WIN32 多窗口

Question

我試圖顯示 3 個窗口，但是它無法創建窗口 2，我不知道為什么。 它創建了第一個窗口，我對其他兩個窗口也做了同樣的事情。

這是代碼：

#include <Windows.h>

// Store handles to the main window and application instance globally.
HWND      ghMainWnd = 0;
HWND      ghSecdWnd = 0;
HWND      ghThrdWnd = 0;
HINSTANCE ghAppInst = 0;

//========================================================================================
// WINDOW 1
// Step 1: Define and implement the window procedure.
LRESULT CALLBACK
WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{

    switch( msg )
    {
    // Handle left mouse button click message.
    case WM_LBUTTONDOWN:
        MessageBox(hWnd, "Left Mouse Button Click", "Message", MB_OK);
        return 0;

    // Handle key down message.
    case WM_KEYDOWN:
        if( wParam == VK_ESCAPE )
            if( MessageBox(hWnd, "Are you sure?", "Quit", MB_YESNO) == IDYES )
                DestroyWindow(ghMainWnd);
        return 0;

    // Handle destroy window message.
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }

    // Forward any other messages we didn't handle to the default window procedure.
    return DefWindowProc(hWnd, msg, wParam, lParam);

}
//========================================================================================
// WINDOW 2
//========================================================================================
LRESULT CALLBACK
WndProc2(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{

    switch( msg )
    {
    // Handle down arrow pressed.
    case WM_KEYDOWN:
        if( wParam == VK_DOWN )
            MessageBox(hWnd, "Down arrow pressed 2.", "Information", MB_OK);
        return 0;
    case WM_LBUTTONDOWN:
        MessageBox(hWnd, "Window 2", "Window 2", MB_OK);
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }

    return DefWindowProc(hWnd, msg, wParam, lParam);
}
//========================================================================================
// WINDOW 3
//========================================================================================
LRESULT CALLBACK
WndProc3(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{

    switch( msg )
    {
    // Handle down arrow pressed.
    case WM_KEYDOWN:
        if( wParam == VK_DOWN )
            MessageBox(hWnd, "Down arrow pressed 3.", "Information", MB_OK);
        return 0;
    case WM_LBUTTONDOWN:
        MessageBox(hWnd, "Window 3", "Window 3", MB_OK);
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }

    return DefWindowProc(hWnd, msg, wParam, lParam);
}

// WinMain: Entry point for windows application.
int WINAPI
    WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR cmdLine, int showCmd)
{

    // Save handle to application instance.
    ghAppInst = hInstance;

    // Step 2: Fill out a WNDCLASS instance.
    WNDCLASS wc;
    wc.style         = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = ghAppInst;
    wc.hIcon         = ::LoadIcon(0, IDI_APPLICATION);
    wc.hCursor       = ::LoadCursor(0, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);
    wc.lpszMenuName  = 0;
    wc.lpszClassName = "MyWndClassName";

    // Window 2
    WNDCLASS wc2;
    wc2.style         = CS_HREDRAW | CS_VREDRAW;
    wc2.lpfnWndProc   = WndProc2;
    wc2.cbClsExtra    = 0;
    wc2.cbWndExtra    = 0;
    wc2.hInstance     = ghAppInst;
    wc.hIcon          = ::LoadIcon(0, IDI_APPLICATION);
    wc2.hCursor       = ::LoadCursor(0, IDC_ARROW);
    wc2.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);
    wc2.lpszMenuName  = 0;
    wc2.lpszClassName = "MyWndClassTwo";

    // Window 3
    WNDCLASS wc3;
    wc3.style         = CS_HREDRAW | CS_VREDRAW;
    wc3.lpfnWndProc   = WndProc3;
    wc3.cbClsExtra    = 0;
    wc3.cbWndExtra    = 0;
    wc3.hInstance     = ghAppInst;
    wc3.hIcon         = ::LoadIcon(0, IDI_APPLICATION);
    wc3.hCursor       = ::LoadCursor(0, IDC_ARROW);
    wc3.lpszMenuName  = 0;
    wc3.lpszClassName = "MyWndClassThree";


