It’s the WM_NC class messages. For example, you can handle the WM_NCLBUTTONDBLCLK message.

And you can alse reponsible the  WM_SYSCOMMAND messages.  In particular, the special cases of SC_MINIMIZE and SC_MAXIMIZE are what are called from the system menu, which is what is available from the taskbar.

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There are 3 solutions:

Solution 1: Send the message to the main window.

Send/Post the message to the main frame or the view, and then call some functions of the document.

But if in a MDI app, it does not work, because the routing becomes too complex. Typically, you can send message to a view, but that has risks if there are multiple views on the same document and the one you post message to has been closed.

Solution 2: Use WM_COMMAND message.

A document can’t recerive a message, but it can recerives the commands through MFC’s command mechanism. Then you can use ::PostMessage to post WM_COMMAND message, and repose it in the document.

Solution 3:

Create an invisible top-level window in the CDocument, that represents its message sink. You send/post message to it. Thus will eliminate the complex route policy between the main frame and the views and you don’t worry about the view closing.

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I’m trying to create a UI thread to do constant background work, but I’m having some design problems.

The thread needs to fetch records from a database. do some processing on each record and, when there are no more records, sleep for 1 minute before check the database again. The process will be controlled with thread messages (to start, pause, query…).

My problem is where should I put the processing work. I need it to be responsive between cycles, where the process waits for 1 minute, so I can stop it in that period. My only idea is using OnIdle to do the work.
But then, how should I make it real idle when waiting for 1 minute?

Could anyone give some hints on what is the way to go?

Scott McPhillips [VC++ MVP]

You can’t use Sleep and still be responsive to messages. Instead of using Sleep you could use SetTimer in the main thread and post a message to the thread, or SetTimer to a hidden window within the thread, or you could use a loop within the thread and use MsgWaitForMultipleObjects within the loop.

MsgWaitForMultipleObjects has a timeout parameter that gives you the sleep period, but it also returns early if a message or event comes along.

Almond and Joseph M. Newcomer [MVP]

I would be strongly disinclined to use MsgWaitForMultipleObjects. You don’t gain anything by using it over using WM_TIMER, and it requires that you have to write your own message pump, always a dangerous proposition.

BUT, SOME MORE DISCUSSION ABOUT THE UI THREAD AND WORKER THREAD…

Almond

Do not use UI threads for this kind of thing.

David

I would create a worker thread (not a UI thread) unless you need a UI thread for some specific purpose not apparent in this description. The worker thread would do it’s work and then do a WaitForSingleObject() with a timeout of 1 minute (60000 ms), which causes WaitForSingleObject() to return when either the main thread sets an event for starting, pausing, querying, etc. or the 1 minute has elapsed. If you need separate events each for starting, pausing, querying, etc. use WaitForMultipleObjects() instead of WaitForSingleObject().

Joseph M. Newcomer [MVP]

UI threads are actually ideal for this sort of thing. Don’t be confused by the phrase ‘UI’ meaning something with windows; think of it as “a thread with a built-in queuing mechanism”. They’re really very good for things that require timed events as the OP described.

There are some advantages to UI threads; for example, a UI thread has a built-in queue.
Also, for some kinds of interfacing require a message pump to deal with event handling. I don’t do databases so I don’t know if databases have this requirement, but there are On-Anything handlers involved in the database interface, then a UI thread is required.

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I’m trying to create a UI thread to do constant background work, but I’m having some design problems.

The thread needs to fetch records from a database. do some processing on each record and, when there are no more records, sleep for 1 minute before check the database again. The process will be controlled with thread messages (to start, pause, query…).

My problem is where should I put the processing work. I need it to be
responsive between cycles, where the process waits for 1 minute, so I
can stop it in that period. My only idea is using OnIdle to do the work.
  But then, how should I make it real idle when waiting for 1 minute?

Could anyone give some hints on what is the way to go?

Scott McPhillips [VC++ MVP]

You can’t use Sleep and still be responsive to messages.  Instead of using Sleep you could use SetTimer in the main thread and post a message to the thread, or SetTimer to a hidden window within the thread, or you could use a loop within the thread and use MsgWaitForMultipleObjects within the loop.

MsgWaitForMultipleObjects has a timeout parameter that gives you the sleep period, but it also returns early if a message or event comes along.

Almond and Joseph M. Newcomer [MVP]

I would be strongly disinclined to use MsgWaitForMultipleObjects.  You don’t gain anything by using it over using WM_TIMER, and it requires that you have to write your own message pump, always a dangerous proposition.

