在 WM_COMMAND win32 GUI C++ 中处理 WM_LBUTTONDOWN 和 WM_LBUTTONUP

Question

我正在创建一个带有如下下拉列表的窗口：

如果我点击前四个选项中的任何一个，包括它们的子选项，那么我想处理那个选项。问题是我需要在这些选项中使用WM_LBUTTONDOWN、WM_LBUTTONUP 和其他类似的东西，但不知道如何使用。

我不知道在case WM_COMMAND 内部做什么来处理所有这些选项，所以这是我的WindowProcedure：

LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the messages */
    {
        case WM_LBUTTONDOWN
        case WM_CREATE:
            AddMenu(hwnd);
            break;

        case WM_COMMAND:

            switch(wParam)
            {
                case Line_DDA:
                    break;
                case Line_Midpoint:
                    break;
                case Line_Parametric:
                    break;

                case Ellipse_Direct:
                    break;
                case Ellipse_Polar:
                    break;
                case Ellipse_Midpoint:
                    break;

                case Line_Clipping:
                    break;

                case Convex_Filling:
                    break;

                case Load_File:
                    break;

                case Save_File:
                    break;
            }
            break;

        case WM_DESTROY:
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;
        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}

这是AddMenu()：

void AddMenu(HWND hwnd)
{
    hMenu = CreateMenu();
    HMENU hSubMenu = CreateMenu();
    HMENU hLineMenu = CreateMenu();
    HMENU hEllipseMenu = CreateMenu();

    AppendMenu(hLineMenu, MF_STRING, Line_DDA, "DDA");
    AppendMenu(hLineMenu, MF_STRING, Line_Midpoint, "Midpoint");
    AppendMenu(hLineMenu, MF_STRING, Line_Parametric, "Parametric");

    AppendMenu(hEllipseMenu, MF_STRING, Ellipse_Direct, "Direct");
    AppendMenu(hEllipseMenu, MF_STRING, Ellipse_Polar, "Polar");
    AppendMenu(hEllipseMenu, MF_STRING, Ellipse_Midpoint, "Midpoint");

    AppendMenu(hSubMenu, MF_POPUP, (UINT_PTR)hLineMenu, "Line");
    AppendMenu(hSubMenu, MF_POPUP, (UINT_PTR)hEllipseMenu, "Ellipse");
    AppendMenu(hSubMenu, MF_SEPARATOR, NULL, NULL);
    AppendMenu(hSubMenu, MF_STRING, Line_Clipping, "Line Clipping");
    AppendMenu(hSubMenu, MF_SEPARATOR, NULL, NULL);
    AppendMenu(hSubMenu, MF_STRING, Convex_Filling, "Convex Filling");
    AppendMenu(hSubMenu, MF_SEPARATOR, NULL, NULL);
    AppendMenu(hSubMenu, MF_STRING, Load_File, "Load");
    AppendMenu(hSubMenu, MF_STRING, Save_File, "Save");

    AppendMenu(hMenu, MF_POPUP,(UINT_PTR)hSubMenu , "Draw");

    SetMenu(hwnd, hMenu);
}

Answer 1

Remy Lebeau 的评论指出了正确的方向。让我们更具体一点。

在事件驱动编程中，您通常需要知道过去发生了什么，才能决定现在要做什么。当事件发生时，您需要知道事件是什么（例如，WM_LBUTTONDOWN）和当前状态。

对于您的程序，我们需要跟踪一些不同的东西，所以让我们将它们捆绑到一个结构中。

struct State {
  enum { Idle, WaitingForPoint0, WaitingForPoint1, DrawIt } action;
  DrawType type;  // e.g., Line_DDA, Line_Midpoint, Ellipse_Direct, etc.
  POINT points[2];
};

您需要某种方式将这个State 的一个实例与您的窗口的每个实例相关联。现在，我们只是将其设为全局变量，并假设您的程序中只有这种类型的窗口。

State g_state = {Idle};

当用户从菜单中选择一个绘图选项时，您会更新当前状态。例如：

case Line_DDA:
    g_state.action = WaitingForPoint0;
    g_state.type = LineDDA;
    break;

case Line_Midpoint:
    g_state.action = WaitingForPoint0;
    g_state.type = Line_Midpoint;
    break;

// and so on

当用户按下按钮时，我们必须检查当前状态以知道该做什么。

case WM_LBUTTONDOWN:
    switch (g_state.action) {
        case Idle:  // just ignore the click
            break;
        case WaitingForPoint0:
            g_state.points[0].x = GET_X_LPARAM(lParam);
            g_state.points[0].y = GET_Y_LPARAM(lParam);
            g_state.action = WaitingForPoint2;
            break;
        case WaitingForPoint1:
            g_state.points[1].x = GET_X_LPARAM(lParam);
            g_state.points[1].y = GET_Y_LPARAM(lParam);
            g_state.action = DrawIt;
            InvalidateRect(hWnd, NULL, TRUE);
            break;
    }
    return 0;

最后，当窗口需要更新时，我们检查它的状态，找出它显示的形状。

case WM_PAINT:
    PAINTSTRUCT ps;
    HDC hdc = BeginPaint(hwnd, &ps);
    if (g_state.action == DrawIt) {
      switch (g_state.type) {
          case Line_DDA:
              YourDrawLineDDA(hdc, g_state.points[0], g_state.points[1]);
              break;
          case Line_Midpoint:
              YourDrawLineMidpoint(hdc, g_state.points[0], g_state.points[1]);
              break;
          // and so on
      }
    }
    EndPaint(hwnd, &ps);
    return 0;

这可能会变得非常冗长，但它说明了您想要做的事情的基本要素。您当然可以考虑使这种类型的代码更简洁、优雅和可扩展。