I am using C++ with MFC, and I have a ListBox tied to a variable that I'm updating as I run through a function:
void CFileSelection::OnBnClickedFiletousb()
{
m_LogC.AddString(_T("Starting move to USB, Please Wait..."));
UpdateData(FALSE);
// Code to move files from disk to USB
m_LogC.AddString(_T("Move to USB Successful."));
}
However, despite the UpdateData, the ListBox doesn't populate with either string until it has completed it's task. Is there a way to make it update the screen before the rest of the code is executed?
Use this function after changing the text on the listbox. Your issue is that the other calls are blocking the MessageThread, but you can force an update with this.
void ProcessWindowMessages()
{
MSG msg;
while (::PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) // let them see the message before we go into longer term wait
{
TranslateMessage(&msg); // translate it
DispatchMessage(&msg); // and let windows dispatch it to WinProc
}
}
Alternatively you can also call
yourlistboxVariable->UpdateWindow();
Related
On GetMessage reference from microsoft we have the next example:
BOOL bRet;
while( (bRet = GetMessage( &msg, hWnd, 0, 0 )) != 0)
{
if (bRet == -1)
{
// handle the error and possibly exit
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
What if I just ignore unhandled messages in the main loop of my program and move on?
Is there any risk to it? Will Windows complain/leak memory/hold resources for longer than necessary if I don't translate+dispatch this message if I don't actually need/want to handle it?
According The Message Loop,
The TranslateMessage function is related to keyboard input. It
translates keystrokes (key down, key up) into characters. You do not
really have to know how this function works; just remember to call it
before DispatchMessage. The link to the MSDN documentation will give
you more information, if you are curious.
The DispatchMessage function tells the operating system to call the
window procedure of the window that is the target of the message. In
other words, the operating system looks up the window handle in its
table of windows, finds the function pointer associated with the
window, and invokes the function.
If I don't translate+dispatch, loop will not be able to handle keyboard input and window messages. For example, the window cannot be moved, cannot be redrawn or closed. This has nothing to do with memory leaks
Having said that, a standard Message loop should be:
while (GetMessage(&msg, NULL, 0, 0))
{
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
Accelerators are what matters here, otherwise known as "short-cut keys". Your program wants to respond to them regardless of which window has the focus. Like F1 shows the program's help file, regardless which control has the focus. You don't want to have to write code that subclasses every control window to recognize F1.
Refer: why exactly TranslateMessage
Following a Direct2D tuturial I've created a realtime update&render-loop like below. But when the update&render-loop takes long (eg when I have a Sleep(5000) somewhere in the Update()), normal messages handling like clicking the close window, can have to wait up to 5s.
So what is the proper way to split the message handling and realtime update&render-loop in two separate threads?
while (message.message != WM_QUIT)
{
if (PeekMessage(&message, windowHandle, 0, 0, PM_REMOVE)) // check for events and pass them to WindowProc, otherwise
DispatchMessage(&message);
else // run the realtime update&render loop
{
GameController::Update();
graphics->BeginDraw();
GameController::Render();
graphics->EndDraw();
}
}
I am attempting to disable a window under certain conditions using EnableWindow(hWnd, false);
According to the documentation, this should "disable mouse and keyboard input to the specified window".
The problem I am seeing is that it does, in fact, disable like it says, except if the cursor is currently inside of a text box in the window and the window has the focus that does not get disabled. I was thinking of doing some sort of code to take the focus off of the window as well.
Is there a better way to go about this?
Note: The window being disabled is a binary ran via _spawnl().
I'm not sure if this is a Windows feature or a bug. Either way, disabling the foreground window is not a good idea.
If you are able to modify the program you start with _spawnl() then that is a better solution. You could make it respond to WM_APP or something like that when you need to control it.
If it is a 3rd-party application then you are left with hacks.
You could try to change the foreground window with SetForegroundWindow but this will only work if you do it very soon after _spawnl() before your thread loses the foreground lock. Using LockSetForegroundWindow before _spawnl() might be able to help you keep the lock longer. There are also various other hacks to change the foreground with AttachThreadInput etc.
