我正在尝试显示3个窗口，但它无法创建窗口2，我不知道为什么。它创建了第一个窗口，我为其他两个窗口做了同样的事情。
以下是代码：
#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;
}
它不会抛出任何错误，但是在ghSecdWnd == 0上它会显示该错误消息。
答案 0 :(得分：5)
有两个问题：您遇到的问题，以及窗口3问题。
创建第二个窗口后（但在创建第三个窗口之前）调用GetLastError()会产生"Cannot find the window class."。查看课程设置，您已完成以下操作：
wc.hIcon = ::LoadIcon(0, IDI_APPLICATION);
您实际需要的是设置wc2的图标。即使在注册第二个类时检查RegisterClass的返回值，也会导致"The parameter is incorrect."错误，表明wc2存在问题。它也是代码中较早的位置来捕获错误，这总是一件好事。
其次，第三个窗口出现问题。您尚未在其上设置背景画笔。将此行添加到wc3设置：
wc3.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);
您应该始终查看文档，以了解哪些功能失败并采取相应措施。例如，如果CreateWindow失败，则返回值为NULL，您可以调用GetLastError以获取更多信息。您应该基于每个功能执行此操作。这是一个关于Window 2的两个主要功能的示例。请记住，其他人（例如GetStockObject）也可能会失败。
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，您会在返回值下看到它在失败时返回0并声明您可以调用GetLastError()以获取扩展错误信息，因此我输出那。 CreateWindow说的相同，但它是NULL，因为HWND是一个指针。您可以获取所获得的错误代码，并根据MSDN System Error Codes文章进行检查，或者使用FormatMessage与FORMAT_MESSAGE_FROM_SYSTEM一起为您执行此操作。