Unable to add thumbnail buttons to a window?

Question

I'm trying to add thumbnail buttons to a window, but there is no error and no thumbnail button is shown. I read the following pages for reference:

1. Your First Windows Program ;

2. ITaskbarList3::ThumbBarAddButtons method ;

3. some code on github .

Environment: win10 64bit, vs2015

// function WindowProc and wWinMain are copied from msdn directly.

#include "stdafx.h"
#include <windows.h>
#include "shobjidl.h" 
#include <exception>


LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

HRESULT addThumbnailButtons(HWND hwnd) {
    HRESULT hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE);
    if (SUCCEEDED(hr)) {
        ITaskbarList4* ptbl = nullptr;
        HRESULT hr = CoCreateInstance(CLSID_TaskbarList, NULL, CLSCTX_INPROC_SERVER,
            IID_PPV_ARGS(&ptbl));

        if (SUCCEEDED(hr)) {
            // create 2 buttons
            THUMBBUTTON thmb[2] = {};

            thmb[0].dwMask = THB_TOOLTIP;
            thmb[0].iId = 0;
            wcscpy_s(thmb[0].szTip, L"Button 1");

            thmb[1].dwMask = THB_TOOLTIP;
            thmb[1].iId = 1;
            wcscpy_s(thmb[1].szTip, L"Button 2");

            //ptbl->HrInit();
            hr = ptbl->ThumbBarAddButtons(hwnd, ARRAYSIZE(thmb), thmb);

            ptbl->Release();

            return hr;
        }
        else {
            throw std::exception("createInstance failed");
        }
    }else{
        throw std::exception("coinitialize failed");
    }
}

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
    // Register the window class.
    const wchar_t CLASS_NAME[] = L"Sample Window Class";

    WNDCLASS wc = {};

    wc.lpfnWndProc = WindowProc;
    wc.hInstance = hInstance;
    wc.lpszClassName = CLASS_NAME;

    RegisterClass(&wc);

    // Create the window.

    HWND hwnd = CreateWindowEx(
        0,                              // Optional window styles.
        CLASS_NAME,                     // Window class
        L"Learn to Program Windows",    // Window text
        WS_OVERLAPPEDWINDOW,            // Window style

                                        // Size and position
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

        NULL,       // Parent window    
        NULL,       // Menu
        hInstance,  // Instance handle
        NULL        // Additional application data
    );

    if (hwnd == NULL)
    {
        return 0;
    }

    HRESULT hr = addThumbnailButtons(hwnd);
    if (FAILED(hr)) {
        throw std::exception("addbuttons failed");
    }

    ShowWindow(hwnd, nCmdShow);

    // Run the message loop.

    MSG msg = {};
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;

    case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);

        FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));

        EndPaint(hwnd, &ps);
    }
    return 0;

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

Answer 1

Per the ITaskBarList3 documentation:

When an application displays a window, its taskbar button is created by the system. When the button is in place, the taskbar sends a TaskbarButtonCreated message to the window. Your application should call RegisterWindowMessage(L"TaskbarButtonCreated") and handle that message in its wndproc. That message must be received by your application before it calls any ITaskbarList3 method .

You must wait for that message before calling addThumbnailButtons() , eg:

UINT uMsgTaskbarCreated;

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
    uMsgTaskbarCreated = RegisterWindowMessage(L"TaskbarButtonCreated");

    // Register the window class.
    const wchar_t CLASS_NAME[] = L"Sample Window Class";

    WNDCLASS wc = {};

    wc.lpfnWndProc = WindowProc;
    wc.hInstance = hInstance;
    wc.lpszClassName = CLASS_NAME;

    RegisterClass(&wc);

    // Create the window.

    HWND hwnd = CreateWindowEx(
        0,                              // Optional window styles.
        CLASS_NAME,                     // Window class
        L"Learn to Program Windows",    // Window text
        WS_OVERLAPPEDWINDOW,            // Window style

                                        // Size and position
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

        NULL,       // Parent window    
        NULL,       // Menu
        hInstance,  // Instance handle
        NULL        // Additional application data
    );

    if (hwnd == NULL)
    {
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);

    // Run the message loop.

    MSG msg = {};
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;

        case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);

            FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));

            EndPaint(hwnd, &ps);
            return 0;
        }

        default:
            if ((uMsg == uMsgTaskbarCreated) && (uMsgTaskbarCreated != 0))
            {
                HRESULT hr = addThumbnailButtons(hwnd);
                if (FAILED(hr)) {
                    ...;
                }
            }
            break;
        }

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