If you don't want to change the foreground I was able to come up with a workaround:
ShellExecute(NULL, NULL, TEXT("Notepad"), NULL, NULL, SW_SHOW);
Sleep(2000);
HWND hNP = FindWindow(TEXT("Notepad"), NULL);
Sleep(2000); // Start typing in Notepad now...
if (hNP)
{
DWORD tid = GetWindowThreadProcessId(hNP, NULL);
GUITHREADINFO gti;
gti.cbSize = sizeof(gti);
if (tid && GetGUIThreadInfo(tid, >i))
{
HWND hChild = NULL;
if (gti.hwndFocus != hNP && gti.hwndFocus)
{
EnableWindow(hChild = gti.hwndFocus, false);
}
if (GetForegroundWindow() == hNP)
{
SendNotifyMessage(hNP, WM_ACTIVATE, WA_INACTIVE, NULL);
SendNotifyMessage(hNP, WM_ACTIVATE, WA_ACTIVE, NULL);
SendNotifyMessage(hNP, WM_SETFOCUS, NULL, NULL);
// SendNotifyMessage(hNP, WM_NCACTIVATE, false, NULL); // Uncomment to make it look like it is inactive
}
EnableWindow(hNP, false);
if (hChild)
{
EnableWindow(hChild, true);
}
}
MessageBox(NULL, TEXT("Done?"), NULL, MB_TOPMOST);
SetForegroundWindow(hNP);
PostMessage(hNP, WM_CLOSE, 0, 0);
}
This is certainly not optimal, it leaves Notepad in a state where it looks like it is enabled but it is really not. The idea is to disable the focused child window and trigger a fake activation change and forcing the focus to change. It might not work with other applications, who knows.
If you are willing to risk a deadlock you can do this instead:
DWORD tid = GetWindowThreadProcessId(hNP, NULL);
GUITHREADINFO gti;
gti.cbSize = sizeof(gti);
if (tid && GetGUIThreadInfo(tid, >i))
{
if (GetForegroundWindow() == hNP)
{
if (AttachThreadInput(GetCurrentThreadId(), tid, true))
{
SetFocus(NULL);
AttachThreadInput(GetCurrentThreadId(), tid, false);
}
}
EnableWindow(hNP, false);
}
I am just learning to create a gui using the winapi, but i have run into an issue. I can create a window like this
#include "stdafx.h"
#include <windows.h>
int main()
{
HWND hwnd = CreateWindow(L"STATIC",NULL,WS_VISIBLE|WS_SYSMENU|WS_CAPTION,0,0,600,600,NULL,NULL,NULL,NULL);
UpdateWindow(hwnd);
MSG msg;
while(GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
_gettch();
}
But the windows will not close when the close button is clicked, and the window can not be dragged around or moved. I was wondering how i would enable these features of the window.
Static windows are not there for normal windows, you should try and look up how to register and handle your own class with RegisterWindowEx then use the same class name to create a window. You have to have your own window procedure in order to handle messages.
All window classes registered by the system run their own default window procudure and as far as I know none of them handle WM_CLOSE ( that is the close button ) this is why you can't close it.
For you main windows always use something like WS_OVERLAPPEDWINDOW so it'll be clear if it's okay or not and from that eliminate the flags you don't need.
