Question

问题是这样的：我有两个winapi应用程序。沟通只有一种方式。 App1向App2发送消息。 App2应该接收WM_COPYDATA，其结构具有两个形状的坐标，然后它应该绘制这些形状。收到消息。来自结构的数据是可以的。执行WM_COPYDATA案例中的代码应绘制窗口但没有任何反应（窗口只有纯白色背景）

发送消息如下所示：

HWND secondApp = FindWindowEx(NULL, NULL, _T("lab2app2"), NULL ); 
int error = GetLastError();
if(secondApp != 0) // window found, send message
{
    // prepare data
    FiguresData figuresData;
    // Set Data About Location and dimensions of figures
    // TODO
    figuresData.square_origin_x = square_origin_x;
    figuresData.square_origin_y = square_origin_y;
    figuresData.circle_origin_x = circle_origin_x;
    figuresData.circle_origin_y = circle_origin_y;

    COPYDATASTRUCT data;

    data.dwData = FIGURESDATA;
    data.cbData = sizeof( figuresData );
    data.lpData = &figuresData;
    bool value =  SendMessage(secondApp, WM_COPYDATA, (WPARAM)(HWND)mainWindow, (LPARAM)(LPVOID)&data);
}

数据数据结构很简单，只有4个整数。

App2接收消息和代码：

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
PAINTSTRUCT ps;
HDC hdc;

switch (message)
{
case WM_PAINT:

    RECT clientRectangle;
GetClientRect(hWnd, &clientRectangle);

hdc = BeginPaint(hWnd, &ps);

    // nothing really here

    EndPaint(hWnd, &ps);
    break;

case WM_COPYDATA:
    {
    PCOPYDATASTRUCT pData;
    pData = (PCOPYDATASTRUCT) lParam;

    int square_origin_x = ((FiguresData *) ( pData->lpData ))->square_origin_x;
    int square_origin_y = ((FiguresData *) ( pData->lpData ))->square_origin_y;
    int circle_origin_x = ((FiguresData *) ( pData->lpData ))->circle_origin_x;
    int circle_origin_y = ((FiguresData *) ( pData->lpData ))->circle_origin_y;
    hdc = BeginPaint(hWnd, &ps);
    HPEN oldPen = (HPEN)SelectObject(hdc, pen);
    HBRUSH oldBrush = (HBRUSH)SelectObject(hdc, backgroundBrush);
    COLORREF oldBackgroundColor = SetBkColor(hdc, backgroundColor);

    Rectangle(hdc, square_origin_x, square_origin_y, square_origin_x+ SQUARE_SIDE, square_origin_y + SQUARE_SIDE);
    Ellipse(hdc, circle_origin_x, circle_origin_y, circle_origin_x+ SQUARE_SIDE, circle_origin_y + SQUARE_SIDE);


    // Put everything back the way we found it
    SelectObject(hdc, oldPen);
    SetBkColor(hdc, oldBackgroundColor);

    EndPaint(hWnd, &ps);
    break;
    }
case WM_DESTROY:
    PostQuitMessage(0);
    break;
default:
    return DefWindowProc(hWnd, message, wParam, lParam);
    break;
}

return 0;
}

在调试器上我看到窗口句柄没问题。消息被App2发送和接收，并且WM_COPYDATA案例中的代码被执行但它没有任何效果。在App2的窗口上没有绘制任何形状，我不知道为什么。任何线索？

Answer 1

您在BeginPaint处理程序之外调用WM_PAINT。 BeginPaint返回允许仅在窗口的无效区域上绘制的设备上下文。由于您尚未调用InvalidateRect，因此窗口尚未生效，因此BeginPaint不会绘制任何内容。

作为一般规则，您应该将绘画限制在WM_PAINT处理程序中。让你的WM_COPYDATA处理程序记住需要绘制的内容，然后使窗口无效并让WM_PAINT处理程序实际绘制它。

来自SendMessage的消息应该导致绘制其他窗口，但它不会

1 个答案: