I have a problem where clicking (anywhere) on a child dialog box within the application's main frame window causes a message box with NULL parent, which was visible, to be hidden behind the main window.
Say for example we have the following Z order (assuming zero is topmost):
MainWindow = 2, Dialog1 = 1, MessageBox = 0
When I click on Dialog1, it brings MainWindow in front of MessageBox , so we end up with:
MessageBox = 2, MainWindow=1, Dialog1 = 0
But these are both error messages (from different threads) and I don't want the user to acknowledge one then potentially ignore the other because it gets buried.
Some key points:
Dialog1 is shown using DoModal() (not overidden) on receipt of a user defined message to MainWindow.
MessageBox is shown from a separate thread. It's parent window is NULL. I can't set it's parent to MainWindow because the error can occur when MainWindow is waiting on a response from the function that triggered the error in the first place, which causes deadlock. This deadlock scenario isn't the case here as it happens, but I can't assume that from the thread that creates the message box.
I tried adding MB_APPLMODAL to the message box style but it didn't help. I don't want to make it topmost - that just irritates people.
Is there actually a way of preventing MainWindow jumping in front of this message box?
Thanks for any help.
You can post message from the thread to Dialog1 so that Dialog1 can show MessageBox instead of the thread showing MessageBox.
If Dialog1 may/may not exist when MessageBox needs to be shown then you may have a mechanism where the message will be processed by MainWindow if Dialog1 doesn't exist.
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 create a new CWindThread in CWinApp::InitInstance(). In that thread, I create a dialog (for displaying a progress bar in that dialog).
After finishing InitInstance(), I close the dialog by calling DestroyWindow() from the dialog, but the application is loosing focus from main window.
I used AfxGetMainWnd()->SetActiveWindow(); to set focus for main window but it is not working.
How can I return the focus to the main window after closing the dialog?
There is no real good way to do that. The focus is set per thread. So there is no "focus" over all windows.
The only chance you have is to set the new foreground window, that belongs to the other thread with SetForegorundWindow. From within the same application this should work without restrictions.
If it doesn't work you need to "synch" both message queues. This is done by AttachThreadInput. If both messages queue are already attached, than there is no problem with settings the focus directly. But the behaviour of the application will change... Please read the docs, of the functions I linked too.
When a modal popup window is displayed, the reason a user cannot interact with the owner window is that it is disabled. When the modal window is destroyed, care must be taken to re-enable the owner window BEFORE destroying the popup as windows cannot activate a disabled window. This is the usual cause of popup windows re-activating the wrong window.
In MFC, suppose I have a dialog box, and in this box, it has a child CListCtrl, then I use mouse to click this CListCtrl, we know that eventually an WM_LBUTTONDOWN message is sent to CListCtrl. My question is: How does this WM_LBUTTONDOWN message get there?
Two possibilities:
Dialog box first gets this WM_LBUTTONDOWN message , and it finds that mouse click occurs in its child window, then it forwards this message to CListCtrl.
CListCtrl first gets this WM_LBUTTONDOWN message, it can process this message, and if it doesn't care it will forward this message to parent window, i.e. dialog box for further processing.
Which one is true?
Thanks.
Input messages are never sent to a window. They are posted to the message queue associated with a window, waiting to be retrieved through one of the message retrieval functions (GetMessage, PeekMessage, etc.).
Depending on whether the dialog box is modal or modeless, messages are retrieved by the nested modal loop (for modal dialogs) or the application's message loop. The message is then passed on to DispatchMessage, to find the recipient (starting from the topmost visible window under the mouse pointer, that is neither disabled nor transparent), and call into the associated window's window procedure. The window procedure can decide, whether it handles the message or not. A window procedure typically calls DefWindowProc to perform default processing, if it doesn't handle a message.
To summarize: The application's message loop (or the nested modal message loop) gets to see the message first, and instructs the window manager to deliver the message to the respective recipient.
A thorough description on Windows message processing is available at About Messages and Message Queues. The description is specific to the Windows API. Since MFC is just a wrapper around the Windows API, the contents apply to MFC as well, even though some of the concepts are hidden in a typical MFC application.
Generally I have some button that opens child window and the second press on this button should close it. I use a touch screen.
The problem is when I try to press the button for closing the child window, it is not pressed the first time, so I need another click.
In order to fix this I am trying to return the focus to the parent window after the child window is opened.