    // Step 3: Register with WNDCLASS instance with windows.
    RegisterClass( &wc );
    RegisterClass( &wc2 );
    RegisterClass( &wc3 );

    // Step 4: Create the window, and save the handle in global window handle variable ghMainWnd.
    ghMainWnd = ::CreateWindow("MyWndClassName",  "Window 1", WS_OVERLAPPEDWINDOW | WS_HSCROLL | WS_VSCROLL, 0,   0,   500, 500, 0, 0, ghAppInst, 0);
    ghSecdWnd = ::CreateWindow("MyWndClassTwo",   "Window 2", WS_OVERLAPPEDWINDOW | WS_HSCROLL | WS_VSCROLL, 510, 0,   500, 500, 0, 0, ghAppInst, 0);
    ghThrdWnd = ::CreateWindow("MyWndClassThree", "Window 3", WS_OVERLAPPEDWINDOW | WS_HSCROLL | WS_VSCROLL, 0,   510, 500, 500, 0, 0, ghAppInst, 0);

    if( ghMainWnd == 0 )
    {
        ::MessageBox(0, "Create Window 1 - Failed", 0, 0);
        return false;
    }

    if( ghSecdWnd == 0 )
    {
        ::MessageBox(0, "Create Window 2 - Failed", 0, 0);
        return false;
    }

    if( ghThrdWnd == 0 )
    {
        ::MessageBox(0, "Create Window 3 - Failed", 0, 0);
        return false;
    }

    // Step 5: Show and update the window.
    ShowWindow(ghMainWnd, showCmd);
    UpdateWindow(ghMainWnd);

    ShowWindow(ghSecdWnd, showCmd);
    UpdateWindow(ghSecdWnd);

    ShowWindow(ghThrdWnd, showCmd);
    UpdateWindow(ghThrdWnd);

    // Step 6: Enter the message loop and don't quit until a WM_QUIT message is received.
    MSG msg;
    ZeroMemory(&msg, sizeof(MSG));

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

    // Return exit code back to operating system.
    return (int)msg.wParam;

}

它不會拋出任何錯誤，但在 ghSecdWnd == 0 上它會顯示該錯誤消息。

Answer 1

有兩個問題：一個是您遇到的問題，另一個是窗口 3。

在創建第二個窗口之后（但在創建第三個窗口之前GetLastError()調用GetLastError()導致"Cannot find the window class." . 查看類設置，您已完成以下操作：

wc.hIcon = ::LoadIcon(0, IDI_APPLICATION);

你真正需要的是設置wc2的圖標。 甚至在注冊第二個類的時候檢查RegisterClass的返回值都會報錯"The parameter is incorrect." ，表示wc2有問題。 它也是代碼中更早的位置來捕獲錯誤，這總是一件好事。

---

其次，第三個窗口有問題。 您尚未在其上設置背景畫筆。 將此行添加到wc3設置：

wc3.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);

---

您應該始終查看文檔以了解函數在失敗時會做什么並采取適當的措施。 例如，如果CreateWindow失敗，則返回值為NULL ，您可以調用GetLastError以獲取更多信息。 您應該在每個功能的基礎上執行此操作。 這是 Window 2 的兩個主要函數的示例。請記住，其他函數（例如GetStockObject ）也可能失敗。

if (!RegisterClass(&wc2)) { //returns 0 if failed
    std::cout << "Failed to register class: ";
    std::cout << GetLastError() << '\n'; //or however you want to show it
}

if (!(ghSecdWnd = CreateWindow( /*...*/)) { //or ghSecdWnd = ...; if (!ghSecdWnd)
    std::cout << "Failed to create window: ";
    std::cout << GetLastError() << '\n'; //look at FormatMessage for a message
}

首先，查看RegisterClass ，您會在Return value下看到它在失敗時返回 0 並聲明您可以調用GetLastError()以獲取擴展錯誤信息，因此我將其輸出。 CreateWindow表示相同，但​​它是NULL因為HWND是一個指針。 您可以獲取獲得的錯誤代碼並對照 MSDN 系統錯誤代碼文章進行檢查，或者使用FormatMessage和FORMAT_MESSAGE_FROM_SYSTEM來為您執行此操作。