你好有人可以回答我为什么当我运行这个程序时 MessageBoxes 的顺序是 1,2,4,3 而不是 1,2,3,4。在我看来,程序应该在启动 WM_USER+11 之前结束执行 WM_PAINT 过程,为什么不呢?
// Win32Project6.cpp : Defines the entry point for the application.
//
#include "stdafx.h"
#include "Win32Project6.h"
#define MAX_LOADSTRING 100
// Global Variables:
HINSTANCE hInst; // current instance
TCHAR szTitle[MAX_LOADSTRING]; // The title bar text
TCHAR szWindowClass[MAX_LOADSTRING]; // the main window class name
// Forward declarations of functions included in this code module:
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK About(HWND, UINT, WPARAM, LPARAM);
DWORD thread(LPVOID lpdwThreadParam);
int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPTSTR lpCmdLine,
_In_ int nCmdShow)
{
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);
// TODO: Place code here.
MSG msg;
HACCEL hAccelTable;
// Initialize global strings
LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
LoadString(hInstance, IDC_WIN32PROJECT6, szWindowClass, MAX_LOADSTRING);
MyRegisterClass(hInstance);
// Perform application initialization:
if (!InitInstance (hInstance, nCmdShow))
{
return FALSE;
}
hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_WIN32PROJECT6));
// Main message loop:
while (GetMessage(&msg, NULL, 0, 0))
{
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return (int) msg.wParam;
}
//
// FUNCTION: MyRegisterClass()
//
// PURPOSE: Registers the window class.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
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, MAKEINTRESOURCE(IDI_WIN32PROJECT6));
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName = MAKEINTRESOURCE(IDC_WIN32PROJECT6);
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));
return RegisterClassEx(&wcex);
}
//
// FUNCTION: InitInstance(HINSTANCE, int)
//
// PURPOSE: Saves instance handle and creates main window
//
// COMMENTS:
//
// In this function, we save the instance handle in a global variable and
// create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
HWND hWnd;
hInst = hInstance; // Store instance handle in our global variable
hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);
if (!hWnd)
{
return FALSE;
}
// PostMessage(hWnd, WM_USER + 11, 0, 0);
MessageBox(0,"1","Message",0);
MessageBox(0, "2", "Message", 0);
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
return TRUE;
}
//
// FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// PURPOSE: Processes messages for the main window.
//
// WM_COMMAND - process the application menu
// 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)
{
int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;
switch (message)
{
case WM_COMMAND:
wmId = LOWORD(wParam);
wmEvent = HIWORD(wParam);
// Parse the menu selections:
switch (wmId)
{
case IDM_ABOUT:
DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
break;
case IDM_EXIT:
DestroyWindow(hWnd);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
break;
case WM_USER+11:
MessageBox(hWnd,"4","Message",0);
break;
case WM_PAINT:
hdc = BeginPaint(hWnd, &ps);
CreateThread(0, 0, (LPTHREAD_START_ROUTINE)&thread, &hWnd, 0, 0);
MessageBox(hWnd, "3", "Message", 0);
// TODO: Add any drawing code here...
EndPaint(hWnd, &ps);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
UNREFERENCED_PARAMETER(lParam);
switch (message)
{
case WM_INITDIALOG:
return (INT_PTR)TRUE;
case WM_COMMAND:
if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
{
EndDialog(hDlg, LOWORD(wParam));
return (INT_PTR)TRUE;
}
break;
}
return (INT_PTR)FALSE;
}
DWORD thread(LPVOID lpdwThreadParam)
{
PostMessage(*(HWND*)(lpdwThreadParam), WM_USER + 11, 0, 0);
return 0;
}
最佳答案
关于这段代码的一些说明:
- 您不应在
WM_PAINT
中创建线程。您也不应该在WM_PAINT
中调用MessageBox
。WM_PAINT
仅用于绘制窗口;这里不应执行其他逻辑。系统优化了WM_PAINT
调用,当您在此处理程序中开始逾期欢迎时,行为会变得非常棘手。 - 您也不应该像使用
(LPTHREAD_START_ROUTINE)&thread
那样转换函数调用。如果您的函数类型不正确,请更改函数原型(prototype);不要只是试图隐藏编译器的警告。 - 您可能应该使用
_beginthread
,因为 CRT 需要执行一些初始化。 - 您应该将
hWnd
作为线程参数传递,而不是&hWnd
。指针可能超出范围并变得无效。这是一个严重的错误。
要真正了解发生了什么,您应该先修复这些错误。
回答你的问题,不同的线程没有速度保证。拆分线程后,现在不知道接下来会发生什么。它们是异步的。也许线程代码比您的主线程运行得更快,反之亦然。
请记住,MessageBox
有其自己的内部消息循环。因此 WM_USER+11
(MessageBox4) 处的调用堆栈将如下所示:
MessageBox (4)
WndProc (WM_USER+11)
DispatchMessage
MessageBox (3), before it's actually shown
WndProc (WM_PAINT)
DispatchMessage
WinMain
因此您可以看到,如果线程发布消息的速度足够快,它会在显示 MessageBox(3)
之前得到处理。
我的猜测是,如果您使用更简单的调试技术(例如 OutputDebugString
),您将观察到更可预测的行为。
关于c++ - WinApi 消息循环,Postmessage 与 SendMessage 类似,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/21758056/