach( void )
{
    if( hComboBoxHwnd == nullptr )
        return;

    //----
    LONG_PTR lpResult = 0;

    // Reset original WndProc
    lpResult = SetWindowLongPtr( hComboBoxHwnd, GWLP_WNDPROC,
        reinterpret_cast<LONG_PTR>( fpOriginalWndProc ) );
    ATLASSERT( lpResult != 0 );

    // Remove handle and WndProc from map
    responsibleMap.Remove( hComboBoxHwnd );

    //----
    hComboBoxHwnd = nullptr;
    fpOriginalWndProc = nullptr;
}

bool CComboBoxExKeyboardSupport::IsWindowsXPPlatform( void )
{
    OSVERSIONINFO osvi = {0};
    bool bResult = false;

    //----
    osvi.dwOSVersionInfoSize = sizeof( OSVERSIONINFO );
    if( GetVersionEx( &osvi ) )
    {
        // 5.1 = Windows XP
        // 5.2 = Windows Server 2003, Windows Server 2003 R2
        bResult = ( osvi.dwMajorVersion == 5 &&
            ( osvi.dwMinorVersion == 1 || osvi.dwMinorVersion == 2 ) );
    }

    return bResult;
}

LRESULT CComboBoxExKeyboardSupport::StaticWndProc( HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam )
{
    CComboBoxExKeyboardSupport* pResponsibleClass = nullptr;

    // Get responsible class from map
    pResponsibleClass = responsibleMap.Lookup( hwnd );
    ATLASSERT( pResponsibleClass != nullptr );

    //----
    return pResponsibleClass->WndProc( hwnd, uMsg, wParam, lParam );
}

LRESULT CComboBoxExKeyboardSupport::WndProc( HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam )
{
    // Save originalWndProc because after WM_DESTROY/Detach the member variable is nullptr.
    WNDPROC fpOriginalWndProc = this->fpOriginalWndProc;

    //----
    if( uMsg == WM_DESTROY )
    {
        Detach( );
    }
    else if( uMsg == WM_CHARTOITEM )
    {
        return HandleCharToItemMessage( hwnd, uMsg, wParam, lParam );
    }

    //----
    return ::CallWindowProc( fpOriginalWndProc, hwnd, uMsg, wParam, lParam );
}

LRESULT CComboBoxExKeyboardSupport::HandleCharToItemMessage(
    HWND hwnd,
    UINT uMsg,
    WPARAM wParam,
    LPARAM lParam )
{
    //----
    LRESULT lResult = CB_ERR;
    CComboBox* pComboBox = nullptr;
    int itemCount = 0;
    int itemSelected = 0;
    CString itemText;
    TCHAR inputCharacter = 0;

    //----
    pComboBox = (CComboBox*)CComboBox::FromHandle( hwnd );

    //----
    itemCount = pComboBox->GetCount( );
    itemSelected = pComboBox->GetCurSel( );
    inputCharacter = static_cast<TCHAR>( LOWORD( wParam ) );

    // Search from the current selected item plus one to the end
    for( int i = (itemSelected + 1); i < itemCount; i++ )
    {
        pComboBox->GetLBText( i, itemText );
        if( InputMatches( inputCharacter, itemText ) )
        {
            lResult = i;
            break;
        }
    }

    if( lResult == CB_ERR )
    {
        // Search from the beginning to the selected item minus one.
        for( int i = 0; i < itemSelected; i++ )
        {
            pComboBox->GetLBText( i, itemText );
            if( InputMatches( inputCharacter, itemText ) )
            {
                lResult = i;
                break;
            }
        }
    }

    //----
    return lResult;
}

bool CComboBoxExKeyboardSupport::InputMatches( CString inputChar, CString& itemText )
{
    CString firstCharString;
    bool bInputMatches = false;

    //----
    firstCharString = itemText;
    firstCharString.Left( 1 );

    //----
    bInputMatches = firstCharString.CompareNoCase( inputChar ) == 0;

    //----
    return bInputMatches;
}

Answer 3

My suggestion is to ditch CComboBoxEx and draw the icon with an owner-draw regular combo box. CComboBoxEx is slightly different from the 'normal' combobox but in just enough ways that I suspect it's a complete re-implementation. Notice how a selected item looks slightly different from one that is selected in a normal combo box, as well.

Owner draw controls in WTL are quite easy to implement with the COwnerDraw mixin.

Not an answer to your question, just letting you know that that's how I deal CComboBoxEx nowadays :)

Answer 4

In our application, the keyboard behaviour you described was lost between versions. As it turns out, we removed an additional manifest dependency, which resulted in a dependency on an older version of comctl32.dll (5.82). This line in the project settings, Configuration Properties -> Linker -> Manifest File -> Additional Manifest Dependencies:

type='win32' name='Microsoft.Windows.Common-Controls' version='6.0.0.0' processorArchitecture='' publicKeyToken='6595b64144ccf1df' language=''

fixed it for us.

Using Dependency Walker, one can check that the app is now only dependent on comctl32.dll version 6.10, which has the correct behaviour.