Is there a class/example application for a message-only window that is in C++ Win32?
From the docs for CreateWindow:
hWndParent
[in] Handle to the parent or owner window of the window being created. To
create a child window or an owned
window, supply a valid window handle.
This parameter is optional for pop-up
windows.
Windows 2000/XP: To create a message-only window, supply HWND_MESSAGE or a
handle to an existing message-only window.
Here is some code, from WebKit I think, that sets up a message-only window for timer events.
Here is an article that shows a (possibly overly) fancy way to create an invisible, message-only window: http://www.codeguru.com/cpp/w-p/win32/tutorials/article.php/c12689
If I recall, the standard solution is to create a basic styleless window with a message pump as you normally would, but never call ShowWindow on it. This way you can receive and process the standard messages like WM_QUERYENDSESSION which are sent to all windows.
A message-only window is used when you need to process windows messages in a thread, but you don't actually want to display a window on the screen.
For example, if you want to use a Windows timer, but don't have an existing UI window you could latch on to.
Related
I have created a modeless dialog as a main window, but the window procedure isn't being sent WM_INITDIALOG messages.
Here's what I've done.
Created a dialog template using Visual Studio's resource editor, and
set its class name to a custom class.
Used WNDCLASSEX to register the class, window procedure, as well as
some icons and brush etc.
Used CreateDialog() with the last two parameters set to NULL, (Parent
window, and window procedure).
Created the message loop using IsDialogMessage(), TranslateMessage()
and DispatchMessage();
Returned DefDlgProc() in the window procedure as the default if no
messages were processed.
I can't think of anything else significant. Everything works well except for not receiving WM_INITDIALOG messages.
I've done it this way so the app minimises to the task bar, and I can have a menu if needed.
So my first question is, Have I done anything stupid?
Secondly, should I expect to receive WM_INITDIALOG messages using this system?
And if not, what is a good way to initialise say a combobox with strings.
(I've looked at things like WM_ACTIVATE, WM_ACTIVATEAPP etc, but nothing seems appropriate.
And the combobox isn't created yet at WM_CREATE.)
Thanks in advance.
I realised the answer shortly after posting.
As mentioned in the comments above, it's a window procedure, not a dialog procedure, so I shouldn't have been trying to initialize child windows within the procedure.
So I initialized them outside the procedure, after creating the dialog box and before the message loop.
All the dialog features are working as expected, but it's a main window that can have a menu and minimizes to the taskbar.
I have a Qt based console application, that has to be located on the Windows System Tray (aka Notification Area).
The question: how can I hide the console window instead of minimizing it if the user clicks on "minimize" icon? I know the ShowWindow method, but as I guess, I have to call it asynchronously.
You need to obtain the HWND window handle of the Console window, then you can use ShowWindow to show or hide it in the usual way.
https://msdn.microsoft.com/en-us/library/windows/desktop/ms683175(v=vs.85).aspx
The question is when do you do this? You need to know when the window is minimised in order to know whether to hide it.
You could check this periodically, but you should be careful to ensure you are not preventing laptops etc. from sleeping by doing so.
Alternatively you could install a message hook, or subclass the window, to recieve immediate notifications.
Subclassing the window is probably the best method.
I made a thread to set some text on EditBox on Lobby Dialog. Below is my code.
And MainLobby is the Dialog Class. This project is "Dialog Based MFC Project".
MainLobby Lobby;
_beginthreadex(NULL, 0, ReceiveMessage, (void *)Lobby.GetSafeHwnd(), 0, NULL);
Lobby.DoModal();
But it doesn't work. Where is wrong? I thought hard but I couldn't find the answer.
I tried not Lobby.GetSafeHwnd() but Lobby.m_hwnd
unsigned WINAPI ReceiveMessage(void *arg)
{
HWND hDlg = (HWND)arg;
char msg[BUF_SIZE];
int msgLen;
while( (msgLen = recv(CClientApp::hSocket, msg, BUF_SIZE, 0)) != 0 )
{
SetDlgItemText(hDlg, IDC_LOBBY_CBOX, msg);
}
}
I am using MFC now. I will be glad a good idea.
The device context has to be updated.
Try:
UpdateData(true);
SetDlgItemText(hDlg, IDC_LOBBY_CBOX, msg);
UpdateData(false);
Or try it with a CString member variable for IDC LOBBY CBOX.