I register the OnShowWindow message and call SetFocus on the parent window:
void CFlashGuidanceSteps::OnShowWindow(BOOL bShow, UINT nStatus)
{
CDialog::OnShowWindow(bShow, nStatus);
GetParent()->SetFocus();
}
While the function is called (I can see it in debugger), the focus is not returned to the parent window.
However, it works with the OnSetFocus event:
void CFlashGuidanceSteps::OnSetFocus(CWnd* pOldWnd)
{
CDialog::OnSetFocus(pOldWnd);
GetParent()->SetFocus();
}
Why is the focus is not retained with the OnShowWindow event?
The explanation
The usual rule in MFC is that OnXxx functions are called in response to similarly named window messages, e.g. WM_Xxx. So OnShowWindow would be called in response to WM_SHOWWINDOW.
And according to the documentation, WM_SHOWWINDOW is
Sent to a window when the window is about to be hidden or shown.
That means it is sent before the window is actually shown. So when you set the focus to the parent window inside of the OnShowWindow function, nothing actually happens because the parent window already has the focus. Then, after OnShowWindow finishes running, the child window is displayed and demands the focus. It is as if you never made any attempt to change the focus.
By contrast, OnSetFocus, which corresponds to WM_SETFOCUS, is not called until after the window has gained the focus. So when you reassign the focus here, it works because the child window doesn't steal the focus back.
The better idea
That explains the behavior you are seeing, and as you know, things work fine when you adjust the focus in OnSetFocus. But this really isn't the best way of solving the problem.
Manually changing the focus when a window gets and/or loses the focus is approaching the problem the wrong way around, and generally error-prone. You'll get all kinds of focus-related bugs that are difficult to debug. You are better off looking for ways to prevent the focus from changing when you don't want it to.
It sounds to me like you want to prevent the child window from getting the focus when it is created. And there is a way to do precisely that.
When you display the child window, presumably by calling the ShowWindow function or its moral equivalent in MFC, you should pass the SW_SHOWNA flag. That causes the window to be shown without activating it (i.e., granting it the focus).
I have a queer sort of problem. Consider the following scenario:
Main window creates a child dialog on click of some button.
Child dialog does some task in a worker thread.
An error occurs during that task causing a message box to be displayed saying something along the lines of "Yikes! Something went wrong.".
Child dialog's 'Cancel' button is clicked on causing the child dialog to be closed.
Message box is still active! Clicking on anything in the message box = crash.
Pseudocode of how things are happening: (please ignore syntactic correctness here)
MainWindowClass mainObj;
void MainWindowClass::OnSomeButtonClick()
{
SomeDialogClass someDialogObj;
someDialogObj.DoModal();
}
int MainWindowClass::doTask()
{
// Do work
if(ERROR)
{
MessageBox("Yikes! Something went wrong.", "Error", MB_OK);
return ERROR;
}
}
///////////////////////////////////////////////////////////////////
// Meanwhile, in another file,
extern MainWindowClass mainObj;
void SomeDialogClass::OnCancel()
{
// Do all cleanup and close dialog
}
int SomeDialogClass::workerThreadFunc()
{
return mainObj.doTask();
}
int SomeDialogClass::DoModal()
{
AfxBeginThread(workerThreadFunc);
// Do all other work and then wait for the worker thread
}
My question is twofold:
On cancel, is there a way to know if any message boxes/dialogs in
the same application are active?
Is my entire design wrong and should I be doing something else altogether?
I thought one of the main reasons to use a modal dialog was its ability to prevent focus from going to parent dialogs. Yet, when that error message box is shown, I can happily click on the dialog and then click on 'Cancel' and pretend that the error message box never showed.
Rather than have your worker thread bring up a modal message box, it should signal the error condition back to the UI thread. My experience of MFC and multi-threading is that having all UI handled in the same thread makes things much simpler and removes these types of error. Having two threads potentially bringing up modal dialogs at the same time is asking for trouble.
I'm kind of new at this, but my suggestions would be if the child is going to be cancelled when there is an error then destroy it before launching the error.
As far as I can tell, the SomeDialogClass is modal, then the parent launches another modal dialog, the MessageBox. Now, if SomeDialogClass was modeless then the message box would appear on top since SomeDialogClass would then be a child of the entire desktop and the sole child of MainWindowClass would be the MessageBox.
I'm under the impression that modal only prevents focus from going to things underneath the modal dialog, not what is launched on top or after it is open. I've done a modal dialog, launched a modeless from it, and could move both around the screen just fine. Additionally, I created a WM_MESSAGE from the modeless dialog back to the modal to announce when it was done so the modeless could finish.