如何修复“'hwndButton'的初始化被'case'标签跳过”和hwndButton'被'default'标签跳过”

Posted 2023-02-22

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【中文标题】如何修复“\'hwndButton\'的初始化被\'case\'标签跳过”和hwndButton\'被\'default\'标签跳过”【英文标题】：How to fix "initialization of 'hwndButton' is skipped by 'case' label" and hwndButton' is skipped by 'default' label"如何修复“'hwndButton'的初始化被'case'标签跳过”和hwndButton'被'default'标签跳过” 【发布时间】：2019-09-09 21:58:19 【问题描述】：

我对编程比较陌生，我想尝试看看如何在 Visual Studio 2019 中制作基本的 Windows 桌面应用程序。由于我为按钮添加了代码，因此 C2360 和 C2361 错误不断弹出，我没有知道代码中的原因是什么。

我查找了一些解决方案，例如将放在代码块周围，但这些似乎不起作用。

// HelloWindowsDesktop.cpp
// compile with: /D_UNICODE /DUNICODE /DWIN32 /D_WINDOWS /c

#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <tchar.h>

// Global variables

// The main window class name.
static TCHAR szWindowClass[] = _T("DesktopApp");

// The string that appears in the application's title bar.
static TCHAR szTitle[] = _T("WIndows Application test");

HINSTANCE hInst;

// Forward declarations of functions included in this code module:
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM );

int CALLBACK WinMain(
    _In_ HINSTANCE hInstance,
    _In_ HINSTANCE hPrevInstance,
    _In_ LPSTR     lpCmdLine,
    _In_ int       nCmdShow
)

    WNDCLASSEX wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc = WndProc;
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = hInstance;
    wcex.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName = szWindowClass;
    wcex.hIconSm = LoadIcon(wcex.hInstance, IDI_APPLICATION);

    if (!RegisterClassEx(&wcex))
    
        MessageBox(NULL,
            _T("Call to RegisterClassEx failed!"),
            _T("Windows Desktop Guided Tour"),
            NULL);

        return 1;
    

    // Store instance handle in our global variable
    hInst = hInstance;

    // The parameters to CreateWindow explained:
    // szWindowClass: the name of the application
    // szTitle: the text that appears in the title bar
    // WS_OVERLAPPEDWINDOW: the type of window to create
    // CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
    // 500, 100: initial size (width, length)
    // NULL: the parent of this window
    // NULL: this application does not have a menu bar
    // hInstance: the first parameter from WinMain
    // NULL: not used in this application
    HWND hWnd = CreateWindow(
        szWindowClass,
        szTitle,
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT,
        500, 100,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    if (!hWnd)
    
        MessageBox(NULL,
            _T("Call to CreateWindow failed!"),
            _T("Windows Desktop Guided Tour"),
            NULL);

        return 1;
    

    // The parameters to ShowWindow explained:
    // hWnd: the value returned from CreateWindow
    // nCmdShow: the fourth parameter from WinMain
    ShowWindow(hWnd,
        nCmdShow);
    UpdateWindow(hWnd);

    // Main message loop:
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    

    return (int)msg.wParam;


//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)

    PAINTSTRUCT ps;
    HDC hdc;
    TCHAR greeting[] = _T("Hey Guys, this is my first Visual Studio desktop application, it has 158 lines of code!!!!!");

    switch (message)
    
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);

        // Here your application is laid out.
        // For this introduction, we just print out "Hello, Windows desktop!"
        // in the top left corner.
        TextOut(hdc,
            5, 5,
            greeting, _tcslen(greeting));

        HWND hwndButton = CreateWindow(
            L"BUTTON",  // Predefined class; Unicode assumed 
            L"OK",      // Button text 
            WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON,  // Styles 
            10,         // x position 
            10,         // y position 
            100,        // Button width
            100,        // Button height
            hWnd,     // Parent window
            NULL,       // No menu.
            (HINSTANCE)GetWindowLong(hWnd, GWL_HINSTANCE),
            NULL);      // Pointer not needed.

        // End application-specific layout section.

        EndPaint(hWnd, &ps);
        break;

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

    return 0;

预期的输出是一个新窗口，其中包含一些文本和一个按钮，将出现在左上角，但只显示文本。出现以下错误：

错误 C2360，'hwndButton' 的初始化被 'case' 标签跳过，第 149 行

错误 C2361，“默认”标签跳过了“hwndButton”的初始化，第 152 行

【问题讨论】：

HWND hwndButton = CreateWindow( 您不能在案例中创建新变量。您可以引入一个范围来消除错误。 Why can't variables be declared in a switch statement?的可能重复在 case 语句代码周围放置大括号。您不会在代码中的其他任何地方使用 hwndButton，因此编译器现在会很高兴。然而，你明天是否会快乐不太可能，每次绘画时都创建一个按钮是很不寻常的。这通常在 WM_CREATE 的消息处理程序中完成，因此只执行一次。而且您通常需要一个全局变量，以便以后可以引用该按钮。不要创建按钮来响应WM_PAINT。为WM_CREATE: 添加一个新案例，并将HWND hwndButton = CreateWindow 移入其中。 【参考方案1】：

添加HWND hwndButton的声明，将CreateWindow移到WM_CREATE。另外，将TCHAR greeting[]移出WndProc()

#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <tchar.h>

// Global variables

// The main window class name.
static TCHAR szWindowClass[] = _T("DesktopApp");

// The string that appears in the application's title bar.
static TCHAR szTitle[] = _T("WIndows Application test");

TCHAR greeting[] = _T("Hey Guys, this is my first Visual Studio desktop application, it has 158 lines of code!!!!!");

HINSTANCE hInst;
HWND hwndButton; // add here

// Forward declarations of functions included in this code module:
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int CALLBACK WinMain(
    _In_ HINSTANCE hInstance,
    _In_ HINSTANCE hPrevInstance,
    _In_ LPSTR     lpCmdLine,
    _In_ int       nCmdShow
)

    WNDCLASSEX wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc = WndProc;
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = hInstance;
    wcex.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName = szWindowClass;
    wcex.hIconSm = LoadIcon(wcex.hInstance, IDI_APPLICATION);

    if (!RegisterClassEx(&wcex))
    
        MessageBox(NULL,
            _T("Call to RegisterClassEx failed!"),
            _T("Windows Desktop Guided Tour"),
            NULL);

        return 1;
    

    // Store instance handle in our global variable
    hInst = hInstance;

    // The parameters to CreateWindow explained:
    // szWindowClass: the name of the application
    // szTitle: the text that appears in the title bar
    // WS_OVERLAPPEDWINDOW: the type of window to create
    // CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
    // 500, 100: initial size (width, length)
    // NULL: the parent of this window
    // NULL: this application does not have a menu bar
    // hInstance: the first parameter from WinMain
    // NULL: not used in this application
    HWND hWnd = CreateWindow(
        szWindowClass,
        szTitle,
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT,
        600, 400,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    if (!hWnd)
    
        MessageBox(NULL,
            _T("Call to CreateWindow failed!"),
            _T("Windows Desktop Guided Tour"),
            NULL);

        return 1;
    

    // The parameters to ShowWindow explained:
    // hWnd: the value returned from CreateWindow
    // nCmdShow: the fourth parameter from WinMain
    ShowWindow(hWnd,nCmdShow);
    UpdateWindow(hWnd);

    // Main message loop:
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    
    return (int)msg.wParam;


//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)

    PAINTSTRUCT ps;
    HDC hdc；

    switch (message)
    
    case WM_CREATE:
        hwndButton = CreateWindowW(
            L"BUTTON",  // Predefined class; Unicode assumed 
            L"OK",      // Button text 
            WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON,  // Styles 
            10,         // x position 
            10,         // y position 
            100,        // Button width
            100,        // Button height
            hWnd,     // Parent window
            NULL,       // No menu.
            (HINSTANCE)GetWindowLong(hWnd, GWL_HINSTANCE),
            NULL);      // Pointer not needed.
         break;
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);

        // Here your application is laid out.
        // For this introduction, we just print out "Hello, Windows desktop!"
        // in the top left corner.
        TextOut(hdc, 5, 5, greeting, _tcslen(greeting));
        // End application-specific layout section.
        EndPaint(hWnd, &ps);
        break;

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

【讨论】：

(1) 如果不解释您已更改的内容，这几乎是无用的；(2) 将 WM_PAINT 更改为 WM_CREATE 同时 仍在调用 BeginPaint() 和 EndPaint() 完全错误 @Ben (1) 我在代码注释中说过。 (2) 感谢您的提醒

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