WinAPI实现按钮Hover时重绘异常问题求助

我通过WinAPI创建按钮并子类化，希望所有事件（点击、悬停等）都在按钮子类过程中处理，而非父窗口的MainWndProc。需求是鼠标悬停时改变按钮颜色，用isHover变量控制WM_PAINT的颜色选择，但发现WM_MOUSEHOVER和WM_MOUSELEAVE中已经正确修改了isHover的值，可WM_PAINT里读取的isHover却没有同步，控制台输出能确认这个问题。

原代码 #

#define UNICODE
#include <windows.h>
#include <CommCtrl.h>
#include <windowsx.h>
#include <iostream>
LRESULT CALLBACK MainWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
LRESULT CALLBACK ButtonWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    const wchar_t g_szClassName[] = L"myWindowClass";
    WNDCLASSEX wc = {0};
    HWND hwnd;
    MSG Msg;

    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = 0;
    wc.lpfnWndProc = MainWndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = CreateSolidBrush(RGB(30, 30, 30));
    wc.lpszMenuName = NULL;
    wc.lpszClassName = g_szClassName;
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

    if (!RegisterClassEx(&wc))
    {
        MessageBox(NULL, L"فشل تسجيل فئة النافذة", L"خطأ", MB_OK);
        return 1;
    }

    hwnd = CreateWindowEx(0, L"MyWindowClass", L"نافذة جديدة",
                          WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT,
                          500, 350, NULL, NULL, wc.hInstance, NULL);

    if (hwnd == NULL)
    {
        MessageBox(NULL, L"فشل إنشاء النافذة", L"خطأ", MB_OK);
        return 1;
    }
    HWND hButton1 = CreateWindowEx(0, L"BUTTON", L"button1", WS_VISIBLE | WS_CHILD | BS_FLAT,
                                   200, 200, 100, 40, hwnd, (HMENU)101, NULL, NULL);

    if (hButton1 == NULL)
    {
        MessageBox(NULL, L"فشل إنشاء الزر", L"خطأ", MB_OK);
        return 1;
    }

    SetWindowSubclass(hButton1, &ButtonWndProc, 1, 0);

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    while (Msg.message != WM_QUIT)
    {
        if (GetMessage(&Msg, NULL, 0, 0))
        {
            TranslateMessage(&Msg);
            DispatchMessage(&Msg);
        }
    }
    return 0;
}

LRESULT CALLBACK MainWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    case WM_CLOSE:
        DestroyWindow(hwnd);
        break;
    default:
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
    return 0;
}

LRESULT CALLBACK ButtonWndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData)
{
    bool isTracking;
    bool isHover;
    switch (uMsg)
    {
    case WM_NCDESTROY:
        RemoveWindowSubclass(hWnd, &ButtonWndProc, uIdSubclass);
        break;
    case WM_MOUSEMOVE:
        std::cout << "WM_MOUSEMOVE RECEIVED " << std::endl;        
        std::cout << "hovered =  " << isHover << std::endl;
        if (!isTracking)
        {
            TRACKMOUSEEVENT tme = {sizeof(TRACKMOUSEEVENT)};
            tme.dwFlags = TME_LEAVE | TME_HOVER;
            tme.hwndTrack = hWnd;
            tme.dwHoverTime = 10;
            isTracking = TrackMouseEvent(&tme);
        }
        return 0 ;
    case WM_MOUSELEAVE:
        std::cout << "(" << GET_X_LPARAM(lParam) << ", " << GET_Y_LPARAM(lParam) << ")" << std::endl;
        isTracking = FALSE;
        isHover = FALSE;
        std::cout << "WM_MOUSELEAVE RECEIVED " << std::endl; 
        std::cout << "hovered =  " << isHover << std::endl;
        InvalidateRect(hWnd, NULL, true);
        UpdateWindow(hWnd);
        return 0;
    case WM_MOUSEHOVER:
        std::cout << "(" << GET_X_LPARAM(lParam) << ", " << GET_Y_LPARAM(lParam) << ")" << std::endl;
        isTracking = TRUE;
        isHover = TRUE;
        std::cout << "WM_MOUSEHOVER RECEIVED " << std::endl;        
        std::cout << "hovered =  " << isHover << std::endl;
        InvalidateRect(hWnd, NULL, true);
        UpdateWindow(hWnd);
        return 0;
    case WM_PAINT:
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hWnd, &ps);
        HBRUSH brush;
        std::cout << "WM_PAINT RECEIVED" << std::endl;
        std::cout << "paint hovered =  " << isHover << std::endl;

        if (isHover)
        {
            brush = CreateSolidBrush(RGB(255, 0, 0));
        }
        else
        {
            brush = CreateSolidBrush(RGB(0, 255, 0));
        }

        FillRect(hdc, &ps.rcPaint, brush);
        DeleteObject(brush);
        EndPaint(hWnd, &ps);
        break;
    }
    return DefSubclassProc(hWnd, uMsg, wParam, lParam);
}

问题根源 #

你在ButtonWndProc里定义的isTracking和isHover是局部变量，每次窗口过程被调用时都会重新初始化，之前修改的值根本没被保存，导致WM_PAINT读取的始终是未初始化的垃圾值。

修复方案 #

需要把这两个状态变量改成窗口私有数据，推荐以下两种方法：

方法1：子类化传递结构体指针（多按钮安全） #

1. 定义存储状态的结构体：

typedef struct {
    bool isTracking;
    bool isHover;
} ButtonState;

2. 在WinMain中创建按钮后，分配内存并传递给子类：

ButtonState* pState = new ButtonState{false, false};
SetWindowSubclass(hButton1, &ButtonWndProc, 1, (DWORD_PTR)pState);

3. 在子类过程中通过dwRefData获取状态指针：

LRESULT CALLBACK ButtonWndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData)
{
    ButtonState* pState = reinterpret_cast<ButtonState*>(dwRefData);
    // 替换所有isTracking为pState->isTracking，isHover为pState->isHover

4. 在窗口销毁时释放内存：

case WM_NCDESTROY:
    delete reinterpret_cast<ButtonState*>(dwRefData);
    RemoveWindowSubclass(hWnd, &ButtonWndProc, uIdSubclass);
    break;

方法2：静态局部变量（仅单按钮测试用） #

如果只创建单个按钮，可以把变量改成静态局部变量，避免每次调用重新初始化：

LRESULT CALLBACK ButtonWndProc(...)
{
    static bool isTracking = false;
    static bool isHover = false;
    // 后续逻辑不变

注意：这种方法在多个按钮时会导致状态共享，严重错误，仅适合单按钮测试。

额外优化 #

• 处理WM_ERASEBKGND避免背景闪烁：

case WM_ERASEBKGND:
    return TRUE;

• 添加按钮文本绘制（当前代码仅填充背景）：
  在WM_PAINT的FillRect后添加：

wchar_t szText[256];
GetWindowText(hWnd, szText, 256);
SetTextColor(hdc, RGB(255,255,255));
SetBkMode(hdc, TRANSPARENT);
DrawText(hdc, szText, -1, &ps.rcPaint, DT_CENTER | DT_VCENTER | DT_SINGLELINE);

内容的提问来源于stack exchange，提问作者stepic Game