Question

I am having trouble using the function SHAutoComplete. It simply does not work correctly when I use it on a edit box whose parent window is not a dialog box.

The auto-complete functionality seems to be working fine, but the rendering of the drop-down list with the possible candidates based on what was typed on the edit box is very messed up. Basically only the borders of the drop-down are shown. The borders are rendered wide enough to fit the possible suggestions, but the suggestions themselves are never drawn. Even the drop-down list background color is wrong. It is as if it was never painted and remains with the original parent window color.

And if the number of suggestions is big enough so the drop-down needs a scroll-bar, the scrollbar also does not get rendered correctly – the arrows do not get drawn.

On both cases, with or without scrollbars, the drop-down list does not accept mouse input, i.e., I cannot click on the items. If I press the “down” key on the keyboard while the drop-down is being shown, it kind of works as expected. After the second or third press the items finally start to appear. But the scrollbar still is does not get rendered correctly.

If instead of registering my own windows class I simply use a dialog with ::DialogBoxParam(), then it all goes as expected. The auto-complete works without any problems at all.

Here is what I am doing. This code will register a window class, create the main window, create an edit box and then call SHAutoComplete on it. It must be linked with Shlwapi.lib

// this code must be linked with Shlwapi.lib

#include <Windows.h>
#include <Shlwapi.h>


// name of the class that will be created for the main window
static const char WindowClassName[] = "SHAutoCompleteDoesNotWorkWithoutADialogWindowClassName";


// the main window procedure
static LRESULT CALLBACK WindowProc(
    HWND   hwnd,
    UINT   uMsg,
    WPARAM wParam,
    LPARAM lParam)
{
    switch(uMsg)
    {   
        case WM_CREATE:
        {
            HWND hwndEdit = ::CreateWindowEx(
                0,
                "EDIT",
                0,
                WS_CHILD | WS_VISIBLE,
                10, 
                10, 
                300,
                25,
                hwnd, 
                NULL,
                NULL,
                0);     

            ::SHAutoComplete(hwndEdit, SHACF_DEFAULT);

            return 0;
        }            

        case WM_DESTROY:
            ::PostQuitMessage(1);
            return 0;

        default:
            return ::DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
}


// the app entry point
int CALLBACK WinMain(
    HINSTANCE hInstance,
    HINSTANCE hPrevInstance,
    LPSTR    lpCmdLine,
    int       nCmdShow)
{
    ::CoInitialize(NULL);

    WNDCLASSEX wcex    = {0};
    wcex.cbSize        = sizeof(wcex);
    wcex.style         = CS_OWNDC | CS_HREDRAW | CS_VREDRAW ;
    wcex.lpfnWndProc   = WindowProc;
    wcex.hInstance     = hInstance;        
    wcex.lpszClassName = WindowClassName;
    wcex.hbrBackground = (HBRUSH)(COLOR_BTNFACE+1); 

    ATOM atom = ::RegisterClassEx(&wcex);

    HWND hwnd = ::CreateWindowEx(
        0,
        MAKEINTATOM(atom),
        "SHAutoComplete Test",
        WS_OVERLAPPEDWINDOW | WS_VISIBLE |  WS_CLIPCHILDREN | WS_CLIPSIBLINGS,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        NULL,
        NULL,
        hInstance,
        NULL);

    MSG msg;
    while(::GetMessage(&msg, hwnd, 0, 0) > 0)
    {
        ::TranslateMessage(&msg);
        ::DispatchMessage(&msg);
    }

    ::UnregisterClass((LPCTSTR)atom, NULL);

    ::CoUninitialize();

    return 0;
}       

That code produces the following:

1. the drop-down when a scroll bar is needed
   http://www.abload.de/img/shautocomplete_2i1sk4.jpg

2. the drop-down after a couple of presses to the “down” key. Notice how the scroll bar still is not rendered correctly.
   http://www.abload.de/img/shautocomplete_3efsgw.jpg

Now, when I switch to Dialog Boxes, works like a charm. In the code below, IDD_DIALOG1 is simply an empty dialog box resource, created automatically by the IDE.

Here is the relevant part of the rc file

IDD_DIALOG1 DIALOGEX 0, 0, 316, 185
STYLE DS_SETFONT | DS_MODALFRAME | DS_FIXEDSYS | WS_POPUP | WS_CAPTION | WS_SYSMENU
CAPTION "Dialog"
FONT 8, "MS Shell Dlg", 400, 0, 0x1
BEGIN
END

And here is the code that uses it

// this code must be linked with Shlwapi.lib

#include <windows.h>
#include <Shlwapi.h>

#include "Resource.h"


BOOL CALLBACK DialogProc(
    HWND   hwnd,
    UINT   uMsg,
    WPARAM wParam,
    LPARAM lParam)
{    

    switch(uMsg)
    {        
        case WM_INITDIALOG:
        {
            HWND hwndEdit = ::CreateWindowEx(
                0,
                "EDIT",
                0,
                WS_VISIBLE | WS_CHILD,                    
                0, 
                0, 
                300,
                20,
                hwnd, 
                NULL,
                NULL,
                0);      

            ::SHAutoComplete(hwndEdit, SHACF_DEFAULT);

            return 1;
        }


        case WM_CLOSE:            
            ::EndDialog(hwnd, 0);
            return 1;   


        default:
            return 0;
    }
}



int WINAPI WinMain(
    HINSTANCE hInstance,
    HINSTANCE hPrevInstance,
    LPSTR     lpCmdLine,
    int       nShowCmd)
{       
    ::CoInitialize(NULL);

    ::DialogBoxParam(
        NULL,
        MAKEINTRESOURCE(IDD_DIALOG1),
        NULL,
        DialogProc,
        0);    

    ::CoUninitialize();

    return 0;
}

Could you please point out where I am going wrong? As far as I can see, other than the creation and destruction of the main window, there seems to be no difference at all between the two of them. Am I missing something on the SHAutoComplete docs that states it can only be used on edit boxes inside dialogs?

Answer 1

You are using a filtered message loop so any messages for the drop down are not being processed. Pass NULL as the second parameter to GetMessage