I am creating a barcode generator application in win32. I got the library to generate the needed barcodes and if I hardcode the UPC it displays the barcode fine. However I want to be able to enter a string in the text field and have it generate the barcode and display it on the window.
I've looked into UpdateWindow, but the HWND variable that is in
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
is out of scope in the function that I want to call it in, and I've also tried making a global HWND hWnd, but it throws a compiler error.
If this is not enough information, please let me know so I can update it with the necessary information.
I should have read the error more carefully.
The error was the redefinition of a variable. Just deleted the later definition and the problem went away.
Sorry!
Related
Message WM_INITMENU is supposed to contain menu handle in wParam. For some reason, for system menu, wParam is something different. Sometimes it is even negative number. However, it is always the same within the same instance.
I can ignore wParam and use the handle, returned by GetSystemMenu, to modify menu items - all works. I don't have other menus and can skip the check, but it is doesn't look accurate.
This is simple desktop C++ non-MFC project on Windows 10 21h1. I have a few other messages and all of them have expected wParam, so it must be "by design". Microsoft docs did not tell anything special. Maybe somebody knows, what is the value in wParam?
Thanks--
I'm trying to disable windows keys for a window that uses RawInput to process keyboard events. The usual way to do this is to install a low-level keyboard hook and filter out windows key events there. In order for it to work with RawInput, I have to initialize the keyboard device with RIDEV_NOHOTKEYS. However, when I do that, if I then Alt+Tab from the app, for some reason Windows 10 displays the classic Alt+Tab thing:
I'm not filtering out Alt or Tab events in the low-level keyboard hook, and this also happens if I don't install a low-level keyboard hook at all, just initializing the keyboard device with RIDEV_NOHOTKEYS does it. I tried returning 0 for WM_INPUT messages, and I tried calling the default window proc, nothing seems to be helping... Has anyone had this issue before?
Add a low level hook (WH_KEYBOARD_LL) can prevent Alt key message to pass to other windows. Refer to "LowLevelKeyboardProc callback function".
WH_KEYBOARD_LL hook can be set only with global scope.
// Register hook
hinstDLL = LoadLibrary(TEXT("sysmsg.dll"));
hkprcSysMsg = (SYSMESSAGEPROC)GetProcAddress(hinstDLL, "SysMessageProc");
HHOOK hook = SetWindowsHookEx(WH_KEYBOARD_LL, (HOOKPROC)hkprcSysMsg, hinstDLL, 0);
Hook callback function in DLL:
__declspec(dllexport)
LRESULT __cdecl SysMessageProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if (nCode < 0) // do not process message
return CallNextHookEx(NULL, nCode,
wParam, lParam);
if (wParam == WM_SYSKEYDOWN)
{
if(((tagKBDLLHOOKSTRUCT*)lParam)->vkCode == VK_LMENU || ((tagKBDLLHOOKSTRUCT*)lParam)->vkCode == VK_RMENU)
return 1;
}
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
More reference: "Using Hooks" "Keyboard Input" "WM_SYSKEYDOWN message" "KBDLLHOOKSTRUCT structure" "Virtual-Key Codes"
Note
Hooks tend to slow down the system because they increase the amount of
processing the system must perform for each message. You should
install a hook only when necessary, and remove it as soon as possible.
You should use global hooks only for debugging purposes; otherwise,
you should avoid them. Global hooks hurt system performance and cause
conflicts with other applications that implement the same type of
global hook.
I am writing a program that automates saving data to a specific location, based on the common Save/Save As dialog.
There are two attacking approaches. Both approaches require monitoring handles for messages under Spyxx (so essentially we are trying to replicate the SendMessage)
The first approach to set the File Name with target path, using Win32 SendMessage API. The HWnd in this case is the Edit field next to the File name.
[DllImport("user32.dll")]
public static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, [MarshalAs(UnmanagedType.LPStr)] string lParam);
SendMessage(HWnd, (int)WindowMessage.WM_SETTEXT, IntPtr.Zero, #"Address: %UserProfile%\Desktop\Target.txt");
The problem with this approach is that, it does not always set the text under Windows 7 and Windows 8.1 (I do have better luck with Windows 10). I tried to set some waiting time, but no matter how long I wait, it doesn't seem to matter (besides SendMessage is synchronous operation, so text should be set, or not set at all)
The second approach is to set the Location at the top of the dialog box. Again, we are using SendMessage to accomplish this, and HWnd in this case, references the ToolbarWindow32 object, which is the child of Breadcrumb Parent object.