How you set it up :
WNDCLASSEX wndcls;
HWND hMainWnd;
// Register your own window class
ZeroMemory(&wndcls,sizeof(WNDCLASSEX));
wndcls.cbSize=sizeof(WNDCLASSEX);
wndcls.style=CS_VREDRAW+CS_HREDRAW;
wndcls.lpfnWndProc=&appWndFunc;
wndcls.hInstance=hInstance;
wndcls.hIcon=hMainIcon; // or just LoadIcon(hInstance,MAKEINTRESOURCE(IDI_MAIN_ICON))
wndcls.hIconSm=hMainIcon;
wndcls.hCursor=LoadCursor((HINSTANCE)NULL,IDC_ARROW);
wndcls.hbrBackground=(HBRUSH)COLOR_APPWORKSPACE;
wndcls.lpszClassName="myWndClass";
if (RegisterClassEx(&wndcls)==0)
{
// failed to register class name
return false;
}
// Create window with your own class
hMainWnd=CreateWindowEx(0,\
"myWndClass","widnow title",\
WS_OVERLAPPEDWINDOW|WS_VISIBLE,\
0,\
0,\
250,\
250,\
hMainWnd,NULL,hInstance,NULL);
if (hMainWnd==(HWND)NULL)
{
// failed to create main window
return false;
}
Then your main loop :
bool bAppMainLoop=false
while(!bAppMainLoop)
{
WaitMessage();
while(PeekMessage(&emsg,NULL,0,0,PM_NOREMOVE))
{
if(GetMessage(&emsg,NULL,0,0)==0)
{
bAppMainLoop=true;
break;
}
TranslateMessage(&emsg);
DispatchMessage(&emsg);
}
}
This is a bit more than usual setup, so let me explain , in order to not burn CPU, you wait for a message with WaitMessage, it'll block until something happens, like move window, click, paint etc. PeekMessage will return true if there is a message so calling it in a while loop will make sure it drains the message quene, GetMessage will obtain the message if it returns 0 it means that your app called the PostQuitMessage(0) so a WM_QUIT arrived was found in the message loop that means it's time to break out from the message loop. The rest Translate and Dispatch does what it name says.
Finally you need your own window procedure :
LRESULT CALLBACK appWndFunc(HWND hWnd,UINT uMsg,WPARAM wParam,LPARAM lParam)
{
if (uMsg==WM_CLOSE)
{
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hWnd,uMsg,wParam,lParam);
}
DefWindowProc is essential that handles all commonly occurring messages from the system, thus you don't need to handle those here. You simply respond to the WM_CLOSE message which is sent when you want to close the window and post a quit message into the message loop that you will catch and exit.
Additional info :
It's not required to release your stuff since windows does that for you so it wont be locked the next time you start your program , but it's a good practice to at least Unregister your window class after your main loop.
Btw that is the wrong main function : WinMain that is the correct one. Plus to avoid even more bugs make sure you compile a windows GUI application.
I'm new to native c++. Right now, I made it so when I press the left mouse button, it has a for loop that does InvalidateRect and draws a rectangle, and increments X by the box size each time it iterates. But, C++ is so much faster and efficient at drawing than C# that, it draws all this instantly. What I would like is for it to invalidate the rectangle, show the rectangle, wait 50ms, then continue the loop. I tried Sleep(50) but it still waits until painting is done before showing the result. I also tried PeekMessage but it did not change anything.
Any help would be appreciated. Thanks
DoEvents basically translates as:
void DoEvents()
{
MSG msg;
BOOL result;
while ( ::PeekMessage(&msg, NULL, 0, 0, PM_NOREMOVE ) )
{
result = ::GetMessage(&msg, NULL, 0, 0);
if (result == 0) // WM_QUIT
{
::PostQuitMessage(msg.wParam);
break;
}
else if (result == -1)
{
// Handle errors/exit application, etc.
}
else
{
::TranslateMessage(&msg);
:: DispatchMessage(&msg);
}
}
}
I am a bit rusty in Win32 API, but the asynchronous way of doing this would be:
Invalidate the rect
Set a timer (see below) to send a message after 50ms
Return to the event loop to let WM_PAINT events happen
On receiving the timer message, move the rect, then repeat
This way integrates nicely with being event driven. I realize this is not exactly what you ask for, but I thought I'd mention it as a possible solution anyway :)
EDIT: A quick google turns up the Windows API call [SetTimer](http://msdn.microsoft.com/en-us/library/ms644906(VS.85,loband).aspx) which you can use to facilitate this. The message will be a WM_TIMER one.