It is clear from your code that you are not using MFC properly. A Windows dialog based application does not require the programmer to explicitly create message handlers or receivers, that is what the MFC framework itself is doing for you. There is no reason to call beginthreadex before starting the dialog message loop as part of the DoModal method. When you invoke DoModal on any class descended From Dialog or DialogEX, the window is constructed, the member objects are constructed, and the message loop is started before the WM_INITDIALOG message is sent to the dialog for any other initialization before the dialog window is displayed. Once the window is displayed, the message loop is running, and text will display automatically in an edit control when you send it correctly. Normally one would declare a CEdit object with some name using the Class Wizard in visual studio then map the MFC object to the dialog object. Rather than type out all the details I will refer to this article: http://msdn.microsoft.com/en-us/library/6d1asasd.aspx
The dialog's HWND has not been initialized before DoModal is called. So your thread does not receive the proper HWND. The first place that you can access the correct HWND value is inside the dialog's OnInitDialog member function.
I see two problems in your code.
First you are calling Lobby.GetSafeHwnd before DoModal, so before the window is constructed. You should move the thread creation to the WM_INITDIALOG handler of MainLobby to create the thread there. Or you could create a modeless dialog.
Second you are using _beginthreadex in your MFC code. If you are starting a thread that uses MFC, then you need to start that thread with AfxBeginThread. If you only use CRT, then you use _beginthreadex. If you use neither, then use Windows CreateThread. The reason for this is that each layer (CRT, MFC) needs to do some housekeeping of thread specific information. This can only be done if you call the proper thread creation functions.
Third, you might consider using the MFC socket objects like CAsyncSocket. This object can send windows messages to your dialog if some data is available on the socket. This perfectly fits into your scenario with an MFC dialog that should handle socket data.
Another thing, but you already got that right: to access an MFC GUI object you need to be in the thread of that GUI object. So calling the Windows SetDlgItemText with the raw handle hDlg needs to be done, you cannot call an MFC function here.
BTW, are you sure your overall strategy is right? I don't see how you handle dialog life time, socket life time and how you put both together.
I have a multi-threaded application that may display a MessageBox for a user's interaction. The message box itself is displayed from a worker thread, after a user picks a context menu command from the app's system tray icon, so the user can technically continue using the app while the message box is displayed. This works great until a user issues "Exit" command, at which point I need to find a way to close any open message boxes.
I did my homework and I was able to obtain HWND handle for the main (dialog) window of the message box (using this method.) I checked the HWND to be correct using Spy++, so HWND itself is not the issue. What happens is that when I do PostMessage(hMsgBoxWnd, WM_CLOSE, 0, 0); from another thread to the message box, it simply ignores this message and doesn't close.
Any idea how to close the message-box by its window handle?
MessageBox() simply does not process WM_CLOSE in all sitations:
SendMessage/PostMessage WM_CLOSE to MessageBox window does not always work
You should use PostThreadMessage to post to the threads specific message queue
HWND button = CreateWindowEx(0, "BUTTON", ...);
SetFocus(button); // Button no get focus! :(
Also, I have other controls on my form that I am able to SetFocus() to.
Thanks, Martin
It has been FOREVER since I've had to do this, but...
Were this a dialog, I would tell you to send a WM_NEXTDLGCTL via PostMessage(). The default dialog item message handler would take care of the rest for you setting keyboard focus and selection activation. However, this is a different case if I read this correctly. You're creating both parent and child windows raw on the fly. If this is the case, SetFocus() to the parent window, and handle WM_SETFOCUS on the parent window by bringing it to top, then setting focus on the child window. WM_SETFOCUS, and WM_KILLFOCUS were designed to allow you to switch the 'activated' state of your controls, and most handle it for you (unless your window is an owner draw control or some such). But in a raw window, when your base parent window is sent the focus, you need to appropriately ensure the proper child has it if you're hosting any (think of it as managing your own 'dialog'). Again, normally this is done by the default dialog procedure for you if this were a dialog, but being raw windows you're kind of stuck managing it all yourself.
Though I can't imagine how, I hope that helped somewhat.
SetFocus is a function, not a procedure. Call it as a function and check its returned value. Either the retuned value is null because you made an error in the CreateWindowEx() call and "button" isn't a valid handle or it's a window not associated with your thread's message queue, or the return value is not null (it's now the prior focused window's handle) and you do have the focus (but are somehow failing to detect it).
Try setting the WS_TABSTOP style on the button.
If you create that button in respond of the WM_INITDIALOG message you should return FALSE to prevent dialog box procedure to change the focus.