c++ - 使用winapi通过按钮更改窗口的背景颜色

Question

我试图让按钮在单击时更改窗口的背景颜色。我知道我需要在 WM_COMMAND 中处理此事件，我还检查了此按钮的 ID，但没有任何反应。我尝试调试，我的程序正确识别了 ID。用于更改颜色的代码片段在主循环中运行良好，但在 WM_COMMAND 中却没有任何作用。我该如何解决这个问题？完整代码:

#include <Windows.h>
#define BUTTON_ID 100

struct status_info {
    const char* waiting = "Waiting for connection...";
    const char* connected = "Connected.\nWaiting for frajer to copy number.";
    const char* changed = "Number changed.";

}status_info;

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

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow) {

const wchar_t CLASS_NAME[] = L"Name";

WNDCLASS wc = {};
wc.lpfnWndProc = WindowProc;
wc.hInstance = hInstance;
wc.lpszClassName = (LPCSTR)CLASS_NAME;
wc.hbrBackground = (HBRUSH)GetStockObject(GRAY_BRUSH);

RegisterClass(&wc);
//main window
HWND hwnd = CreateWindowEx(0, (LPCSTR)CLASS_NAME, (LPCSTR)"Hacker", WS_OVERLAPPEDWINDOW | WS_VISIBLE, CW_USEDEFAULT, CW_USEDEFAULT, 500, 300, NULL, NULL, hInstance, NULL);
//number window
HWND number = CreateWindowEx(WS_EX_WINDOWEDGE, TEXT("Static"), TEXT("Account number:\n00 1234 1234 1234 1234 1234 1234"), WS_CHILD | WS_VISIBLE, 5, 5, 240, 40, hwnd, NULL, NULL, NULL);
//status window
const char* status_message = status_info.waiting;
HWND status = CreateWindowEx(WS_EX_WINDOWEDGE, TEXT("Static"), TEXT(status_message), WS_CHILD | WS_VISIBLE, 5, 55, 240, 40, hwnd, NULL, NULL, NULL);
//button
HWND button = CreateWindowEx(0, "BUTTON", "Nightmode", WS_CHILD | WS_VISIBLE, 100, 100, 150, 30, hwnd, (HMENU)BUTTON_ID, hInstance, NULL);
MSG msg;
WNDCLASS okno;

while (GetMessage(&msg, (HWND)NULL, 0, 0)) {
    TranslateMessage(&msg);
    DispatchMessage(&msg);

    SetWindowText(status, status_message);
}
return msg.wParam;

return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_CREATE:
    //MessageBox(hwnd, L"1", L"1", 0);
    return (0);

case WM_DESTROY:
    //MessageBox(hwnd, L"2", L"2", 0);
    PostQuitMessage(0);
    return (0);

case WM_COMMAND: {
    if (LOWORD(wParam) == BUTTON_ID) {
        PAINTSTRUCT ps;
        RECT rc;
        HDC hdc = BeginPaint(hwnd, &ps);
        GetClientRect(hwnd, &rc);
        SetBkColor(hdc, BLACK_BRUSH);
        ExtTextOut(hdc, 0, 0, ETO_OPAQUE, &rc, 0, 0, 0);
        EndPaint(hwnd, &ps);
    }
    break;
}

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

Answer 1

BeginPaint/EndPaint 应仅用于响应 WM_PAINT。

您可以使用 GetDC(hwnd)/ReleaseDC(hwnd, hdc) 获取 hdc 以在 WM_PAINT 之外的设备环境上绘制，但这将是暂时的。下一条刷新消息导致窗口根据 WM_PAINT

中的内容被删除和重新绘制

SetDCBrushColor 如果目标是避免创建画笔句柄，则可以使用。

static COLORREF bkcolor = RGB(255,255,255);
switch(message)
{
case WM_COMMAND:
    if(LOWORD(wparam) == BUTTON_ID)
    {
        bkcolor = RGB(255, 0, 0);
        InvalidateRect(hwnd, NULL, TRUE);
    }
    break;

case WM_PAINT:
{
    PAINTSTRUCT ps;
    RECT rc;
    HDC hdc = BeginPaint(hwnd, &ps);
    GetClientRect(hwnd, &rc);
    SetDCBrushColor(hdc, bkcolor);
    FillRect(hdc, &rc, (HBRUSH)GetStockObject(DC_BRUSH));

    //or use ps.rcPaint to repaint only the section which requires update
    //FillRect(hdc, &ps.rcPaint, (HBRUSH)GetStockObject(DC_BRUSH));

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

case WM_ERASEBKGND:
    //return 0 means WM_PAINT handles the background
    return 0;

或者，使用 SetClassLongPtr 替换背景画笔:

static HBRUSH bkbrush = NULL;
switch(message)
{
case WM_COMMAND:
    if(LOWORD(wparam) == BUTTON_ID)
    {
        COLORREF bkcolor = RGB(rand() % 256, rand() % 256, rand() % 256);
        if(bkbrush)
            DeleteObject(bkbrush);
        bkbrush = CreateSolidBrush(bkcolor);
        SetClassLongPtr(hwnd, GCL_HBRBACKGROUND, (LONG)bkbrush);
        InvalidateRect(hwnd, NULL, TRUE);
    }
    break;