SendMessage(HWnd, (int)WindowMessage.WM_SETTEXT, IntPtr.Zero, #"Address: %UserProfile%\Desktop");
or
SendMessage(HWnd, (int)WindowMessage.WM_SETTEXT, IntPtr.Zero, #"Address: Desktop"); // replicated message found on Spyxx
Unfortunately, this approach does not seem to work (i.e. I can send the message, but Dialog doesn't change its location), and I have yet to figure out what steps I am missing.
My question, how do you use Win32 API to interact with the 3rd party app's Save As dialog, so that you can guarantee saving the file in the desired location? Much appreciated and thanks for reading!
I'm a bit confused by the MSDN page for WM_PRINTCLIENT and related functionality in a few ways:
What value should I return from my window procedure? The documentation is missing a "Return value" section entirely. (It is also missing in the Visual Studio 2012 offline documentation disc's version of the page.) Raymond Chen's original scratch program returns zero; is this the preferred option?
The summary and Remarks section for WM_PRINTCLIENT indicates that I should only draw the client area, but the LPARAM lists all the possible WM_PRINT flags — so what should I do, ignore it and unconditionally draw just the client area or draw everything requested? (My intention with this question is not to second-guess the documentation; I'm just looking to implement this message correctly.)
I want to, as a convenience/kindness, provide the WM_PAINT with DC in wParam functionality mentioned in the WM_PAINT documentation as an option as well. How should I interpret LPARAM in this case? Or is there a reason I shouldn't provide this alternative route? (Corollary: if LPARAM is to be ignored, should I draw the entire client area unconditionally?)
Thanks.
Update Rephrasing the third part:
The documentation for WM_PAINT includes the paragraph
For some common controls, the default WM_PAINT message processing checks the wParam parameter. If wParam is non-NULL, the control assumes that the value is an HDC and paints using that device context.
I would like to provide this behavior in my control in addition to WM_PRINTCLIENT for completeness's sake. Is there a reason I should NOT do so? And if doing so wouldn't hurt, how should I interpret the lParam, and should I draw the entire client rect?
What value should I return from my window procedure?
You return 0 to indicate that the message was handled. Do not call DefWindowProc().
but the LPARAM lists all the possible WM_PRINT flags
That was a bit sloppy, a copy/paste fumble from the WM_PRINT article. The only flags you should test are PRF_ERASEBKGND, but only if you draw method requires having the background painted, and PRF_CLIENT, which will always be set in common usage of the message.
How should I interpret LPARAM in this case?
Hard to decode that question, WM_PAINT doesn't use the lparam argument. But yes, you want a common function that implements the painting so you can call it both from your WM_PAINT and your WM_PRINTCLIENT message handlers. Boilerplate code in your window procedure ought to look like:
case WM_PAINT: {
HDC hdc = BeginPaint(hWnd, &ps);
Draw(hdc);
EndPaint(hWnd, &ps);
break;
}
case WM_PRINTCLIENT: {
HDC hdc = (HDC)wParam;
DWORD flags = (DWORD)lParam;
if (flags & PRF_ERASEBKGND) SendMessage(hWnd, WM_ERASEBKGND, (WPARAM)hdc, NULL);
if (flags & PRF_CLIENT) Draw(hdc);
break;
}
Where void Draw(HDC hdc) is your common paint function.
This question already has answers here:
What is HWND in VC++
(5 answers)
Closed 3 years ago.
I was testing some Win32 apps with c++, and in this code:
LRESULT CALLBACK WindowProc(
_In_ HWND hwnd,
_In_ UINT uMsg,
_In_ WPARAM wParam,
_In_ LPARAM lParam
);
Looking at this MSDN Documentation, I couldn't really understand what the HWND is?
It says: A handle to the window.. What does that mean?
The answer is there behind the "Conceptual" section link on the MSDN page you refer to.
About Windows - Window Handle:
Window Handle
After creating a window, the creation function returns a window handle
that uniquely identifies the window. A window handle has the HWND data
type; an application must use this type when declaring a variable that
holds a window handle. An application uses this handle in other
functions to direct their actions to the window.
About Window Procedures
Structure of a Window Procedure
A window procedure is a function that has four parameters and returns
a signed value. The parameters consist of a window handle, a UINT
message identifier, and two message parameters declared with the
WPARAM and LPARAM data types. For more information, see WindowProc.