windows 的最简单的窗口程序的处理流程

For example, suppose the user presses the left mouse button. This causes a chain of events:

The operating system places a
WM_LBUTTONDOWN message on the message queue.

Your program calls the
GetMessage function.

GetMessage pulls the

WM_LBUTTONDOWN message from the queue and fills in the

MSG structure.
Your program calls the
TranslateMessage and

DispatchMessage functions.

Inside
DispatchMessage, the operating system calls your window procedure.
Your window procedure can either respond to the message or ignore it.

例如，假设用户按下鼠标左键，这个动作将引发连串反应：

1、操作系统将鼠标左键被按下的事件放入事件队列；
2、你的程序（指自己编写的窗口程序）调用GetMessage函数；
3、GetMessage函数从消息队列中取出鼠标左键被按下这条消息，并将它填入MSG结构的对象中；
4、你的程序调用TranslateMessage 和
DispatchMessage 函数；
5、在DispatchMessage函数中，系统又调用了你程序中的window procedure函数；
6、你的window procedure函数可以回应这条消息，或者忽略这条消息。

配合源码：https://msdn.microsoft.com/zh-cn/library/windows/desktop/ff381409.aspx

#ifndef UNICODE
#define UNICODE
#endif

#include <windows.h>

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
// Register the window class.
const wchar_t CLASS_NAME[]  = L"Sample Window Class";

WNDCLASS wc = { };

wc.lpfnWndProc   = WindowProc;
wc.hInstance     = hInstance;
wc.lpszClassName = CLASS_NAME;

RegisterClass(&wc);

// Create the window.

HWND hwnd = CreateWindowEx(
0,                              // Optional window styles.
CLASS_NAME,                     // Window class
L"Learn to Program Windows",    // Window text
WS_OVERLAPPEDWINDOW,            // Window style

// Size and position
CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

NULL,       // Parent window
NULL,       // Menu
hInstance,  // Instance handle
NULL        // Additional application data
);

if (hwnd == NULL)
{
return 0;
}

ShowWindow(hwnd, nCmdShow);

// Run the message loop.

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

return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_DESTROY:
PostQuitMessage(0);
return 0;

case WM_PAINT:
{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hwnd, &ps);

FillRect(hdc, &ps.rcPaint, (HBRUSH) (COLOR_WINDOW+1));

EndPaint(hwnd, &ps);
}
return 0;

}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}