使用winapi使用按钮更改窗口的背景颜色

Question

我正在尝试使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 ID。用于更改颜色的代码段在主循环中运行良好，但在WM_COMMAND中则不执行任何操作。如何解决此问题？整个代码：

#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应该仅用于响应WM_PAINT。

您可以使用GetDC(hwnd)/ReleaseDC(hwnd, hdc)获取在WM_PAINT之外的设备上下文上绘制的hdc，但这将是暂时的。下一条刷新消息会导致窗口根据WM_PAINT中的内容被擦除和重新绘制

如果目标是避免创建画笔手柄，则可以使用SetDCBrushColor。

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;