BUT, SOME MORE DISCUSSION ABOUT THE UI THREAD AND WORKER THREAD…

Almond

Do not use UI threads for this kind of thing.

David

I would create a worker thread (not a UI thread) unless you need a UI thread for some specific purpose not apparent in this description.  The worker thread would do it’s work and then do a WaitForSingleObject() with a timeout of 1 minute (60000 ms), which causes WaitForSingleObject() to return when either the main thread sets an event for starting, pausing, querying, etc. or the 1 minute has elapsed.  If you need separate events each for starting, pausing, querying, etc. use WaitForMultipleObjects() instead of WaitForSingleObject().

Joseph M. Newcomer [MVP]

UI threads are actually ideal for this sort of thing.  Don’t be confused by the phrase ‘UI’ meaning something with windows; think of it as “a thread with a built-in queuing mechanism”.  They’re really very good for things that require timed events as the OP described.

There are some advantages to UI threads; for example, a UI thread has a built-in queue.
Also, for some kinds of interfacing require a message pump to deal with event handling.  I don’t do databases so I don’t know if databases have this requirement, but there are On-Anything handlers involved in the database interface, then a UI thread is required.

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Chinese version author: peach@newsmth.net

Userally, when you install a global hook, you need a dll. But now, you can install WH_KEYBOARD_LL or WH_MOUSE_LL global hook without dll’s help.

The following code was tested under win2k3. And I it will also run on 2k/xp.

#define _WIN32_WINNT 0400
#define STRICT
#define WIN32_LEAN_AND_MEAN

#include
#include
#include

DWORD g_main_tid = 0;
HHOOK g_kb_hook = 0;

BOOL CALLBACK con_handler (DWORD)
{
PostThreadMessage (g_main_tid, WM_QUIT, 0, 0);
return TRUE;
};

LRESULT CALLBACK kb_proc (int code, WPARAM w, LPARAM l)

{
PKBDLLHOOKSTRUCT p = (PKBDLLHOOKSTRUCT)l;
const char *info = NULL;
if (w == WM_KEYDOWN)
info = “key dn”;
else if (w == WM_KEYUP)
info = “key up”;
else if (w == WM_SYSKEYDOWN)
info = “sys key dn”;
else if (w == WM_SYSKEYUP)
info = “sys key up”;

printf (“%s – vkCode [%04x], scanCode [%04x]\n”,
info, p->vkCode, p->scanCode);
// always call next hook
return CallNextHookEx (g_kb_hook, code, w, l);

};

int main (void)
{
g_main_tid = GetCurrentThreadId ();
SetConsoleCtrlHandler (&con_handler, TRUE);

g_kb_hook = SetWindowsHookEx (
WH_KEYBOARD_LL,
&kb_proc,
GetModuleHandle (NULL), //　It shouldn’t be NULL, or will fail
0);

if (g_kb_hook == NULL)

{
fprintf (stderr,
“SetWindowsHookEx failed with error %d\n”,
::GetLastError ());
return 0;
};

// The message loop is necesarry

MSG msg;
while (GetMessage (&msg, NULL, 0, 0))
{
TranslateMessage (&msg);
DispatchMessage (&msg);
};
UnhookWindowsHookEx (g_kb_hook);
return 0;
};

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Such problem often occures because of incorrect signature of message handle functions, that included into MFC message map for your CWnd based class.
We should very carefully check signatures such functions in comparision with expected one by MFC library. For example, if you put follow handler into message map

ON_MESSAGE(WM_SOME_USER_MESSAGE, OnMyMessage)

and define OnMyMessage as:

void CMyWnd::OnMyMessage()
{
//do something
}

this code will be compiled without errors. DEBUG build can work without any problems, but RELEASE will crash besause ON_MESSAGE macro expect follow
signature:

LRESULT CMyWnd::OnMyMessage(WPARAM /*wParam*/, LPARAM /*lParam*/)

DEBUG build works because stack processing has differences for debug and release builds.

so, the solution is simple:

Solution 1:  modify the  message handle functions with the following style and it will be ok.

void CMyWnd::OnMyMessage(WPARAM wParam, LPARAM lParam)

Solution 2:  don’t modify the message handle functios, and change the ON_MESSAGE macro to ON_MESSAGE_VOID.

ON_MESSAGE_VOID(WM_SOME_USER_MESSAGE, OnMyMessage)


This macro is in AfxPriv.h, but is largely undocumented.

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Alex Rest found the WM_NULL message and was curious where somebody would need to use that.